L-Glutamine Caps 500 mg [Discontinued] by Country Life

EFFECTIVE

• Sickle cell disease. A specific oral glutamine powder (Endari, Emmaus Medical, Inc) is approved by the US Food and Drug Administration (FDA) to reduce acute complications of sickle cell disease. Details: Clinical research in adults and children 5 years of age and older shows that taking glutamine 5-15 grams (0.3 grams/kg body weight) orally twice daily for 48 weeks, either with or without hydroxyurea, delays the median time to first crisis by 30 days, and reduces the incidence of acute chest syndrome by 15%, number of hospitalizations by 33%, and the number of hospitalized days by 40%, when compared with placebo (96519,99414).

POSSIBLY EFFECTIVE

• Burns. Oral glutamine seems to improve healing in patients with severe burns and may also reduce the risk for burn wound infections; however, it is unclear if glutamine improves hospitalization length or mortality. Details: Some clinical research shows that administering enteral nutrition supplemented with glutamine 0.35-0.5 grams/kg daily for 12-14 days, beginning within 24-48 hours of hospitalization for severe burn injury (excluding inhalation injury), decreases the length of hospital stay by 6-9 days and may shorten wound healing when compared to control enteral nutrition (52307,52337). A clinical study in adults with moderate to severe burns (including inhalation injury) shows that administering enteral nutrition supplemented with intravenous alanyl glutamine 0.5 grams/kg daily, beginning within 24 hours of burn injury and continued for 14 days, may improve burn-induced organ damage, particularly intestinal mucosal injury, but does not improve mortality or length of hospitalization, when compared with standard nutritional support (108027). Another study in the same population shows that administering enteral nutrition supplemented with glutamine 4.3 grams every 4 hours, beginning within 24 hours of burn injury, decreases the risk of mortality by 83% and the risk of Pseudomonas wound infections; however, it does not decrease the duration of hospitalization (52311). A meta-analysis of these trials and one additional trial shows that administering glutamine enterally reduces the risk of Gram-negative bacterial wound infections by 73% and reduces the risk of mortality by 87% when compared to a control group. However, there was no difference in length of stay or overall wound infection rate (97363). Results were based on a small number of patients within each outcome evaluation. Intravenous glutamine has also been evaluated. One small clinical study shows that intravenous glutamine 0.57 grams/kg daily decreases the incidence of Gram-negative bacteremia by 35% when compared with control in patients with severe burns. However, it does not appear to decrease the incidence of Gram-positive bacteremia, the need to use antibiotics, or risk of mortality (52272).
• Critical illness (trauma). Oral and intravenous glutamine seem to reduce infectious complications in critically ill adults. However, glutamine does not seem to reduce mortality in this population. Details: Some studies show that glutamine reduces the risk of infectious complications in critically ill, multiple-trauma, or postoperative adult patients (5449,5450,7309,7731,8184,52288,52359). However, other studies show no benefit (52308,52360,97362). Meta-analyses of these and other clinical trials suggest that glutamine supplementation reduces the risk of nosocomial infections in critically ill patients by 15% to 18% and the risk of nosocomial infections in surgical patients by 30% to 41%. This benefit was seen only with parenteral glutamine; enteral glutamine does not appear to reduce the risk for nosocomial infection (91355,91358). The role of glutamine for reducing mortality in critically ill adults is conflicting. Some clinical trials suggest that glutamine-enriched enteral and parenteral nutrition reduces mortality in critically ill patients (52283,52289,52408). However, other studies show no benefit (52288,52308,52354,52359,97362). Meta-analyses of results from these and other clinical trials show that, overall, taking glutamine does not reduce the risk of mortality in critically ill patients (91355,91358). However, the dose and dosage form may affect outcomes. One meta-analysis shows that glutamine does not affect the risk of mortality when administered at doses up to 0.5 grams/kg daily, although doses greater than 0.5 grams/kg daily may INCREASE mortality by 18% (91355). Another meta-analysis shows that glutamine decreases short-term mortality in critically ill patients by 25% when administered parenterally, but not enterally (91358). Neither parenteral nor enteral glutamine appears to decrease the risk of long-term mortality in critically ill patients (91358). Research evaluating glutamine in critically ill children is limited. One clinical study in children ages 1-17 admitted to an intensive care unit (ICU) shows that enteral administration of glutamine along with zinc, selenium, and intravenous metoclopramide does not reduce nosocomial infections when compared with whey supplementation (86095).
• HIV/AIDS-related wasting. Oral glutamine seems to attenuate weight loss related to HIV/AIDS. Details: Very small clinical studies show that taking glutamine orally seems to enhance intestinal absorption of nutrients, decrease intestinal permeability, and increase weight gain in adults with HIV/AIDS when compared with placebo. Doses of 40 grams daily seem to produce the greatest effect (2337,2702). Lower doses of 14 grams daily might also be effective when used in combination with arginine and hydroxymethylbutyrate (a leucine metabolite) (7310).
• Postoperative recovery. Oral or intravenous glutamine seems to reduce the duration of hospitalization and improve postoperative nutritional status in adults. However, it does not seem to reduce postoperative mortality. Details: Although some conflicting evidence exists (52316), most clinical research shows that receiving free glutamine or glutamine-containing dipeptide intravenously decreases the duration of hospitalization after surgery, particularly after major abdominal surgery (2363,5448,7300,7732,52275,52341). A meta-analysis of this research and other studies shows that IV supplementation with glutamine-containing dipeptides reduces the length of hospital stay by 3 days when compared with no supplementation (96507). Other meta-analyses of clinical research also show that glutamine supplementation, as free glutamine or glutamine-containing dipeptides, reduces the risk of hospital-acquired infections by 30% in surgical intensive care unit (ICU) patients and by 41% in elective surgical patients (91355,91358). In cancer patients undergoing abdominal surgery, glutamine-supplemented parenteral nutrition seems to improve nutritional status and gastrointestinal function (100943). Glutamine-containing dipeptides also appear to help to preserve intestinal integrity (7299,7300,7732,52306). One small study has evaluated oral glutamine 10 grams, in combination with arginine 4.5 grams, in patients undergoing surgery for enterocutaneous fistulas. This study shows that taking this combination daily for 7 days prior to surgery reduces recurrence of fistulas by 35%, and also reduces postoperative infections (103837). Although glutamine seems to decrease length of stay and reduce infection rate, it does not appear to reduce the risk of mortality in either surgical ICU or elective surgical patients (91355,91358,96509,103834), including those receiving major abdominal surgery (5448,52316,91355,96507). Additionally, most research shows that glutamine supplementation does not reduce the incidence of infectious complications following abdominal surgery (52306,52316,52341,5448,7300,96507). The effects of glutamine on reducing infection rate might be related to patient population, modes of nutrition, or dose of glutamine. Taking a combination of glutamine 7 grams, arginine 7 grams, and hydroxymethylbutyrate 1.2 grams (Abound, Abbott) orally daily for 3 days before and 7 days after abdominal surgery does not reduce the incidence of wound infections or other complications (99413). Most of the research evaluating glutamine in surgical patients has been conducted in adults. Information in children is limited. Existing clinical research shows that glutamine-fortified parenteral nutrition does not improve intestinal permeability, nitrogen balance, duration of hospitalization, incidence of infectious complications, or risk of mortality in newborns and infants undergoing digestive-tract surgery (52338,96508).

POSSIBLY INEFFECTIVE

• Athletic performance. Oral glutamine does not seem to improve athletic performance. Details: Small studies in trained athletes or healthy adults show that taking glutamine orally does not seem to enhance performance or immune response during intense acute or prolonged exercise when compared with placebo (2341,2342,5455,5456).
• Crohn disease. Oral glutamine does not seem to improve symptoms of this condition. Details: Small clinical studies in adults and children with Crohn disease show that taking glutamine 7 grams three times daily or following a glutamine-enriched diet for 4 weeks does not seem to improve intestinal permeability or disease activity, and might even worsen disease activity, when compared with placebo or a low-glutamine diet (2338,6256).
• Cystinuria. Oral glutamine does not seem to improve cystinuria. Details: According to case reports, taking glutamine orally does not seem to reduce the excretion of cysteine in the urine in patients with homozygous cystinuria (2339).
• Low birth weight. Oral glutamine does not seem to reduce adverse consequences of low birth weight in infants. Details: Most clinical studies show that glutamine supplementation does not improve the time to full enteral feeding, infant growth rate, or length of hospital stay in low birth weight infants (52305,52312,52325,52342,52362,52410). One follow-up study also shows that neonatal glutamine supplementation is not associated with improvements in cognitive function, motor skills, or behavior outcomes by school age when corrected for neonatal infection rate (52342,97365).
• Muscular dystrophy. Oral glutamine does not seem to improve symptoms of Duchenne muscular dystrophy. Details: Clinical studies show that taking glutamine 0.5-0.6 grams/kg orally does not significantly improve muscle strength or whole body protein degradation in children with Duchenne muscular dystrophy when compared with placebo or a nonspecific amino acid mixture (46657,52363).
• Prematurity. Oral glutamine does not seem to reduce morbidity or mortality associated with prematurity. Details: A meta-analysis of clinical trials in preterm infants, including infants with low to very low birth weight, shows that use of enteral or parenteral glutamine does not reduce the risk of mortality or morbidities, such as necrotizing enterocolitis, when compared with control. However, limited evidence from a sub-group analysis suggests that enteral glutamine might modestly reduce the risk of invasive infection when compared with control (105015). These findings are limited by the selection bias and heterogeneity of the included trials.
• Radiation-induced diarrhea. Oral glutamine does not seem to improve diarrhea due to radiation therapy. Details: One meta-analysis of five randomized, controlled trials shows that taking oral glutamine during radiotherapy for pelvic cancers does not prevent or reduce the severity of diarrhea when compared with placebo (97367).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Antiretroviral-associated diarrhea. It is unclear if oral glutamine improves diarrhea caused by antiretroviral agents. Details: A small crossover clinical study in HIV patients shows that oral glutamine 30 grams daily for 10 days seems to reduce the severity of nelfinavir-associated diarrhea when compared with placebo (52313).
• Alcohol use disorder. Although there is interest in using oral glutamine for alcohol use disorder, there is insufficient reliable information about the clinical effects of glutamine for this condition.
• Attention deficit-hyperactivity disorder (ADHD). Although there is interest in using oral glutamine for ADHD, there is insufficient reliable information about the clinical effects of glutamine for this condition.
• Chemotherapy-induced diarrhea. It is unclear if oral glutamine improves diarrhea caused by chemotherapy. Details: Although preliminary clinical studies show that glutamine might reduce the occurrence of chemotherapy-induced diarrhea (7235,7285), a meta-analysis of this research and others shows no difference in the severity of diarrhea (7233,7295,96516). Despite results showing a significant 1-day reduction in the duration of diarrhea, this might not be considered clinically significant (96516).
• Chemotherapy-induced lymphocytopenia. It is unclear if oral glutamine reduces lymphocytopenia caused by chemotherapy. Details: One small clinical study in patients with esophageal cancer receiving chemo-radiotherapy shows that taking glutamine 30 grams daily for 28 days seems to prevent a reduction in lymphocytes when compared with placebo (2705). However, another small clinical trial in patients with leukemia or lymphoma receiving intensive chemotherapy shows that adding glutamine 26 grams to total parenteral nutrition (TPN), in place of other amino acids, does not affect duration of neutropenia when compared with receiving an isonitrogenous standard TPN (7295).
• Coronavirus disease 2019 (COVID-19). It is unclear if oral glutamine is beneficial in patients hospitalized with COVID-19 pneumonia. Details: A very small, nonblinded, non-randomized evaluation of otherwise healthy patients over 50 years of age who were hospitalized with mild COVID-19 pneumonia shows that taking glutamine 10 grams three times daily orally with meals is associated with a 1-day decrease in hospital stay (from 10 days to 9) when compared with patients not taking glutamine. In the latter group, 4 patients required transfer to the ICU, compared with no patients in the glutamine group (103839). A similar, non-randomized evaluation of adults hospitalized with COVID-19 pneumonia shows that adding the same dose of glutamine to other therapies for 5 days is associated with a 3-day decrease in hospital stay (from 14 days to 11) when compared with patients not taking glutamine. At the end of treatment, 0% of patients in the glutamine group required ICU services, compared with 54% of patients who did not receive glutamine. This study also shows that taking glutamine may increase appetite (108035). The validity of these findings is limited by short duration of treatment and use of non-standardized treatments.
• Cystic fibrosis. It is unclear if oral glutamine improves growth and development in children with cystic fibrosis. Details: A small clinical study in undernourished or stunted children with cystic fibrosis shows that taking glutamine 0.7 grams/kg daily orally for 4 weeks with or without recombinant human growth hormone (rhGH) does not promote protein gain when compared with rhGH alone (52321).
• Diabetic foot ulcers. Oral glutamine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that taking a specific nutritional supplement drink containing glutamine 7 grams, arginine 7 grams, and hydroxymethylbutyrate 1.5 grams (Abound, Abbott) twice daily for 16 weeks does not improve total wound closure or reduce the time to complete healing when compared with a control drink in patients with diabetic foot ulcers (96637). It is unclear if this effect is due to glutamine, other ingredients, or the combination.
• Diarrhea. It is unclear if oral glutamine improves diarrhea in children and infants. Details: One preliminary clinical study in 6-24 month-old otherwise healthy children with acute diarrhea shows that taking capsules prepared with a specific glutamine powder (Power Glutamine, Champion Nutrition) 0.3 grams/kg daily for 7 days reduces the duration of diarrhea by about one day when compared with placebo (52323). However, other clinical research in male infants 1-12 months old with acute diarrhea and dehydration shows that adding glutamine 90 mmol/L along with the standard World Health Organization oral rehydration salts (ORS) does not decrease the duration of diarrhea, stool output, or the volume of oral rehydration solution required to achieve and maintain hydration when compared with standard ORS alone (7298).
• Hematopoietic stem cell transplant (HSCT). It is unclear whether oral glutamine or glutamine added to parenteral nutrition improves morbidity and mortality in patients undergoing HSCT. Some research has suggested that intravenous glutamine may actually worsen outcomes. Details: Some research suggests that patients receiving glutamine-supplemented parenteral nutrition (PN) after HSCT primarily to treat hematologic malignancies have a diminished incidence of clinical infections, lower rates of microbial colonization, and decreased length of hospital stay when compared to control (2366,52381). However, not all patients seem to benefit. Some research shows that oral glutamine or PN with glutamine does not reduce the risk of mortality or infections in patients with hematologic malignancies and/or solid tumors (5451,52385). Also, a small clinical study in patients undergoing HSCT shows that PN with glutamine dipeptide may increase the duration of hospital stay (52292). Furthermore, one small study has found that receiving PN with glutamine was associated with lower disease-free survival and event-free survival over 3 years when compared with standard PN in patients receiving HSCT for hematologic malignancies (52355).
• Irritable bowel syndrome (IBS). There is limited evidence on the oral use of glutamine in patients with IBS. Details: A clinical trial in adults with IBS (diarrhea-predominant, constipation-predominant, mixed, or alternating bowel habits) shows that following a low FODMAP diet supplemented with oral glutamine 15 grams three times daily for 6 weeks improves IBS-Severity Scoring System (IBS-SSS) scores, with 88% of patients in the glutamine group reporting a 45% improvement in severity scores, compared with 60% of patients following the low FODMAP diet alone (108037). The validity of this finding is limited by short duration of treatment and lack of follow-up. Preliminary clinical research in patients with postinfectious, diarrhea-predominant IBS shows that taking glutamine 5 grams three times daily for 8 weeks leads to a nearly 14-fold greater likelihood of symptom improvement, defined as a reduction of 50 points or more on the IBS-SSS, and decreases stool frequency by 2.45 stools daily when compared with placebo. Taking glutamine also seems to reduce abdominal pain ratings by 55% and improve quality of life scores by 53% when compared to baseline in these patients (100944). The validity of these findings is limited by the lack of a comparator group.
• Lung cancer. It is unclear if oral glutamine improves survival in patients with advanced lung cancer. Details: One small clinical study in patients with advanced non-small cell lung cancer shows that taking glutamine 10 grams three times daily for 12 months along with palliative chemoradiotherapy prevents weight loss, which is an important predictor of survival, but does not increase the likelihood of progression-free survival when compared with palliative chemoradiotherapy alone (100942). It is unclear if this study was adequately powered to detect a difference in survival between groups.
• Malnutrition. It is unclear if oral alanyl-glutamine improves height and weight in children at risk for malnutrition. Details: Preliminary clinical research in children aged 2 months to 5 years from a low-income area of Brazil and at risk for malnutrition, shows that taking 3-12 grams of alanyl-glutamine orally daily for 10 days improves gut integrity and is associated with a modest, short-term increase in weight when compared with a glycine placebo (103838).
• Exercise-induced muscle damage. It is unclear if oral glutamine is beneficial for exercise-induced muscle damage. Details: A very small clinical crossover trial in professional athletes undergoing rigorous training shows that taking oral glutamine 6 grams daily for 20 days reduces serum levels of creatine kinase and myoglobin when compared with placebo (108031). The validity of these findings is limited due to the small size and short duration of treatment.
• Obesity. It is unclear if oral glutamine is beneficial for weight loss. Details: A preliminary clinical study in 36 overweight or obese adults shows that taking glutamine 30 grams daily for 2 weeks reduces waist circumference by 1.8 cm, but does not improve body weight, body mass index, or glycemic indices, when compared to baseline. None of these outcomes were improved over baseline in an alanine control group (100941). Given the small study size and short duration of therapy, the long-term effects of glutamine on anthropometric measures is unclear.
• Opioid withdrawal. Oral glutamine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical study in Chinese patients undergoing detoxification from heroin shows that taking a combination of tyrosine, lecithin, 5-HTP, and glutamine 50 mg/kg orally daily for 6 days might reduce mood-related withdrawal symptoms when compared with placebo (88178). It is unclear if this effect is due to glutamine, other ingredients, or the combination.
• Oral mucositis. There is contradictory evidence about the effects of glutamine in patients with, or at risk of developing, oral mucositis from chemotherapy or radiotherapy. Details: Small clinical studies suggest that taking glutamine orally or swishing and swallowing a glutamine solution can decrease the incidence, severity, and duration of oral mucositis in some patients undergoing chemotherapy and/or radiation therapy for cancer or hematopoietic stem cell transplant (HSCT) (2336,2368,2704,5029). Additionally, three meta-analyses of highly heterogeneous clinical trials in patients with cancer receiving chemotherapy and/or radiation therapy suggests that glutamine reduces the incidence of severe (grade ≥3) oral mucositis when compared with control (105014,108028,108036). These analyses are limited for several reasons, including reporting bias, lack of sensitivity analysis, and population heterogeneity. Some small clinical studies included in these meta-analyses suggest that supplementation with glutamine may reduce the need for feeding tubes and opioid analgesics (108028,108036). However, not all research has been positive. Some small clinical studies in patients receiving chemotherapy with 5-fluorouracil for cancer or HSCT suggest that oral or intravenous glutamine does not reduce the incidence of oral mucositis when compared with control (2365,5451,5462,7296,52349,52350). Furthermore, a meta-analysis of 5 clinical trials in patients with head or neck cancers shows that oral glutamine does not reduce the overall incidence or the incidence of moderate to severe radiation-induced oral mucositis when compared with control (103836). The Multinational Association of Supportive Care in Cancer and the International Society for Oral Oncology (MASCC/ISOO) cautiously recommends the use of oral glutamine to prevent oral mucositis in patients with head and neck cancer receiving chemoradiotherapy. However, due to some evidence suggesting that intravenous glutamine may actually worsen outcomes in HSCT patients, the MASCC/ISOO recommends against its use for the prevention of oral mucositis in patients receiving high-dose chemotherapy, with or without total body irradiation, for HSCT (105004).
• Paclitaxel-induced myalgia and arthralgia. It is unclear if oral glutamine reduces the risk for myalgias and arthralgias due to paclitaxel. Details: One small clinical study shows that taking glutamine 10 grams three times daily for 5 days, starting on the day of chemotherapy and repeated over 2 cycles of chemotherapy, does not reduce the rate or severity of paclitaxel-induced myalgias or arthralgias when compared with placebo (52331).
• Pancreatitis. It is unclear if oral glutamine improves outcomes in patients with acute pancreatitis. Details: Two meta-analyses of the available clinical research in patients with pancreatitis show that enteral or parenteral supplementation with glutamine increases albumin, decreases C-reactive protein, and might reduce mortality, multiple organ dysfunction syndrome, hospital length of stay, and infections. Results are difficult to interpret due to the significant heterogeneity of the included trials and limited generalizability of the results (96513,103835).
• Peptic ulcers. Although there is interest in using oral glutamine for peptic ulcers, there is insufficient reliable information about the clinical effects of glutamine for this condition.
• Postoperative infection. It is unclear if oral or intravenous glutamine is beneficial for the prevention of postoperative infection in patients with colorectal cancer who are recovering from surgery. Details: A meta-analysis of nonblinded clinical research in adults with colorectal or colon cancer who recently underwent radical surgery shows that daily supplementation with glutamine 0.3-1 grams/kg, administered either orally or parenterally, improves the rate of surgical site infections and anastomotic leakage when compared with control (108033). These findings are limited by the high heterogeneity of the included studies and unclear reporting.
• Postoperative recovery. It is unclear if oral or intravenous glutamine is beneficial in patients with colorectal cancer who are recovering from surgery. Details: A meta-analysis of nonblinded clinical research in adults with colorectal or colon cancer who recently underwent radical surgery shows that taking either oral or parenteral glutamine 0.3-1 grams/kg daily may reduce the length of hospital stay when compared with control (108033). These findings are limited by the high heterogeneity of the included studies and unclear reporting.
• Pressure ulcers. Oral glutamine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A very small clinical study in patients with stages II-IV pressure ulcers shows that taking a specific nutritional supplement drink containing glutamine 7 grams, arginine 7 grams, and hydroxymethylbutyrate 1.5 grams per packet (Abound, Abbott Nutrition) as two packets twice daily by mouth for 2 weeks has no effect on wound area or healing scores by the Pressure Ulcer Scale for Healing (PUSH) measurement when compared with standard nutritional care (96506).
• Radiation dermatitis. It is unclear if oral glutamine reduces the risk of developing dermatitis from radiation therapy. Details: One small clinical study in patients with head and neck cancers receiving cisplatin shows that taking a specific supplement containing glutamine 7 grams, arginine 7 grams, and hydroxymethylbutyrate 1.5 grams (Abound, Abbott) orally twice daily, starting on day 1 of radiation and continuing until 1 week after radiation therapy, does not reduce the incidence of severe radiation-induced dermatitis when compared with no supplementation (96639). However, another small clinical study in patients with breast cancer who have had both chemotherapy and surgery shows that taking oral glutamine 5 grams three times daily, starting 1 week before radiation and continuing until 1 week after radiation, is associated with a reduction in grade 1 and grade 2 radiation dermatitis when compared with placebo (97366).
• Radiation-induced esophagitis. It is unclear if oral glutamine reduces the risk of developing esophagitis from radiation therapy. Details: A small clinical study in patients with advanced non-small cell lung cancer shows that taking glutamine 10 grams three times daily for 12 months along with a palliative dose of chemoradiotherapy (total 30 Gy) results in a 7% incidence of symptomatic (grade 2 or higher) radiation-induced esophagitis, compared with a 53% incidence with palliative chemoradiotherapy alone. The glutamine group also had a 5.8-day delay in the onset of esophagitis (100942). However, a lower dose of glutamine in patients receiving higher doses of radiotherapy might not be beneficial. A small clinical study in patients with advanced thoracic malignancies shows that taking glutamine 4 grams mixed in water twice daily for 4 weeks along with radiotherapy (total dose of at least 45 Gy) to the esophagus, with or without chemotherapy, does not slow the onset of radiation-induced esophagitis or reduce its severity when compared with a glycine placebo (105011).
• Short bowel syndrome. It is unclear if oral glutamine improves symptoms of short bowel syndrome. Details: Although small clinical studies suggest that glutamine plus growth hormone can decrease dependence on parenteral nutrition in some patients (2334,2361,2362,2703), it has not shown benefit for improving intestinal absorption of energy in all studies (8185). Additionally, glutamine alone doesn't appear to be beneficial (7730).
• Traumatic Brain injury (TBI). It is unclear if intravenous glutamine is beneficial in patients hospitalized with severe TBI. Details: A clinical trial in patients hospitalized for a severe TBI shows that adherence to a hypocaloric, low-protein diet supplemented with daily intravenous glutamine 0.3 g/kg for 7 days does not improve 28-day mortality when compared with standard nutritional support alone. However, it may reduce the length of ventilator use, hospitalization, and duration of intensive care unit stay (108034).
• Vincristine-induced neuropathy. It is unclear if oral glutamine reduces the risk of developing neuropathy from treatment with vincristine in children. Details: Preliminary clinical research in children ages 1-21 years receiving vincristine for various cancer types shows that taking glutamine 6 grams/m2 twice daily orally for 21 days reduces sensory neuropathy when compared with placebo. There was a significant improvement in self-reported, but not parent-reported, quality of life scores as measured by the PedsQL scale. However, there was no effect on motor neuropathy with the use of glutamine (96517).
• Wound healing. It is unclear if oral glutamine improves wound healing. Details: Preliminary clinical research in trauma patients with wound healing disorders shows that taking glutamine 20 grams orally daily in combination with ascorbic acid 500 mg, vitamin E 166 mg, beta-carotene 3.2 mg, selenium 100 mcg, and zinc 6.6 mg (Glutamine Plus, Fresenius Kabi) for 14 days reduces the time to wound closure by 29 days when compared with placebo. However, there is no difference in length of stay (97364). More evidence is needed to rate glutamine for these uses.

(Read more about GLUTAMINE)

EFFECTIVE

• Pyridoxine-dependent epilepsy. Intravenous vitamin B6 is effective for controlling pyridoxine-dependent seizures. Details: Pyridoxine-dependent seizures are a rare type of refractory seizures in neonates that do not respond to anticonvulsant drugs. These seizures are typically controlled within minutes of intravenous administration of pyridoxine, a form of vitamin B6. Pyridoxine-dependent seizures can be due to genetic (autosomal recessive) pyridoxine dependency, or more commonly, a result of the use of high-dose pyridoxine during pregnancy (8197,8198).
• Sideroblastic anemia. Oral vitamin B6 is effective for treating hereditary sideroblastic anemia. Details: Taking vitamin B6 (pyridoxine) orally is effective for treating hereditary sideroblastic anemia (15,9518). Taking the active form of vitamin B6 (pyridoxal-5'-phosphate) also seems to be effective in cases in which the patient does not respond to pyridoxine (93049).
• Vitamin B6 deficiency. Oral vitamin B6 is effective for preventing and treating vitamin B6 deficiency. Details: Taking oral vitamin B6 can prevent and treat vitamin B6 deficiency (15).

LIKELY EFFECTIVE

• Hyperhomocysteinemia. Taking vitamin B6 orally, alone or in combination with folic acid, is effective for reducing hyperhomocysteinemia. Details: Vitamin B6 (pyridoxine) seems to lower homocysteine concentrations when folic acid and vitamin B12 are at physiologic levels or when given with folic acid and vitamin B12 supplements (9451,83042,107136). A combination of vitamin B6 100 mg and folic acid 0.5 mg daily seems to lower homocysteine levels by about 35% and is recommended for people with postprandial hyperhomocysteinemia (1489,9406). Other research shows that taking pyridoxine 50-200 mg daily reduces postprandial homocysteine levels by 32% to 35% (9406,10350). Pyridoxine also seems to reduce homocysteine levels in patients with kidney failure, kidney transplant patients (1489,6884,9414,9415), or patients who receive general anesthesia with nitrous oxide (9481). However, some research in healthy adults suggests that adding pyridoxine to folic acid might not provide any additional benefit over folic acid alone (9400,9405,9409,50145). Hyperhomocysteinemia is considered by some to be an independent risk factor for atherosclerosis, recurrent thromboembolism, deep vein thrombosis, myocardial infarction, and ischemic stroke (1899,3323,9402,9405,9408,9409). However, elevated homocysteine levels may be a marker, as opposed to a cause, of vascular disease (11387,11388). A 5 µmol/L increase in plasma homocysteine increases the risk of cerebrovascular disease by 50% and the odds of coronary heart disease by 60% and 80% in males and females, respectively (9407,9411). However, it is not clear if reducing homocysteine levels results in reduced cardiovascular morbidity and mortality (1489,6883,6884,9308,9400,9405,9409). Folic acid, vitamin B6, and vitamin B12 supplementation can reduce total homocysteine from 13.4 to 11 µmol/L. However, this reduction does not seem to help with secondary prevention of death or myocardial infarction, and some research even suggests an increase in cardiovascular disease (CVD) risk (11387,13482,50423,83050,97619). There is also debate about whether supplementation with homocysteine-lowering B vitamins can reduce the risk of stroke. A number of large clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with CVD or impaired renal function (11387,13482,50423,83050,96150). However, a more recent meta-analysis shows that B vitamin supplementation modestly reduces the relative risk of stroke by 10% when compared with placebo in patients at risk for or with a history of CVD (97619). Also, a meta-analysis in patients with a history of stroke shows that B vitamin supplementation modestly reduces the relative risk of stroke recurrence by 13% and the risk of vascular death by 11% when compared with placebo (107136).

POSSIBLY EFFECTIVE

• Antipsychotic-induced hyperprolactinemia. It is unclear if oral vitamin B6 is beneficial for patients with antipsychotic-induced hyperprolactinemia. Details: Clinical research in male patients with hyperprolactinemia who are on a consistent antipsychotic dose shows that taking vitamin B6 300 mg twice daily for 16 weeks reduces serum prolactin levels by 68%, compared with 37% in patients taking aripiprazole 5 mg twice daily. Also, 67% of patients taking vitamin B6 had prolactin levels less than 40 mcg/mL versus 2% of those taking aripiprazole (107128).
• Kidney stones (nephrolithiasis). Oral vitamin B6 seems to decrease urinary oxalate levels and decrease the risk of kidney stone formation in some patients. Details: There is some evidence that taking vitamin B6 (pyridoxine) orally, alone or in combination with magnesium, can decrease urinary oxalate levels in people with type I primary hyperoxaluria, a hereditary disorder (1201,6437,6438,6439,6440,8548,8549,8550). Additionally, a small clinical study in this population suggests that intravenous pyridoxine hydrochloride can reduce urinary oxalate by 25.5% when compared to baseline (90796). In patients with idiopathic hyperoxaluria, taking a combination of pyridoxine 25mg and magnesium oxide 400 mg for 3 months decreases urinary oxalate by approximately 16%, with 68% of patients experiencing a reduction. However, supplementation is less effective than following a low-oxalate diet, which reduces urinary oxalate in 91% of patients by an average of 31% (107127). There is also preliminary evidence that higher pyridoxine intake in females with no history of kidney stones is associated with decreased risk of kidney stone formation (6441), but this association has not been found in males (6442).
• Pregnancy-induced nausea and vomiting. Oral vitamin B6 may reduce nausea and vomiting in some pregnant patients and is sometimes used in combination with doxylamine. Details: While some conflicting evidence exists, most small clinical studies suggest that oral vitamin B6 is effective for improving nausea and vomiting associated with pregnancy when compared with baseline or placebo. However, vitamin B6 may not be as effective as ginger (110459). Two small clinical studies show that taking vitamin B6 (pyridoxine) 25 mg every 8 hours for 3-4 days decreases pregnancy-induced nausea severity and vomiting incidence when compared with placebo (6168,16306). A larger clinical trial shows that taking lower doses of vitamin B6, 10 mg every 8 hours over 5 days, improves pregnancy-induced nausea, but not vomiting, when compared with placebo (6167). A small clinical study in patients with mild to moderate nausea and vomiting shows that taking a higher dose of 40 mg twice daily for 4 days is more effective than placebo, but no better than ginger 500 mg twice daily (99404). The American College of Obstetrics and Gynecology (ACOG) considers vitamin B6 at a dose of 10-25 mg 3 to 4 times daily a first-line treatment for pregnancy-induced nausea and vomiting due to its benign safety profile (111601). However, it is not effective for all patients, such as those with hyperemesis gravidarum, a severe form of pregnancy-induced nausea and vomiting. Adding vitamin B6 20 mg three times daily for 2 weeks to intravenous rehydration, metoclopramide, and thiamine seems to be no more effective than placebo for reducing vomiting in hyperemesis gravidarum (99405). Vitamin B6 is also sometimes used in combination with doxylamine. In fact, a combination of vitamin B6 plus doxylamine (Diclegis or Bonjesta, Duchesnay Inc., and various generics) has been approved by the US Food and Drug Administration (FDA) as a prescription product111601). ACOG recommends vitamin B6 in combination with doxylamine as another first-line treatment option (111601). However, the clinical trial used to obtain FDA approval has some methodological problems, and the significance of the results has been questioned. The improvement in symptom scores seen with Diclegis was less than one point on a 13-point scale, which is unlikely to be clinically significant (97998). Also, some clinical research shows that taking pyridoxine 25 mg and doxylamine 12.5 mg is less effective than ondansetron 4 mg when taken every 8 hours for 5 days. Only 41% of the patients using pyridoxine and doxylamine had a clinically significant reduction in nausea, compared to 92% of patients using ondansetron (90797). The combination of vitamin B6 and doxylamine is also studied with acupuncture. A large clinical study in patients with moderate to severe pregnancy-induced nausea and vomiting conducted in China shows that taking vitamin B6-doxylamine (Diclegis, Duchesnay, Inc) 20 to 40 mg each at bedtime for 14 days in combination with daily acupuncture modestly improves patient-reported nausea and vomiting scores when compared with either intervention alone (111820). However, it is unclear whether this improvement is clinically significant.
• Premenstrual syndrome (PMS). Oral vitamin B6 seems to reduce PMS symptoms. Details: There is some evidence that taking vitamin B6 (pyridoxine) orally can improve symptoms of PMS such as breast pain or tenderness (mastalgia) and depression in some patients. Pyridoxine in doses of at least 50 mg daily, plus magnesium oxide 200 mg daily, seems to relieve PMS-related anxiety and other symptoms (8555,39007,82962). Although some clinicians advocate doses of pyridoxine 200-500 mg daily for PMS, doses of 50-100 mg daily seem to work just as well. There is no apparent dose-response curve for PMS, so the lowest effective dose should be used. Higher doses might increase the risk of side effects (3093).

POSSIBLY INEFFECTIVE

• Age-related cognitive decline. Oral vitamin B6 does not seem to slow age-related cognitive decline. Details: One clinical trial in elderly people with memory complaints shows that taking a combination of B vitamins, including folic acid 0.8 mg, vitamin B12 0.5 mg, and vitamin B6 (form not specified) 20 mg daily for 24 months reduces cerebral atrophy in the gray matter regions associated with Alzheimer disease by up to seven-fold when compared with placebo. However, this protection does not occur in patients with the lowest average blood levels of homocysteine (90374). Furthermore, other clinical research shows that taking vitamin B6 (pyridoxine) 3-75 mg daily in combination with folic acid and vitamin B12 does not improve cognitive function in elderly adults (14392,50225,50510).
• Alzheimer disease. Oral vitamin B6 does not seem to improve cognitive function in patients with Alzheimer disease when used in combination with other B vitamins. Also, oral vitamin B6 does not seem to reduce the risk of developing this condition. Details: Clinical research in patients with probable Alzheimer disease taking routine medications shows that taking vitamin B6 25 mg with folic acid 5 mg and vitamin B12 1 mg daily for 18 months does not have a beneficial effect on cognitive function or the severity of disease when compared with placebo. In this study, all patients were consuming a folate-fortified diet (50319). Also, population research in elderly adults has found that a high intake of vitamin B6 from dietary or supplemental sources is not associated with a decreased risk of Alzheimer disease when compared to lower vitamin B6 intake (13165,15270).
• Carpal tunnel syndrome. Oral vitamin B6 does not seem to reduce symptoms of carpal tunnel syndrome. Details: Most research shows that people with carpal tunnel syndrome are not generally deficient in vitamin B6 and do not benefit from taking vitamin B6 supplements (8203,8937,9448,9450,9478,9482). Although early studies by a single group of researchers, as well as anecdotal reports, suggest that taking vitamin B6 may relieve carpal tunnel symptoms, more reliable research has not supported these findings (8202,9445,9447,9449,9483,15955,83086). Vitamin B6 has also been evaluated in combination with other ingredients. A moderate-sized clinical study in adults with mild to moderate carpal tunnel syndrome shows that taking a combination product containing vitamin B6, alpha-lipoic acid, acetyl-L-carnitine, phosphatidylserine, turmeric, and vitamins C, E, B1, B2, and B12 twice daily for 60 days reduces symptom severity and pain but does not improve measures of hand and wrist function when compared with a control (111702). The dose of vitamin B6 was not provided. The validity of this study is limited by the lack of blinding and placebo. Additionally, it is unclear if the effects are due to vitamin B6, other ingredients, or the combination.
• Cataracts. Oral vitamin B6 does not seem to slow cataract development. Details: Clinical research in females with existing cardiovascular disease (CVD) or at increased risk of CVD shows that taking a combination of folic acid 2.5 mg, vitamin B6 (form not specified) 50 mg, and vitamin B12 1 mg daily for an average of 7.3 years does not reduce the risk of cataracts when compared with placebo. Furthermore, the risk of cataract extraction was increased by 28% (96149).
• Chemotherapy-induced acral erythema. While some conflicting evidence exists, most research suggests that oral or topical vitamin B6 does not seem to prevent or reduce the severity of acral erythema induced by chemotherapy. Details: A meta-analysis of 10 clinical trials and 4 observational studies shows that taking vitamin B6 60-500 mg daily for up to 8 chemotherapy cycles does not prevent chemotherapy-induced acral erythema or reduce the incidence of severe cases when compared with control. Most studies used capecitabine chemotherapy alone or in combination, and one study used pegylated liposomal doxorubicin; however, no subgroup analysis was conducted to differentiate chemotherapy regimens. Results did not seem to vary based on study location, study design, or vitamin B6 dose (104930). However, a more recent preliminary clinical study in patients receiving doxorubicin for multiple myeloma shows that taking vitamin B6 100 mg on the first day of chemotherapy then twice daily for 7 days with each cycle reduces the risk of developing acral erythema by 72%, but does not improve the severity of acral erythema, when compared with no vitamin B6 supplementation (110458). Also, one small, low-quality clinical study suggests that taking vitamin B6 400 mg daily reduces the risk of moderate or severe chemotherapy-induced acral erythema when compared with vitamin B6 200 mg daily; however, the higher dose also seems to be associated with worsened tumor response and increased treatment failure (97620). Topical vitamin B6 has also failed to show benefit. A small clinical study in patients with acral erythema from capecitabine or pegylated liposomal doxorubicin shows that applying vitamin B6 1% cream to affected areas three times daily for 6 weeks does not improve symptoms when compared with placebo (104929).
• Colorectal adenoma. Oral vitamin B6 does not seem to reduce the risk of developing colorectal adenomas. Details: Clinical research shows that taking a combination of B vitamins, including folic acid 2.5 mg, vitamin B6 (pyridoxine) 50 mg, and vitamin B12 1 mg, daily for up to 9.2 years does not reduce the risk of colorectal adenoma in females at high risk of cardiovascular disease when compared with placebo (90389).
• Eclampsia. Oral or intramuscular vitamin B6 does not seem to reduce the risk of eclampsia. Details: Meta-analyses of limited clinical research in pregnant patients show that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of eclampsia when compared with control (83046,96166).
• Osteoporosis. Oral vitamin B6 does not seem to reduce the risk of osteoporotic fractures. Details: Clinical research in patients with cerebrovascular disease shows that taking a combination of B vitamins, including folic acid 2 mg, vitamin B6 (form not specified) 25 mg, and vitamin B12 500 mcg daily for up to 10.5 years does not prevent osteoporotic fractures when compared with placebo (90377). Furthermore, a secondary analysis of two large studies in patients with cardiovascular disease has found that taking vitamin B6 (pyridoxine) 40 mg daily in addition to folic acid and vitamin B12 for 1-3 years is associated with a 42% increased risk of hip fracture over an 11-year period when compared with only folic acid and vitamin B12 (96163). This finding is limited because these studies were not designed to assess the effects of vitamin B6 on fracture risk and the analyses were not adjusted for baseline bone health or fall risk.
• Pre-eclampsia. Oral or intramuscular vitamin B6 does not seem to reduce the risk of pre-eclampsia. Details: Meta-analyses of limited clinical research in pregnant patients show that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of pre-eclampsia when compared with placebo (83046,96166).
• Preterm labor. Oral or intramuscular vitamin B6 does not seem to reduce the risk of preterm labor. Details: Meta-analyses of limited clinical research in pregnant patients shows that taking vitamin B6 (pyridoxine), either as 25 mg daily or a single dose of 100 mg orally or intramuscularly, does not reduce the risk of preterm labor when compared with placebo (83046,96166).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Acne. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in adults and children with inflammatory acne shows that taking 1-4 tablets of a specific product (NicAzel, Elorac Inc.) containing vitamin B6 (pyridoxine), nicotinamide, azelaic acid, zinc, copper, and folic acid for 8 weeks reduces inflammatory lesions and improves appearance in 88% and 81% of patients, respectively, when compared to baseline (90800). The validity of these findings is limited by the lack of a comparator group.
• Age-related macular degeneration (AMD). Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A large-scale clinical study shows that taking vitamin B6 (pyridoxine) 50 mg, vitamin B12 1000 mcg, and folic acid 2.5 mg daily reduces the risk for AMD in females over 40 years of age with a history of cardiovascular disease (CVD) or with risk factors for CVD. Those who took this combination for an average of 7.3 years had a 34% reduced risk of developing AMD and a 41% reduced risk of visually significant AMD when compared with placebo (14620). It is unclear if this effect is due to vitamin B6, other ingredients, or the combination.
• Angioplasty. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Some evidence suggests that vitamin B6 (pyridoxine) 10 mg, folic acid 1 mg, and vitamin B12 400 mcg daily can decrease the rate of restenosis in patients treated with balloon angioplasty (8009,9412). However, this combination does not seem to be as effective for reducing restenosis in patients after coronary stenting (8009). An intravenous loading dose of folic acid, vitamin B6 (pyridoxine), and vitamin B12 followed by oral administration of folic acid 1.2 mcg, vitamin B6 (pyridoxine) 48 mg, and vitamin B12 60 mcg daily after bare metal coronary stenting also does not seem to reduce restenosis and might actually increase restenosis (12150,12151). Due to the lack of evidence of benefit and potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents (12151). It is unclear if any effects are due to vitamin B6, other ingredients, or the combination.
• Antipsychotic-induced metabolic side effects. It is unclear if oral vitamin B6, as an adjunct to progesterone, is beneficial in patients with antipsychotic-induced amenorrhea. Details: A small clinical study in females with antipsychotic-induced amenorrhea shows that taking vitamin B6 80 mg three times daily for 1 month plus intramuscular progesterone daily for 5 days increases levels of estradiol and follicle stimulating hormone, reduces prolactin levels, and increases the rate of clinical efficacy, defined as the normalization of menstruation and improvement in endocrine indicators, by 14% when compared with progesterone alone (110457).
• Anxiety. It is unclear if oral vitamin B6 is beneficial in patients with anxiety. Details: Clinical research in college students shows that taking vitamin B6 100 mg daily for one month does not reduce anxiety scores when compared with placebo (110453). However, because a diagnosis of anxiety was not a requirement for study participation, it is unclear if these findings can be generalized to patients diagnosed with anxiety.
• Asthma. It is unclear if oral vitamin B6 is beneficial in patients with asthma. Details: Preliminary clinical studies show that taking vitamin B6 (pyridoxine) 200-300 mg daily may improve symptoms of asthma in some patients, but not others, when compared with placebo (7064,7065). Studies have yielded conflicting results, with some research suggesting that it may only be beneficial in children with severe asthma (7065). Additionally, some research suggests that theophylline may lower vitamin B6 levels, although it is unclear if vitamin B6 supplementation is beneficial (4522,7066,9503).
• Atherosclerosis. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in patients with intermediate risk for coronary heart disease shows that taking a specific supplement (Kyolic, Total Heart Health, Formula 108, Wakunga) containing vitamin B6 12.5 mg, aged garlic extract 250 mg, vitamin B12 100 mcg, folic acid 300 mcg, and L-arginine 100 mg daily for 12 months reduces coronary artery calcium progression when compared with placebo (88385). It is unclear if this effect is due to vitamin B6, other ingredients, or the combination.
• Atopic dermatitis (eczema). It is unclear if oral vitamin B6 is beneficial in patients with eczema. Details: A small clinical study in children with eczema shows that taking vitamin B6 (pyridoxine hydrochloride) 50 mg daily for 4 weeks does not reduce symptoms such as redness and itchiness when compared with placebo (83090).
• Attention deficit-hyperactivity disorder (ADHD). It is unclear if oral vitamin B6 is beneficial for ADHD. Details: A small crossover study in children with ADHD shows that taking vitamin B6 600 mg, niacinamide and ascorbic acid 3 grams, and calcium pantothenate 1.2 grams daily for 6 weeks does not improve behavior scores when compared with placebo (9957).
• Autism spectrum disorder. Although there is interest in using oral vitamin B6 for autism, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Bipolar disorder. It is unclear if oral vitamin B6 is beneficial in patients with bipolar disorder. Details: A small clinical trial in patients with type 1 bipolar disorder who are taking lithium and experiencing an acute episode of mania shows that taking vitamin B6 80 mg daily for 8 weeks does not improve cognitive function or the severity of mania when compared with placebo. Cognitive function was reduced in patients taking vitamin B6; any effect on sleep was unclear (107132).
• Cancer. It is unclear if oral vitamin B6 reduces overall cancer risk. Details: Population research has found that higher dietary intake of vitamin B6 is associated with a 22% reduced risk of cancer, including esophageal, pancreatic, gastric, colorectal, and breast cancer. However, when dietary and supplemental vitamin B6 intake is considered, the inverse association between vitamin B6 and cancer risk is weaker and limited to fewer tumor sites. Furthermore, a meta-analysis of 9 clinical studies shows that taking vitamin B6 3-100 mg orally daily for 2-7.3 years, in combination with vitamin B12 and folate, does not reduce the risk of cancer in patients with cardiovascular disease or kidney failure (96164).
• Cardiovascular disease (CVD). Oral vitamin B6, taken along with other B vitamins, does not seem to improve secondary prevention of death or myocardial infarction in patients with CVD. However, it might slightly lower the risk of stroke. Details: Overall evidence from clinical research and meta-analyses shows that taking vitamin B6 in combination with folic acid and/or vitamin B12 does not seem to help with secondary prevention of death or myocardial infarction in patients with or at risk for CVD (11387,13482,34540,50423,83050,90379,97619). In fact, some research suggests that long-term supplementation with vitamin B6, folic acid, and vitamin B12 for secondary prevention increases the risk of CVD by 20% despite lowering homocysteine levels by 30% (13482). However, some research shows that taking vitamin B6 in combination with other B vitamins modestly reduces the risk of stroke, although results are conflicting (11387,13482,50423,83050,96150,96165,97619,107136). Additionally, it is unclear which specific combination of B vitamins is optimal for reducing stroke risk and which patients are most likely to benefit. In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) approved a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368).
• Cognitive function. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A moderate-sized clinical study in healthy adults aged 40-65 years shows that taking a supplement containing vitamin B6, ginkgo leaf, bacopa, and other B vitamins twice daily for 12 weeks does not improve memory or attention when compared with placebo (111334).
• Colorectal cancer. It is unclear if oral vitamin B6 reduces the risk of colorectal cancer. Details: A meta-analysis of observational studies suggests that the highest dietary intake of vitamin B6 is associated with a 20% reduced risk of colorectal cancer when compared with the lowest dietary intake. However, this association was not shown in subgroup analyses of studies conducted in Australia, Europe, or North America (111600). The validity of this analysis is limited by the heterogeneity of the included studies.
• Dental caries. There is limited evidence on the oral use of vitamin B6 for dental decay during pregnancy. Details: Meta-analyses of limited clinical research show that taking vitamin B6 (pyridoxine), 25 mg daily or a single dose of 100 mg orally or intramuscularly, may reduce the risk of dental decay during pregnancy when compared with placebo (83046,96166).
• Depression. It is unclear if oral vitamin B6 reduces the risk of developing depression or improves symptoms of depression. Details: Clinical research in healthy college students shows that taking vitamin B6 100 mg daily for one month does not reduce depression scores when compared with placebo (1104453). However, because a diagnosis of depression was not a requirement for study participation, it is unclear if these findings can be generalized to patients diagnosed with depression. Whether vitamin B6 reduces the risk of developing depression is also unclear. A meta-analysis of population research has found that the highest dietary intake of vitamin B6 is associated with a 19% lower risk of depression when compared with the lowest intake. However, sub-analyses suggest that this association is only relevant in females and not males (107133). In one individual population study in community dwelling older adults included in the analysis, the consumption of at least 1.71 mg of vitamin B6 daily from food was associated with a 43% reduction in the likelihood of becoming depressed when compared with the consumption of 1.33 mg or less daily in females. However, there was no association between vitamin B6 levels and risk of depression in males, and the finding in females was no longer significant when adjusted for total energy intake, since foods rich in vitamin B6 are energy-dense (96168). Another observational longitudinal study in healthy adults starting oral contraceptives containing ethinyl estradiol and levonorgestrel has found that taking vitamin B6 25 mg daily for 6-12 months is associated with a 40% lower risk of depression when compared with no supplementation (90789). Most available studies are cross-sectional in nature, making any conclusions related to causation difficult.
• Diabetes. It is unclear if oral vitamin B6 is beneficial in patients with type 2 diabetes or gestational diabetes. Details: Observational research in Chinese adults with type 2 diabetes has found that dietary intake of vitamin B6 in the highest quartile is associated with 53% lower odds of developing cardiovascular disease, defined as a non-fatal myocardial infarction, non-fatal stroke, or hospitalization for unstable angina, when compared with vitamin B6 intake in the lowest quartile (110452). Small clinical studies in patients with gestational diabetes and vitamin B6 deficiency shows that taking vitamin B6 (pyridoxine) 100 mg daily for 2 weeks improves glucose tolerance and blood glucose levels when compared with baseline (82967,83088). However, there is concern that these findings were confounded by dietary alterations. This benefit was not observed in a subsequent small case series in patients with gestational diabetes (22380).
• Diabetic neuropathy. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research suggests that taking a combination of B vitamins, including folic acid (L-methylfolate), vitamin B12 (methylcobalamin), and vitamin B6 (pyridoxal-5'-phosphate) for 24 weeks does not improve neural dysfunction based on vibration perception when compared with placebo in patients with diabetic neuropathy. However, taking this combination appears to modestly improve neuropathy symptoms and quality of life related to mental functioning when compared with placebo (90375).
• Dysmenorrhea. It is unclear if oral vitamin B6 is beneficial in patients with dysmenorrhea. Details: Preliminary clinical research shows that taking vitamin B6 (form not specified) 200 mg daily reduces pain associated with dysmenorrhea when compared with placebo. However, taking vitamin B6 in combination with magnesium does not reduce pain when compared with placebo (77388).
• Fibromyalgia. It is unclear if oral vitamin B6 is beneficial in patients with fibromyalgia. Details: A small clinical study in patients with fibromyalgia shows that taking vitamin B6 80 mg daily for 8 weeks does not improve pain, disease severity, anxiety, depression, or quality of life when compared with placebo (110454).
• Gastroenteritis-associated nausea and vomiting. It is unclear if oral vitamin B6 is beneficial in children with gastroenteritis. Details: A small clinical study in children aged 6 months to 12 years with acute viral gastroenteritis shows that taking vitamin B6 (form not specified) does not improve symptoms of dehydration or the frequency of vomiting when compared with placebo (90793).
• Helicobacter pylori. It is unclear if oral vitamin B6 is beneficial for Helicobacter pylori. Details: A large clinical study in adults with Helicobacter pylori infection shows that taking vitamin B6 20 mg twice daily for 2 weeks alongside conventional quadruple therapy does not improve eradication rates when compared with a control group not receiving vitamin B6 (113551). Conventional therapy consisted of a proton pump inhibitor, bismuth, minocycline, and metronidazole. The validity of this study is limited by the lack of placebo and inadequate blinding.
• Hypertension. It is unclear if oral vitamin B6 reduces blood pressure. Details: One small clinical study in patients with essential hypertension shows that taking vitamin B6 (pyridoxine hydrochloride) 5 mg/kg daily for 4 weeks can reduce systolic and diastolic blood pressure when compared with baseline (83091). The validity of this finding is limited by the lack of a control group.
• Hypertriglyceridemia. It is unclear if oral vitamin B6 reduces triglyceride levels. Details: Preliminary clinical research shows that vitamin B6 (form not specified) 50 mg daily for 12 weeks does not reduce triglyceride levels in people with hypertriglyceridemia when compared with placebo. However, vitamin B6 appears to decrease total cholesterol and high-density lipoprotein (HDL) cholesterol by approximately 9% in these patients (59028).
• Infertility. Although there is interest in using oral vitamin B6 for infertility, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Insomnia. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in healthy adults with self-reported sleep difficulty shows that taking a specific product (LZ Complex3, Sanofi Consumer Healthcare Pty Ltd.) containing vitamin B6, zizyphus extract, hops extract, hydrolyzed milk protein (Lactium), and magnesium oxide nightly, 30 minutes before bed, for 2 weeks does not improve sleep quality, daytime functioning, or physical fatigue when compared with placebo. However, due to the large improvement seen in both the treatment and placebo groups, the effectiveness of this product is unclear (95971).
• Isoniazid-induced neuropathy. It is unclear if oral vitamin B6 prevents the development of neuropathy in patients taking isoniazid. Details: Preliminary clinical research in patients taking isoniazid for tuberculosis shows that taking vitamin B6 (pyridoxine) 6 mg daily reduces the development of neuropathy when compared with control (83068).
• Lactation. It is unclear if oral vitamin B6 helps to suppress postpartum lactation. Details: A meta-analysis of two small clinical trials shows that taking vitamin B6 (pyridoxine) 400-600 mg daily for 6-7 days postpartum does not suppress lactation when compared with no treatment (83047).
• Levetiracetam-induced side effects. While some conflicting evidence exists, several small, low-quality studies suggest that oral vitamin B6 (pyridoxine) may reduce some neuropsychiatric adverse effects related to the use of levetiracetam. Details: In an analysis of case reports, retrospective studies, and a single low-quality prospective study, improvement in levetiracetam-associated neuropsychiatric symptoms occurred in approximately 73% of patients taking pyridoxine (107137). A more recent preliminary clinical trial in children ages 1-17 years shows that taking pyridoxine 10 or 15 mg/kg daily as needed based on symptoms improves behavioral side effects associated with levetiracetam by a small amount when compared with low-dose pyridoxine 0.5 mg/kg daily used as placebo (107124). Also, observational research in children ages 9 months to 14 years has found that taking vitamin B6 is associated with improved behavior and a 44% lower risk of levetiracetam discontinuation when compared with no vitamin B6 supplementation (110455). Some observational research in adults with levetiracetam-associated irritability has found that taking vitamin B6 is associated with an improvement in irritability in 45% of patients when compared to baseline (107129). However, a small clinical trial in adults with epilepsy shows that taking pyridoxine 40 mg daily for 3 weeks does not improve levetiracetam-related psychiatric adverse effects when compared with placebo (110456). This study may have been underpowered to detect differences between groups. Pyridoxine doses used in the studies above have ranged from 50-400 mg daily in children and 40-600 mg daily in adults (107124,107129,107137,110456).
• Lung cancer. It is unclear if dietary or oral vitamin B6 reduces lung cancer risk. Details: Epidemiological research has found that higher serum levels of vitamin B6 in male smokers is associated with a lower risk of lung cancer (9454). Also, people with blood levels of vitamin B6 in the top quartile have a modestly lower risk of lung cancer when compared with those whose levels are in the lowest quartile. The association is stronger for males and for people who have smoked (97999). However, other epidemiological research found that increased dietary intake of vitamin B6 is not associated with a reduced risk of lung cancer (96164).
• Menopausal symptoms. Although there is interest in using oral vitamin B6 for menopausal symptoms, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Motion sickness. Although there is interest in using oral vitamin B6 for motion sickness, there is insufficient reliable information about the clinical effects of vitamin B6 for this condition.
• Nausea and vomiting. It is unclear if oral vitamin B6 is beneficial for nausea and vomiting in patients taking oral contraceptives or antibiotics for Helicobacter pylori. Details: A large clinical study in adults with Helicobacter pylori infection shows that taking vitamin B6 20 mg twice daily for 2 weeks alongside conventional quadruple therapy reduces the incidence and severity of gastrointestinal adverse effects when compared with a control group not receiving vitamin B6 (113551). Conventional therapy consisted of a proton pump inhibitor, bismuth, minocycline, and metronidazole. The validity of this study is limited by the lack of placebo and inadequate blinding. An observational longitudinal study in healthy females taking oral contraceptives containing ethinyl estradiol and levonorgestrel has found that taking vitamin B6 25 mg daily for 6-12 months is associated with a 43% reduced risk of nausea when compared with no supplementation (90789).
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral vitamin B6 for patients with NAFLD. Details: A small clinical trial in patients with NAFLD shows that taking vitamin B6 (pyridoxine) 30 mg three times daily for 12 weeks does not reduce levels of liver transaminases or plasma lipids when compared with baseline. However, hepatic fat accumulation was modestly reduced (107130). The validity of this study is limited by the lack of a comparator group.
• Obesity. It is unclear if oral vitamin B6 in beneficial in overweight or obese individuals. Details: A small clinical trial in females with a body mass index (BMI) of at least 25 kg/m² shows that taking vitamin B6 as pyridoxine 80 mg daily for 8 weeks reduces fat mass and improves insulin resistance and triglyceride levels by a small amount when compared with placebo. Although some other anthropometric and metabolic indices were improved when compared with baseline, there was no effect of pyridoxine on body weight, visceral adiposity, or other endpoints when compared with placebo (107131).
• Overall mortality. It is unclear if oral vitamin B6 reduces the risk of overall mortality. Details: Observational research in US adults has found that dietary intake of vitamin B6 in the highest quintile is associated with a 12% to 21% lower risk of all-cause mortality and a 31% to 44% lower risk of cardiovascular mortality when compared with the lowest quintile of dietary vitamin B6 intake (110451).
• Pancreatic cancer. It is unclear if oral vitamin B6 reduces the risk of pancreatic cancer. Details: Observational research has found that higher dietary intake of vitamin B6 is associated with a 37% lower risk of developing pancreatic cancer when compared with lower intake (104927).
• Postpartum depression. It is unclear if oral vitamin B6 is beneficial in patients with postpartum depression. Details: Preliminary clinical research in individuals considered at increased risk for postpartum depression, but without clinical depression, shows that taking vitamin B6 80 mg daily from the 28th week of pregnancy until birth, and then 40 mg daily for one month, reduces symptoms of depression 1.5 months after birth when compared with baseline (measured during the third trimester) and when compared with placebo. However, it is unclear if any of the patients included in the study developed postpartum depression, as there were no changes in overall symptoms in patients taking placebo (107126).
• Proton pump inhibitor-induced gastrointestinal (GI) symptoms. It is unclear if oral vitamin B6 is beneficial for proton pump inhibitor-induced GI symptoms. Details: A large clinical study in adults with Helicobacter pylori infection shows that taking vitamin B6 20 mg twice daily for 2 weeks alongside conventional quadruple therapy reduces the incidence and severity of gastrointestinal adverse effects when compared with a control group not receiving vitamin B6 (113551). Conventional therapy consisted of a proton pump inhibitor, bismuth, minocycline, and metronidazole. The validity of this study is limited by the lack of placebo and inadequate blinding.
• Restless legs syndrome (RLS). It is unclear if oral vitamin B6 is beneficial in patients with RLS. Details: A small clinical study in adults with RLS who are beginning treatment with pramipexole shows that also taking vitamin B6 40 mg daily for 2 months moderately improves RLS scores and sleep quality scores when compared with pramipexole and placebo (110052).
• Schizophrenia. It is unclear if oral vitamin B6 is beneficial for patients with treatment-resistant schizophrenia. Details: Clinical research in male patients with treatment-resistant schizophrenia who are on a consistent antipsychotic dose shows that adding vitamin B6 300 mg twice daily for 16 weeks modestly improves psychotic symptoms and some measures of cognitive performance when compared with adding aripiprazole 5 mg twice daily (107128). More research is needed to determine if these benefits are clinically relevant.
• Seizures. It is unclear if oral vitamin B6 is beneficial for preventing seizures in patients with glycosylphosphatidylinositol (GPI) deficiency. Details: Observational case series in a small number of children and young adults with GPI deficiency has found that taking vitamin B6 20-30 mg/kg daily for 3-12 months is associated with some reduction in seizure frequency in 9 of 13 patients. However, no patient reached seizure freedom (107125,107135). In one case series, treatment for 12 months was associated with modest developmental improvements in almost all patients (107135). The study patient populations were slightly different in terms of age and underlying genetic causes for GPI deficiency.
• Sickle cell disease. Oral vitamin B6 has only been evaluated in combination with other B vitamins; its effect when used alone is unclear. Details: Preliminary clinical research in adults with sickle cell disease shows that taking vitamin B6 4.2-6 mg, vitamin B12 4.2-6 mcg, and folic acid 700 mcg daily might lower homocysteine levels. However, it is unknown if this will reduce the risk of endothelial damage in these patients (9324).
• Stroke. It is unclear if oral vitamin B6, either alone or with other B vitamins, is beneficial for stroke prevention. Details: There is some debate about whether supplementation with homocysteine-lowering B vitamins, including vitamin B6, can reduce the risk of stroke. A number of clinical studies and meta-analyses show that supplementation with folic acid, vitamin B6, and vitamin B12, alone or in combination, does not reduce the risk of stroke in patients with cardiovascular disease (CVD) or impaired kidney function (11387,13482,50423,83050,96150). However, a more recent meta-analysis of 10 clinical trials, including over 44,000 patients at risk for or with a history of CVD, shows that B vitamin supplementation reduces the relative risk of stroke by 10% when compared with placebo (97619). This meta-analysis differed from some of the earlier analyses due to the inclusion of several additional clinical trials. Also, another meta-analysis of three clinical trials including 9900 patients with a history of stroke shows that B vitamin supplementation reduces the relative risk of stroke recurrence by 13% when compared with placebo, although this finding was determined to have a low level of certainty. Based on two clinical trials, there was also a 17% reduced risk of vascular death and an 11% reduction in the combined risk of stroke, myocardial infarction, and vascular death (107136). In 2001, prior to the publication of the highest quality research on this topic, the US Food and Drug Administration (FDA) allowed a qualified health claim stating that, as part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6, and vitamin B12 may reduce the risk of vascular disease (102368). Unfortunately, even after the publication of higher quality research, it is still unclear which specific combination of B vitamins is optimal and which patients are most likely to benefit. One network meta-analysis shows that a combination of folic acid and vitamin B6 lowers the risk of stroke more effectively than B vitamin mixtures that include vitamin B12 (96165). However, this analysis is limited because it didn't account for dosing. Exposure to low, but not high amounts, of vitamin B12 (cyanocobalamin) seems to reduce stroke risk (96150).
• Tardive dyskinesia. It is unclear if oral vitamin B6 prevents tardive dyskinesia in patients taking neuroleptic drugs. Details: A small clinical study in patients taking neuroleptic drugs for schizophrenia shows that taking vitamin B6 (form not specified) 400 mg daily seems to improve Parkinsonian, dystonic, and dyskinetic symptoms when compared with placebo (8558).
• Tourette syndrome. Oral vitamin B6 has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small, nonblinded clinical study in children aged 4-17 years with untreated Tourette syndrome or with chronic tic disorder and associated symptoms of anxiety shows that taking a liquid nutritional supplement providing vitamin B6 2.8 mg and L-theanine 200 mg daily for 2 months improves scores on the Yale Global Tic Severity Scale, but does not reduce anxiety, when compared with patients receiving psychoeducation (108555). This study may have been inadequately powered to detect a difference between groups.
• Vincristine-induced neuropathy. Oral vitamin B6 has only been evaluated in combination with pyridostigmine; its effect when used alone is unclear. Details: A small clinical study in children ages 11 months to 13 years with neuropathy due to vincristine treatment for acute lymphoblastic leukemia, shows that taking vitamin B6 150 mg/m2 and pyridostigmine 3 mg/kg twice daily for 3 months is associated with reduced severity of sensory and motor neuropathy when compared with baseline (104928). The validity of this finding is limited by the lack of a control group. More evidence is needed to rate vitamin B6 for these uses.

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LIKELY SAFE ...when used orally and appropriately. Glutamine has been safely used in clinical research in doses up to 40 grams per day or 1 gram/kg daily (2334,2337,2338,2365,5029,5462,7233,7288,7293), (52288,52307,52308,52311,52313,52337,52349,52350,96516,97366). A specific glutamine product (Endari) is approved by the US Food and Drug Administration (FDA) (96520). ...when used intravenously. Glutamine has been safely incorporated into parenteral nutrition in doses up to 600 mg/kg daily in clinical trials (2363,2366,5448,5452,5453,5454,5458,7293,52272,52275), (52283,52289,52304,52306,52316,52341), (52359,52360,52371,52377,52381,52284,52385,52408,96637,96507,96516).

CHILDREN: LIKELY SAFE
when used orally and appropriately. Glutamine has been shown to be safe in clinical research when used in amounts that do not exceed 0.7 grams/kg daily in children 1-18 years old (11364,46657,52321,52323,52363,86095,96517). A specific glutamine product (Endari) is approved by the US Food and Drug Administration for certain patients 5 years of age and older (96520). ...when used intravenously. Glutamine has been safely incorporated into parenteral nutrition in doses up to 0.4 grams/kg daily in clinical research (52338,96508). There is insufficient reliable information available about the safety of glutamine when used in larger amounts in children.

PREGNANCY AND LACTATION: LIKELY SAFE
when consumed in amounts commonly found in foods. There is insufficient reliable information available about the safety of glutamine when used in larger amounts as medicine during pregnancy or lactation.

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LIKELY SAFE ...when used orally and appropriately in doses that do not exceed the tolerable upper intake level (UL) of 100 mg daily in the form of pyridoxine for adults (15,6243). ...when used parenterally and appropriately. Injectable vitamin B6 (pyridoxine) is an FDA-approved prescription product (15).

POSSIBLY SAFE ...when used orally and appropriately in doses of 101-200 mg daily (6243,8558).

POSSIBLY UNSAFE ...when used orally in doses at or above 500 mg daily. High doses, especially those exceeding 1000 mg daily or total doses of 1000 grams or more, pose the most risk. However, neuropathy can occur with lower daily or total doses (6243,8195). ...when used intramuscularly in high doses and frequency due to potential for rhabdomyolysis (90795).

CHILDREN: LIKELY SAFE
when used orally and appropriately in doses that do not exceed the tolerable upper intake level (UL) of vitamin B6 in the form of pyridoxine 30 mg daily for children aged 1-3 years, 40 mg daily for 4-8 years, 60 mg daily for 9-13 years, and 80 mg daily for 14-18 years (6243).

CHILDREN: POSSIBLY SAFE
when used orally and appropriately in amounts exceeding the recommended dietary allowance (5049,8579,107124,107125,107135).

CHILDREN: POSSIBLY UNSAFE
when used orally in excessive doses, long-term (6243).

PREGNANCY: LIKELY SAFE
when used orally and appropriately. A special sustained-release product providing vitamin B6 (pyridoxine) 75 mg daily is FDA-approved for use in pregnancy. Vitamin B6 (pyridoxine) is also considered a first-line treatment for nausea and vomiting in pregnancy by the American College of Obstetrics and Gynecology (111601). However, it should not be used long-term or without medical supervision and close monitoring. The tolerable upper intake level (UL) refers to vitamin B6 in the form of pyridoxine and is 80 mg daily for those aged 14-18 years and 100 mg daily for 19 years and older (6243).

PREGNANCY: POSSIBLY UNSAFE
when used orally in excessive doses. There is some concern that high-dose maternal vitamin B6 (pyridoxine) can cause neonatal seizures (4609,6397,8197).

LACTATION: LIKELY SAFE
when used orally in doses not exceeding the tolerable upper intake level (UL) of vitamin B6 in the form of pyridoxine 80 mg daily for those aged 14-18 years and 100 mg daily for those 19 years and older. The recommended dietary allowance (RDA) in lactating women is 2 mg daily (6243). There is insufficient reliable information available about the safety of vitamin B6 when used in higher doses in breast-feeding women.

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ANTICONVULSANTS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, glutamine might antagonize the effects of anticonvulsant medications.  Details Glutamine is metabolized to the excitatory neurotransmitter glutamate. Glutamate might have antagonistic effects with anticonvulsant drugs (7292,7293,7294). However, this interaction has not yet been reported in humans.

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AMIODARONE (Cordarone) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, vitamin B6 might increase the photosensitivity caused by amiodarone.  Details Despite initial case reports suggesting that pyridoxine may have a protective effect against amiodarone-induced photosensitivity, preliminary clinical research suggests that pyridoxine may actually exacerbate this adverse effect (8892,8893).

ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, vitamin B6 may have additive effects when used with antihypertensive drugs.  Details Research in hypertensive rats shows that vitamin B6 can decrease systolic blood pressure (30859,82959,83093). Similarly, clinical research in patients with hypertension shows that taking high doses of vitamin B6 may reduce systolic and diastolic blood pressure, possibly by reducing plasma levels of epinephrine and norepinephrine (83091).

LEVODOPA Interaction Rating = Minor Be watchful with this combination. Severity = Moderate •  Occurrence = Unlikely •  Level of Evidence = D Vitamin B6 may increase the metabolism of levodopa when taken alone, but not when taken in conjunction with carbidopa.  Details Vitamin B6 (pyridoxine) enhances the metabolism of levodopa, reducing its clinical effects. However, this interaction does not occur when carbidopa is used concurrently with levodopa (Sinemet). Therefore, it is not likely to be a problem in most people (3046).

PHENOBARBITAL (Luminal) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D High doses of vitamin B6 may reduce the levels and clinical effects of phenobarbital.  Details Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenobarbital, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenobarbital to avoid high doses of vitamin B6 (3046,10801).

PHENYTOIN (Dilantin) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D High doses of vitamin B6 may reduce the levels and clinical effects of phenytoin.  Details Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenytoin, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenytoin to avoid high doses of vitamin B6 (3046,10801).

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General ...Orally and intravenously, glutamine is generally well tolerated.
Most Common Adverse Effects:
Orally: Belching, bloating, constipation, cough, diarrhea, flatulence, gastrointestinal pain, headache, musculoskeletal pain, nausea, and vomiting.

Endocrine ...One case of hot flashes has been reported in a patient taking glutamine 5-15 grams orally twice daily for up to 1 year (96520).

Gastrointestinal ...Orally, glutamine has been associated with belching, bloating, constipation, flatulence, nausea, vomiting, diarrhea, and gastrointestinal (GI) pain. Nausea, vomiting, constipation, diarrhea, and GI pain have been reported in clinical trials using high-dose glutamine 10-30 grams (0.3 grams/kg) in two divided doses daily to treat sickle cell disease (99414). One case of dyspepsia and one case of abdominal pain have been reported in patients taking glutamine 5-15 grams twice daily orally for up to 1 year (96520). In a small trial of healthy males, taking a single dose of about 60 grams (0.9 grams/kg of fat free body mass [FFM]) was associated with a 50% to 79% incidence of GI discomfort, nausea, and belching, compared with a 7% to 28% incidence with a lower dose of about 20 grams (0.3 gram/kg FFM). Flatulence, bloating, lower GI pain, and urge to regurgitate occurred at similar rates regardless of dose, and there were no cases of heartburn, vomiting, or diarrhea/constipation (105013). It is possible that certain GI side effects occur only after multiple doses of glutamine.

Musculoskeletal ...Orally, glutamine 30 grams daily has been associated with cases of musculoskeletal pain and non-cardiac chest pain in clinical trials for patients with sickle cell disease (99414).

Neurologic/CNS ...Orally, glutamine has been associated with dizziness and headache. A single case of dizziness has been reported in a patient treated with oral glutamine 0.5 grams/kg. However, the symptom resolved after reducing the dose to 0.25 grams/kg (91356). Mania and hypomania have been reported in 2 patients with bipolar disorder taking commercially purchased glutamine up to 4 grams daily (7291). Glutamine is metabolized to glutamate and ammonia, both of which might have neurological effects in people with neurological and psychiatric diseases or in people predisposed to hepatic encephalopathy (7293).

Oncologic ...There is some concern that glutamine might be used by rapidly growing tumors and possibly stimulate tumor growth. Although tumors may utilize glutamine and other amino acids, preliminary research shows that glutamine supplementation does not increase tumor growth (5469,7233,7738). In fact, there is preliminary evidence that glutamine might actually reduce tumor growth (5469).

Other ...Orally, glutamine has been associated with cough when a powdered formulation is used. It is unclear if this was due to accidental inhalation. One case of a burning sensation and one case of hypersplenism has been reported in a patient taking glutamine 5-15 grams twice daily orally for up to 1 year (96520).

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General ...Orally or by injection, vitamin B6 is well tolerated in doses less than 100 mg daily.
Most Common Adverse Effects:
Orally or by injection: Abdominal pain, allergic reactions, headache, heartburn, loss of appetite, nausea, somnolence, vomiting.
Serious Adverse Effects (Rare):
Orally or by injection: Sensory neuropathy (high doses).

Dermatologic ...Orally, vitamin B6 (pyridoxine) has been linked to reports of skin and other allergic reactions and photosensitivity (8195,9479,90375). High-dose vitamin B6 (80 mg daily as pyridoxine) and vitamin B12 (20 mcg daily) have been associated with cases of rosacea fulminans characterized by intense erythema with nodules, papules, and pustules. Symptoms may persist for up to 4 months after the supplement is stopped, and may require treatment with systemic corticosteroids and topical therapy (10998).

Gastrointestinal ...Orally or by injection, vitamin B6 (pyridoxine) can cause nausea, vomiting, heartburn, abdominal pain, mild diarrhea, and loss of appetite (8195,9479,16306,83064,83103,107124,107127,107135). In a clinical trial, one patient experienced infectious gastroenteritis that was deemed possibly related to taking vitamin B6 (pyridoxine) orally up to 20 mg/kg daily (90796). One small case-control study has raised concern that long-term dietary vitamin B6 intake in amounts ranging from 3.56-6.59 mg daily can increase the risk of ulcerative colitis (3350).

Hematologic ...Orally or by injection, vitamin B6 (pyridoxine) can cause decreased serum folic acid concentrations (8195,9479). One case of persistent bleeding of unknown origin has been reported in a clinical trial for a patient who used vitamin B6 (pyridoxine) 100 mg twice daily on days 16 to 35 of the menstrual cycle (83103). It is unclear if this effect was due to vitamin B6 intake.

Musculoskeletal ...Orally or by injection, vitamin B6 (pyridoxine) can cause breast soreness or enlargement (8195).

Neurologic/CNS ...Orally or by injection, vitamin B6 (pyridoxine) can cause headache, paresthesia, and somnolence (8195,9479,16306). Vitamin B6 (pyridoxine) can also cause sensory neuropathy, which is related to daily dose and duration of intake. Doses exceeding 1000 mg daily or total doses of 1000 grams or more pose the most risk, although neuropathy can occur with lower daily or total doses as well (8195). The mechanism of the neurotoxicity is unknown, but is thought to occur when the liver's capacity to phosphorylate pyridoxine via the active coenzyme pyridoxal phosphate is exceeded (8204). Some researchers recommend taking vitamin B6 as pyridoxal phosphate to avoid pyridoxine neuropathy, but its safety is unknown (8204). Vitamin B6 (pyridoxine) neuropathy is characterized by numbness and impairment of the sense of position and vibration of the distal limbs, and a gradual progressive sensory ataxia (8196,10439). The syndrome is usually reversible with discontinuation of pyridoxine at the first appearance of neurologic symptoms. Residual symptoms have been reported in patients taking more than 2 grams daily for extended periods (8195,8196). Daily doses of 100 mg or less are unlikely to cause these problems (3094).

Oncologic ...In females, population research has found that a median intake of vitamin B6 1. 63 mg daily is associated with a 3.6-fold increased risk of rectal cancer when compared with a median intake of 1.05 mg daily (83024). A post-hoc subgroup analysis of results from clinical research in adults with a history of recent stroke or ischemic attack suggests that taking folic acid, vitamin B12, and vitamin B6 does not increase cancer risk overall, although it was associated with an increased risk of cancer in patients who also had diabetes (90378). Also, in patients with nasopharyngeal carcinoma, population research has found that consuming at least 8.6 mg daily of supplemental vitamin B6 during treatment was associated with a lower overall survival rate over 5 years, as well as a reduced progression-free survival, when compared with non-users and those with intakes of up to 8.6 mg daily (107134).

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