L-Carnitine 500 mg by GNC Pro Performance

EFFECTIVE

• L-carnitine deficiency. Oral and intravenous L-carnitine can treat primary and secondary L-carnitine deficiency. Details: Administering L-carnitine orally or intravenously is effective for acute or chronic treatment of primary L-carnitine deficiency or secondary L-carnitine deficiency due to inborn errors of metabolism. This is an FDA-approved indication for L-carnitine (4949,58611,59018). For primary or secondary deficiencies, oral L-carnitine 990 mg 2-3 times daily is used. For inborn errors of metabolism resulting in secondary L-carnitine deficiency, L-carnitine 50 mg/kg given as a slow (2-3 minute) bolus injection or by infusion followed by 50 mg/kg administered in divided doses every 3-4 hours over the next 24 hours is also used. Subsequent daily maintenance doses of intravenous L-carnitine are usually around 50 mg/kg (3616).

POSSIBLY EFFECTIVE

• Angina. Oral and intravenous L-carnitine may improve exercise tolerance and symptoms of angina during exercise in patients with angina. Details: Several small clinical trials in patients with chronic stable angina or cardiac syndrome X show that taking L-carnitine orally or intravenously seems to improve exercise tolerance and time to onset of angina when compared with placebo (3623,3624,58156,59096,59118,59216,59217,59230). Oral doses of L-carnitine have ranged from 900 mg to 2 grams daily in single or divided doses for 2 weeks to 6 months (3623,3624,58156,59096,59118,59217). Intravenous L-carnitine 3 grams in 500 mL of 5% dextrose, administered once daily for 14 days (59230), or intravenous DL-carnitine 40 mg/kg administered 30 minutes prior to exercise (59216) have also been used.
• Congestive heart failure (CHF). Oral and intravenous L-carnitine may improve exercise capacity and symptoms of heart failure in patients with CHF. Details: Several small clinical trials in patients with CHF show that taking L-carnitine 1.5-3 grams daily in single or divided doses for up to 34 months or administering intravenous L-carnitine 5 grams daily for 7 days seems to improve symptoms and increase exercise capacity when compared with placebo (3625,3626,58145,58771,58824). Also, taking a specific combination product containing L-carnitine 2250 mg and coenzyme Q10 270 mg (Carni Q-Gel, Tishcon Corporation) daily for 12 weeks appears to improve symptoms of CHF when compared with no treatment (58392).
• Hyperlipidemia. Oral or intravenous L-carnitine may slightly improve lipid levels. Oral, but not intravenous, L-carnitine may also improve lipoprotein(a) levels in patients with elevated lipoprotein(a). Details: Most meta-analyses of clinical research in patients with or without hyperlipidemia show that L-carnitine, given orally at a dose of 76 mg to 3 grams daily or intravenously at a dose of 15-20 mg/kg three times weekly, appears to reduce total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride levels by up to 9.5 mg/dL, 8.3 mg/dL, and 11.2 mg/dL, respectively, while increasing high-density lipoprotein (HDL) cholesterol by up to 1.6 mg/dL. Sub-analyses in patients with elevated levels of specific lipids shows that L-carnitine might be most beneficial in these populations (95073,102019,111886). However, clinical research is generally very low to moderate quality. Also, any effects of L-carnitine on these lipids are modest and might not be considered clinically significant. An umbrella meta-analysis of meta-analyses of clinical research shows that taking L-carnitine orally reduces total cholesterol, LDL cholesterol, and triglyceride levels by only 1.1 mg/dL, 4.8 mg/dL, and 2.5 mg/dL, with increases in HDL cholesterol of 0.7 mg/dL (111896). More information is needed on the effects of L-carnitine on lipid levels specifically in patients with hyperlipidemia. Some research has also evaluated the benefits of L-carnitine in people with hyperlipidemia and elevated lipoprotein(a) levels or those undergoing hemodialysis. Preliminary clinical research and a meta-analysis of clinical research in these populations shows that taking L-carnitine 1-2 grams daily for 8-24 weeks reduces levels of lipoprotein(a) by about 9 mg/dL when compared with control (58155,95073). However, giving L-carnitine intravenously 1 gram three times weekly or 4 grams daily does not improve lipoprotein(a) levels in these patients (95073). Also, oral or intravenous L-carnitine does not improve LDL cholesterol, HDL cholesterol, or triglyceride levels in these patients (58155,95073). Whether L-carnitine reduces the risk of cardiovascular events in patients with hyperlipidemia is unknown.
• Kidney failure. Intravenous, but not oral, L-carnitine is FDA-approved for the prevention and treatment of L-carnitine deficiency in patients with kidney failure undergoing hemodialysis. Any other benefits with the use of L-carnitine in patients on hemodialysis are unclear. Details: Patients with kidney failure undergoing maintenance hemodialysis often experience L-carnitine deficiency, which can lead to lipid, red blood cell, cardiac muscle, and skeletal muscle abnormalities (26496). Use of intravenous L-carnitine for the prevention and treatment of L-carnitine deficiency in people with kidney failure who are undergoing hemodialysis is an FDA-approved indication for L-carnitine. L-carnitine 10-20 mg/kg is given as a slow (2-3 minute) bolus injection, with dose adjustments made based on subsequent pre-dialysis L-carnitine concentrations (3616). However, oral L-carnitine is not FDA-approved for this purpose. There is concern that long-term administration of high doses of oral L-carnitine may result in accumulation of toxic metabolites, including trimethylamine and trimethylamine-N-oxide, in patients with kidney failure (3616). Research in other areas are conflicting. Most clinical research shows that taking L-carnitine 0.7-3 grams or 10 mg/kg daily or administering L-carnitine 2-6 grams or 30-60 mg/kg weekly via intravenous infusion can improve cardiac function, intravenous fistula complications, red blood cell count, hemoglobin, and C-reactive protein levels in patients on hemodialysis (9790,26496,58257,58437,58842,59009,59178,111877). A meta-analysis of 18 clinical studies in adults with kidney-related anemia undergoing hemodialysis shows that receiving oral or intravenous L-carnitine reduces erythropoietin responsiveness and erythropoiesis stimulating agent (ESA) requirement, but not hemoglobin level, when compared with placebo or conventional therapy, regardless of treatment duration or route of administration (107406). Despite an earlier meta-analysis suggesting that L-carnitine does not reduce the incidence of dialysis-related hypotension or muscle cramping (58511), a more recent meta-analysis shows that L-carnitine reduces the incidence of dialysis-related hypotension by 74% when compared with placebo (111878). However, sub-analyses suggest that only oral L-carnitine, and doses of over 4.2 grams weekly for at least 12 weeks, are effective for preventing hypotension (111878). A meta-analysis and some preliminary clinical research also show that muscle cramping is reduced by up to 78% when compared with controls (104176,111878). Additionally, observational research has found that administering at least 1 gram of L-carnitine per dialysis session for at least 10 sessions monthly is associated with a 10% to 20% decrease in the number of hospitalization days during the subsequent month (58409). However, L-carnitine may not be beneficial for improving other measures in people with kidney failure receiving dialysis. While some research shows that L-carnitine decreases lipoprotein(a) levels (44187), low-density lipoprotein (LDL) cholesterol levels (26496,91723,107399), and total cholesterol levels (107399), most research shows that it does not improve serum lipid levels (9790,26496,44187,58257,58320,58842,58939,59009,59025,59031)(59036,59059,59080,90633,91723,107399). Additionally, while one small clinical trial shows that taking L-carnitine can improve performance on some exercise tests (104179), most research shows that L-carnitine does not improve respiratory function or exercise performance. The effect on quality of life is unclear (58154,58437,58472,58743,59031,90633,111867,111877).
• Male infertility. Oral L-carnitine, taken alone or in combination with acetyl-L-carnitine, may increase sperm motility in males with infertility, leading to a greater likelihood of pregnancy in female partners. Details: Although some clinical research has yielded conflicting results (58209,58588,59020,90627,111861), most clinical research shows that taking L-carnitine 1-3 grams daily in divided doses for up to 24 weeks, with or without acetyl-L-carnitine 1 gram daily, increases sperm count and motility, and improves sperm morphology, in males with infertility of various etiologies (12352,58167,58182,58194,58334,58469,58831,58849,59129,59189)(59190,101560,107394,111861,111459,111888,111890). However, it is unclear if taking L-carnitine increases the odds of pregnancy. One meta-analysis of randomized controlled trials shows that taking L-carnitine and acetyl-L-carnitine in combination increases the odds of pregnancy by 3.7-fold over placebo. However most clinical research investigating the effect of L-carnitine alone or with acetyl L-carnitine on pregnancy rates disagrees (12352,58182,101560,111861,111459,111888). The number of studies investigating the effect of L-carnitine alone or with acetyl-L-carnitine on pregnancy rate is small and the duration of supplementation may be inadequate. Taking L-carnitine 1 gram and acetyl-L-carnitine 0.5 grams twice daily after taking nonsteroidal anti-inflammatory drugs for 2 months seems to increase sperm count and motility in males with abacterial prostatovesiculoepididymitis, an inflammation of the prostate gland, seminal vesicles, and epididymis (9791). Some studies have also evaluated L-carnitine in combination with other ingredients. One clinical trial in males with asthenospermia shows that taking L-carnitine 150 mg, acetyl-L-carnitine 50 mg, L-arginine 1660 mg, and Panax ginseng 200 mg daily for 3 months increases sperm motility and sexual satisfaction when compared with no treatment (32189). Another small clinical trial shows that taking this combination along with prulifloxacin 600 mg daily for 6 months improves sperm concentration and motility when compared with prulifloxacin alone in patients with chronic prostatitis due to Chlamydia trachomatis infection (59006). Other small and preliminary clinical studies have investigated the effects of a specific combination product providing L-carnitine 1 gram twice daily for 6 months, along with acetyl-L-carnitine, coenzyme Q10, selenium, zinc, vitamin C, folic acid, vitamin B12, and citric acid (Proxeed Plus). Taking this combination product has been shown to improve measures of sperm quality such as sperm count, sperm concentration, total motility, and progressive motility when compared to baseline. The effect on sperm volume and morphology is unclear. Most research has been conducted in patients with oligoasthenozoospermia, although some benefit has also been shown in patients with varicocele-related infertility, especially those with more severe varicocele (102017,107395,111296). The validity of these findings is limited by the lack of comparator group. Also, it is unclear if these effects are due to L-carnitine, other ingredients, or the combination. The effect of L-carnitine in combination with other ingredients on pregnancy rate has also been examined. One meta-analysis of moderate-quality clinical research shows that taking L-carnitine in combination with micronutrients increases the odds of pregnancy by 3.5-fold over placebo or no treatment (111888).
• Myocarditis. Oral DL-carnitine may prevent myocarditis in children with diphtheria. Details: Myocarditis is a complication of diphtheria. Clinical research in children with diphtheria shows that taking DL-carnitine 100 mg/kg daily for 4 days reduces the risk of myocarditis and mortality when compared with no treatment (3620,3621).
• Valproic acid-induced toxicities. Although more well-designed research is needed to confirm these findings, oral and intravenous L-carnitine may improve neurologic and hepatic function and reduce ammonia levels in patients with these valproic acid-induced toxicities. Details: Valproic acid-induced toxicities are often associated with low plasma and tissue levels of L-carnitine. Preliminary clinical research and case reports in patients on valproic acid therapy who have neurologic or hepatic deterioration or hyperammonemia show that taking L-carnitine 50-100 mg/kg daily in divided doses or administering L-carnitine 150-500 mg/kg daily via intravenous infusion seems to improve neurologic and hepatic function and bring plasma ammonia levels within normal limits (1438,1914,1915,1916,1917,4523,5798,5799,95068). There is also some preliminary evidence that intravenous L-carnitine can prevent the development of severe valproic acid-induced hepatotoxicity when given to patients being treated for overdose and accidental ingestion of valproic acid (1438,4528,5798,5799), especially if treatment is initiated early (4528). Despite these results, most evidence consists of anecdotal individuals or small case series. A more recent retrospective cohort study suggests that treatment with an L-carnitine dosing regimen consisting of a 100 mg/kg intravenous loading dose followed by up to 3 grams daily in divided doses for 3 days or until ICU discharge does not enhance valproic acid elimination or prevent organ dysfunction when compared with patients not treated with L-carnitine (111869). Also, taking L-carnitine does not appear to reduce valproic acid-associated weight gain (58295). Well-designed clinical trials are still needed to determine the role of L-carnitine in the treatment or prevention of valproic acid toxicities.

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Acne. Topical L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One small clinical trial in patients with mild-to-moderate acne shows that applying a proprietary formulation containing L-carnitine, licochalcone, and 1,2-decanediol to the face twice daily for 8 weeks reduces the number of acne lesions and pustules and improves quality of life when compared to baseline. However, the improvements do not appear to be significant when compared with placebo (26493).
• Age-related fatigue. Small clinical studies suggest that oral L-carnitine may improve physical and mental fatigue associated with aging. Details: Two small clinical trials in elderly patients experiencing fatigue after slight physical activity shows that taking L-carnitine 2-4 grams daily for 1-6 months improves physical and mental fatigue, increases muscle mass, and decreases fat mass when compared with placebo (16109,16111).
• Aluminum phosphide poisoning. It is unclear if intravenous L-carnitine is beneficial in people with aluminum phosphide poisoning. Details: A meta-analysis of preliminary clinical research in patients with aluminum phosphide poisoning shows that intravenous L-carnitine does not reduce the odds of mortality when compared with control groups receiving routine treatments only (111892). However, only 2 studies were included in the analysis and both studies may have been underpowered to detect differences.
• Alzheimer disease. Oral L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in patients with mild to moderate Alzheimer disease shows that taking L-carnitine tartrate 3.73 grams, in combination with serine, nicotinamide riboside, and N-acetyl cysteine, daily for 28 days and then twice daily for 56 days does not improve cognitive function when compared with taking placebo. However, in patients with the most severe symptoms, there was some modest improvement (110623). This study may have been underpowered to detect differences. Also, the effect of L-carnitine alone is unclear.
• Androgenic alopecia. It is unclear if topical L-carnitine is beneficial in people with androgenic alopecia. Details: One small clinical trial in individuals with androgenic alopecia shows that applying topical L-carnitine 2% solution to the scalp twice daily for 6 months significantly increases the number of terminal hair shafts on the scalp when compared with placebo (58390).
• Anorexia nervosa. Although there has been interest in using oral L-carnitine for anorexia nervosa, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Anthracycline cardiotoxicity. Oral and intravenous L-carnitine have only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: A small clinical trial in patients with breast cancer undergoing doxorubicin treatment shows that taking a combination of L-carnitine and vitamin E over 4 21-day treatment cycles decreases the proportion of patients with cardiac events by 24.2% when compared with chemotherapy treatment only. There were also modest beneficial effects on some enzyme measures of cardiac health. Patients received L-carnitine 3 grams intravenously on the first day of each cycle followed by an oral intake of 300 mg 4 times daily for the remaining 20 days. Vitamin E 1800 mg daily was taken orally in 3 divided doses (111891).
• Athletic performance. Oral L-carnitine has been evaluated for its effect on athletic performance in several small and short-term clinical studies, with mixed results. Details: Maximal exercise in trained athletes has been associated with a decrease in plasma L-carnitine levels (3648,58583). Theoretically, restoring these levels with L-carnitine supplementation might have beneficial effects. However, clinical studies examining the use of L-carnitine for athletic performance have reported conflicting results. Some clinical studies show that taking L-carnitine 2 grams, either before exercise or daily for up to 6 weeks, enhances athletic performance and endurance and reduces post-exercise muscle pain in male athletes and healthy untrained males (58450,59182,59185), but other studies do not support these findings (1947,59128,59134). Additionally, although some studies show that taking L-carnitine 1-2 grams or 40 mg/kg before exercise or 4 grams daily for 2 weeks can decrease lactate accumulation and increase oxygen uptake, power output, and time to anabolic threshold during exercise (3649,3650,59061,59184,59186), other studies show no improvement in these outcomes (58471,58775,59033,59045,59069,59128). These discrepancies may be related to the small study sizes, short treatment durations, and variable dosing regimens.
• Atrial fibrillation. It is unclear if oral L-carnitine is beneficial for preventing postoperative atrial fibrillation in patients undergoing aortic valve surgery. Details: A very small clinical study in patients undergoing aortic valve replacement or valve-sparing aortic root replacement shows that receiving oral L-carnitine (L-Cartin FF, Otsuka Pharmaceutical) 1 gram three times daily, beginning 2 days prior to surgery and continuing for 7 days after surgery, is associated with a postoperative atrial fibrillation rate of 20%, compared with a rate of 60% in a historical age-matched control group not receiving L-carnitine (107408).
• Attention deficit-hyperactivity disorder (ADHD). It is unclear if oral L-carnitine is beneficial in children with ADHD. Details: One small crossover trial in children with ADHD shows that taking L-carnitine 50 mg/kg twice daily for 6 months improves parent and teacher assessments of behavior when compared with placebo (58166).
• Autism spectrum disorder. Small clinical studies suggest that oral L-carnitine may improve some symptoms of autism spectrum disorder. Details: Small clinical trials in children 3-16 years of age with autism spectrum disorder show that taking L-carnitine 50 mg/kg or 150 mg/kg daily for 8 to 12 weeks modestly improves overall symptoms of autism, especially lethargy, social isolation, hyperactivity, and irritability, when compared with taking placebo. However, there is inconsistency between studies with respect to rating scales used and specific endpoints showing improvement. In one study, children remained on any pre-existing medications; in the other two, all children were also taking risperidone (58981,111887,111900).
• Arrhythmia. Small clinical studies suggest that oral L-carnitine may reduce the incidence of arrhythmias in patients with premature ventricular contractions. Details: Small clinical trials in patients with premature ventricular contractions show that taking L-carnitine 2 grams twice daily for 45 weeks or 2 grams three times daily for 2 weeks might reduce the incidence of arrhythmias when compared to baseline (59043,59120,59143).
• Asthenopia (eye strain). Oral L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research in videoterminal users with computer vision syndrome and without dry eye shows that taking a product containing L-carnitine 50 mg, along with zinc and extracts of elderberry, black currant, and eleuthero root (Meramirt CM) daily for 1 month modestly reduces severity of eye strain and sensitivity when compared with not taking this product (111295). It is unclear if these findings are due to L-carnitine, other ingredients, or the combination.
• Beta-thalassemia. Small clinical studies suggest that oral L-carnitine may improve symptoms and reduce complications of beta-thalassemia minor, intermedia, and major. Details: Several small clinical trials in children with beta-thalassemia major show that taking L-carnitine 50 mg/kg daily for 3-6 months might reduce pulmonary artery systolic pressure, increase cardiac output during exercise, and improve progression to puberty (58294,58502,58556). Clinical research in adults with beta-thalassemia intermedia shows that taking L-carnitine with hydroxyurea appears to increase hemoglobin and hematocrit and reduce left ventricular end-diastolic diameter, a measure of pulmonary hypertension (58679). In patients with beta-thalassemia major or intermedia aged 6 years and up, taking L-carnitine 50 mg/kg daily for 6 months normalized left ventricular dilatation and hypertrophy in 30% and 37% of patients, respectively, compared with only 10% in those taking placebo. Cardiac output was also improved, but there were no changes in blood parameters (101565). Clinical research in children with beta-thalassemia minor shows that taking L-carnitine 50 mg/kg daily, with or without folic acid 1 mg daily, for 3 months appears to reduce bone pain by 84% to 87% and increase the number of climbable stairs 3.1- to 5.2-fold when compared with baseline (90631).
• Cachexia. Small clinical studies suggest that oral L-carnitine may improve body composition and quality of life in patients with cancer-related cachexia. Details: One small clinical trial in patients with cancer-related cachexia shows that taking L-carnitine 4 grams daily for 12 weeks increases body mass index (BMI) when compared with placebo (59029). Other research shows that taking L-carnitine 4 grams daily with megestrol acetate, eicosapentaenoic acid (EPA), and thalidomide for 5 months is more effective than any single product alone for increasing lean body mass in patients with cancer-related cachexia (23437). Additionally, taking L-carnitine 4 grams daily with megestrol acetate, celecoxib, and antioxidants for 4 months appears more effective than megestrol acetate alone for improving lean body mass, fatigue, and quality of life in these patients (59012).
• Cancer-related fatigue. It is unclear if oral L-carnitine is beneficial for improving fatigue in patients with advanced cancer. Details: Some cancer patients have low blood levels of L-carnitine, which may reduce energy production and lead to fatigue. Some small clinical trials in patients with advanced cancer show that taking L-carnitine 3-4 grams daily for 7 days significantly improves some measures of fatigue when compared to baseline (16106,16110). However, other higher quality clinical research shows that taking L-carnitine 2-4 grams daily for 4-12 weeks is no more effective than placebo for improving fatigue in advanced cancer patients (26498,58523,59029).
• Celiac disease. It is unclear if oral L-carnitine is beneficial in patients with celiac disease. Details: Some research shows that L-carnitine blood levels are low in patients with celiac disease. One small clinical trial in patients with celiac disease shows that taking L-carnitine 2 grams daily for 6 months lowers some measures of fatigue when compared with placebo. However, L-carnitine does not significantly improve measures of depression or quality of life in these patients (16105).
• Chemotherapy-related fatigue. It is unclear if oral L-carnitine is beneficial in patients with fatigue due to sunitinib therapy. Details: A small clinical study in adults with renal cell carcinoma who are experiencing fatigue associated with sunitinib treatment shows that taking L-carnitine 1500 mg daily for 2 weeks modestly improves fatigue severity when compared to baseline (100352). The validity of this finding is limited by the small study size and lack of a comparator group.
• Chronic fatigue syndrome (CFS). It is unclear if oral L-carnitine is beneficial in patients with CFS. Details: One small clinical study in adults with CFS shows that taking L-carnitine 1 gram three times daily for 2 months can improve some symptoms of CFS when compared to baseline (3630). The validity of this finding is limited by the lack of a comparator group.
• Chronic obstructive pulmonary disease (COPD). It is unclear if oral L-carnitine is beneficial in patients with COPD. Details: One small clinical study in adults with moderate to severe COPD shows that taking L-carnitine 2 grams daily for 6 weeks improves exercise performance and walking tolerance when compared with placebo (58213).
• Cirrhosis. Preliminary research suggests that oral L-carnitine may be beneficial in patients with cirrhosis. Details: One small clinical trial in patients with cirrhosis who are receiving branched-chain amino acids supplements to improve nutritional status shows that taking L-carnitine 1 gram orally daily for 6 months, in addition to increasing exercise by 2000 steps per day, does not improve muscle volume, handgrip strength, or leg strength, but does reduce complaints of muscle cramping, when compared to baseline (102124). Another small, uncontrolled clinical trial in patients with cirrhosis shows that taking L-carnitine 1800 mg daily for 6 months does not improve Child-Pugh scores, but may improve quality of life, when compared to baseline (104177). The validity of these studies is limited by the lack of comparator groups. The effect of L-carnitine has also been examined retrospectively in patients with cirrhosis. One retrospective study in matched patients that had been admitted to hospital for cirrhosis suggests that taking L-carnitine for more than 30 days is associated with an increase in survival length by about 21 months compared with not taking L-carnitine. Overall, L-carnitine use was also associated with a 36% to 48% increase in the proportion of patients surviving 1-5 years, with the greatest effect in patients with modest to severe liver dysfunction. The median dose of L-carnitine was 1000 mg daily for at least 6 months is associated with a reduced loss of skeletal muscle compared with not taking L-carnitine (111860). The validity of these studies is limited by their retrospective design.
• Cognitive function. It is unclear if oral L-carnitine is beneficial for improving cognitive function in healthy individuals. Details: Low-quality clinical research shows that taking L-carnitine 500 mg as a single dose or 250 mg twice daily for 3 days does not improve cognitive function or memory in otherwise healthy young adults when compared with placebo (58176,95070).
• Coronary heart disease (CHD). It is unclear if oral L-carnitine is beneficial in patients with CHD. Details: One small clinical trial in patients with CHD shows that taking L-carnitine 2 grams prior to exercise does not improve endurance when compared with placebo (58196). Another small clinical trial in patients with CHD shows that taking L-carnitine 1 gram daily for 12 weeks does not improve low-density lipoprotein (LDL) cholesterol, total cholesterol, or apolipoprotein-B when compared with placebo; however, it does appear to increase high-density lipoprotein (HDL) and apolipoprotein A-1 levels in these patients (95071).
• Coronavirus disease 2019 (COVID-19). It is unclear if oral L-carnitine is beneficial for COVID-19 prevention or treatment. Details: Preliminary clinical research in patients hospitalized with mild to moderate COVID-19 shows that taking L-carnitine 1 gram 3 times daily for 5 days does not reduce the incidence of fever or cough when compared with standard treatments only. However, all patients taking L-carnitine survived compared with 86% of those given standard treatment only. Also, there were improvements in oxygen saturation and inflammatory measures (111874). Other clinical research in patients with confirmed asymptomatic or mild COVID-19 shows that taking L-carnitine tartrate (Carnipure) 1 gram 3 times daily for 21 days does not prevent the development of severe lung symptoms when compared with taking placebo. However, in a sub-group of patients, lung lesion improvement was significantly better between days 7 and 14. In adults without COVID-19 but living with someone with confirmed disease, taking this product does not prevent COVID-19 when compared with taking placebo. However, the total number of confirmed illnesses in the population was low (111898).
• Critical illness (trauma). It is unclear if oral or nasogastric L-carnitine is beneficial for critical illness. Details: One small clinical trial in critically ill patients in the ICU shows that receiving L-carnitine (BSK, Zist Takhmir Co, Tehran-Iran) 3 grams daily via a nasogastric tube for 7 days modestly improves disease severity, organ function, inflammatory and other laboratory measures when compared with receiving placebo. Also, mortality rate was reduced by approximately 50%. There was no effect on the duration of hospital or ICU stay (111883,111884). However, another small clinical trial in critically ill patients following an acute ischemic stroke shows that oral or nasogastric L-carnitine tartrate 500 mg every 8 hours for 6 days does not affect the duration of mechanical ventilation or hospital or ICU stay, the severity of illness, or 28-day mortality rates, when compared with taking placebo. There was a modest beneficial effect on insulin resistance (111881). This study was small and may have been underpowered to detect differences.
• Diabetes. Oral L-carnitine may improve glycemic control in patients with diabetes, but it is unclear if these improvements are clinically meaningful. It is also unclear if L-carnitine can improve lipid profiles or weight loss in these patients. Details: While individual study results are mixed (58169,58189,58514,58793,90632,96922,101561), meta-analyses of available clinical research in mixed populations shows that taking L-carnitine 200 mg to 4 grams daily reduces fasting plasma glucose and glycated hemoglobin (HbA1C) levels, and possibly insulin, and improves insulin resistance, when compared with taking placebo or a control diet, although the clinical significance of these improvements is unclear (102018,111875,111886). One meta-analysis shows that these benefits are generally specific to patients with high levels of fasting glucose, diabetes, or obesity, as well as studies investigating L-carnitine in doses of at least 2 grams daily for 12 weeks. However, a small number of studies included in this analysis investigated the effects of acetyl-L-carnitine (111875). Other research in obese patients with type 2 diabetes shows that, when taken with orlistat or sibutramine, L-carnitine 2 grams daily for 12 months decreases body weight and body mass index and improves glycemic control when compared with orlistat or sibutramine alone (58778,58830,58882). The effect of L-carnitine on lipids in people with diabetes is unclear. Some studies show significant reductions in total cholesterol, low-density lipoprotein cholesterol, triglycerides, and/or lipoprotein(a) (58554,58647,58649,90632,101561,107397), while other studies show no improvement in lipid profiles (58169,58189).
• Dilated cardiomyopathy. Small clinical studies suggest that oral L-carnitine may improve ejection fraction in children with dilated cardiomyopathy and adults with ischemic cardiomyopathy. Details: Primary L-carnitine deficiency is a common cause of pediatric dilated cardiomyopathy. Additionally, patients with dilated cardiomyopathy of unknown etiology have been shown to have low cardiac levels of L-carnitine (59196,100351). Due to these findings, L-carnitine has been evaluated for the treatment of dilated cardiomyopathy in children and adults, but the small sizes of these studies and methodological limitations limit the reliability of the results. One small clinical study in children under 13 years of age with dilated cardiomyopathy shows that taking L-carnitine 50-100 mg/kg daily for 1 year in conjunction with standard care improves ejection fraction and reduces left atrial and ventricular diameters when compared with placebo and standard care (100351). The results of this study are limited by the small sample size, unclear etiology of dilated cardiomyopathy, and potential bias. Another small clinical study in children under 5 years of age with dilated cardiomyopathy and low serum levels of L-carnitine shows that taking L-carnitine 100 mg/kg daily for 3 months improves left ventricular ejection fraction (LVEF), cardiac output, and New York Heart Association (NYHA) classification when compared with baseline (59196). Further research is needed to clarify whether L-carnitine is beneficial for most children with dilated cardiomyopathy, or only those with carnitine deficiency. L-carnitine has also been evaluated in older adults. A meta-analysis of clinical studies in mostly older adults with dilated cardiomyopathy shows that addition of intravenous L-carnitine, alone or followed by oral L-carnitine, 1-6 grams daily to conventional therapy for a total of 10-28 days is associated with a 28% increased likelihood of overall efficacy, with improvements observed in both LVEF and cardiac output, when compared with conventional therapy alone (107405). The validity of these findings is limited by the heterogeneity of the included studies, potential publication bias, and unclear reporting. A small individual clinical study in older adults with ischemic cardiomyopathy shows that taking oral L-carnitine daily for 2 months improves LVEF when compared with baseline (58150). The validity of this finding is limited by the lack of a comparator group.
• Dry eye. Topical L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Evidence suggests that chronic use of eye drops containing benzalkonium chloride can cause tear film instability and lead to dry eye (90921). One small clinical trial in patients with glaucoma using eye drops containing benzalkonium chloride shows that using additional eye drops containing L-carnitine (1.017%), eledoisin (0.04%), taurine (0.49%), sodium hyaluronate (0.20 grams/100 mL), and vitamin E acetate (0.20 grams/100 mL) (Carnidrop Plus, Sigma-Tau) three times daily for 15 days reduces dry eye symptoms by approximately 50% when compared to baseline (90625). It is unclear if these findings are due to L-carnitine, other ingredients, or the combination.
• Endometriosis. Although there has been interest in using oral L-carnitine for endometriosis, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Exercise-induced muscle damage. It is unclear if oral L-carnitine tartrate is beneficial for exercise recovery. Details: A small clinical study in healthy males and females participating in moderate physical activity at least 3 days weekly shows that taking a specific product (Carnipure, Lonza Consumer Health, Inc.) providing elemental L-carnitine 2 grams daily for 5 weeks improves perceived recovery and soreness as well as serum creatine kinase levels by 33% and 28%, respectively, when compared with placebo (107398).
• Exercise-induced muscle soreness. Small clinical studies suggest that oral L-carnitine may slightly reduce exercise-induced muscle soreness. Details: Evidence from mostly small clinical trials, when considered alone or combined via meta-analysis, shows that taking L-carnitine 1-3 grams daily for around 3 weeks modestly reduces exercise-induced muscle soreness, especially in the period of 24-48 hours after exercise. Benefits may last up to 96 hours post-exercise. Levels of creatinine kinase, lactate dehydrogenase, and myoglobin also appear to improve with L-carnitine supplementation, reflecting a reduction in muscle damage (58326,58709,59148,101567).
• Hepatic encephalopathy. Oral or intravenous L-carnitine may improve biochemical markers of disease severity in patients with hepatic encephalopathy, but L-carnitine does not seem to improve clinically important outcomes such as fatigue, quality of life, or overall disease severity. Details: A meta-analysis of nine studies in adults with hepatic encephalopathy shows that taking L-carnitine 1-6 grams daily orally or intravenously for up to 90 days increases albumin levels and decreases plasma levels of ammonia, bilirubin, aspartate aminotransferase (AST), blood urea nitrogen (BUN), and creatinine, but does not improve fatigue or quality of life, when compared with placebo (102122). A more recent clinical trial shows that taking L-carnitine 2 grams daily for 24 weeks modestly improves bilirubin levels and some measures of cognitive and liver health, but not quality of life, when compared with taking placebo (111876). Two of the clinical trials included in this analysis also show that taking L-carnitine 2 grams daily for 60-90 days significantly improves cognitive function when compared with placebo in adults with hepatic encephalopathy (58174,58204). Another small clinical trial in patients with advanced liver cirrhosis shows that L-carnitine improves psychometric response to the ammonia tolerance test, suggesting that L-carnitine might be useful in the prevention of hepatic encephalopathy (58872). L-carnitine has also been evaluated in combination with rifaximin. A small clinical study in patients with overt hepatic encephalopathy shows that taking oral L-carnitine 1500 mg in combination with rifaximin 1200 mg three times daily for 12 weeks has no effect on the modified portal systemic encephalopathy index when compared with rifaximin alone. L-carnitine improved blood ammonia levels at 4 weeks, but not at 8 or 12 weeks (107410).
• Hepatitis-related fatigue. It is unclear if oral L-carnitine is beneficial in patients with hepatitis-related fatigue. Details: One small clinical trial in patients with hepatitis C who are receiving interferon-alpha treatment shows that taking L-carnitine 2 grams daily significantly reduces fatigue when compared with interferon-alpha alone. L-carnitine appears to reduce fatigue within the first 3 months of treatment, but not after 6 months (16104).
• Hepatitis B. Oral L-carnitine has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research in patients with hepatitis B shows that taking a specific vitamin complex providing L-carnitine 2472 mg (Godex, Celltrion Pharm) in combination with entecavir 0.5 grams daily for 12 months normalizes alanine transaminase (ALT) levels in 95% and 100% of patients after 3 months and 12 months, respectively, compared to 59% and 86% of patients taking entecavir alone. However, the L-carnitine complex does not appear to improve aspartate transaminase (AST) levels or reduce hepatitis B virus titers (91724). It is unclear if these findings are due to L-carnitine, other ingredients, or the combination.
• Hepatitis C. Small clinical studies suggest that oral L-carnitine may improve response to treatment and markers of liver function in patients with hepatitis C. Details: Two small clinical trials in patients with chronic hepatitis C show that taking L-carnitine 2 grams once or twice daily along with interferon-alpha and ribavirin for 12 months modestly improves response to treatment, increases hemoglobin and red blood cell counts, reduces aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, and reduces steatosis when compared with interferon-alpha and ribavirin treatment alone (58405,59010).
• HIV/AIDS. Although there has been interest in using intravenous L-carnitine to increase CD4 counts in patients with HIV/AIDS, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Hyperthyroidism. It is unclear if oral L-carnitine is beneficial in patients with hyperthyroidism. Details: One small clinical trial in females with hyperthyroidism shows that taking L-carnitine 2-4 grams daily for 2-6 months seems to significantly improve symptoms associated with hyperthyroidism, such as palpitations, nervousness, tremors, and asthenia, when compared with placebo (8047).
• Hypertriglyceridemia. It is unclear if oral L-carnitine is beneficial in patients with hypertriglyceridemia. Details: Small clinical studies in patients with hypertriglyceridemia show that taking L-carnitine 1 gram daily for 12 weeks does not reduce triglyceride levels when compared with placebo (59028,59244).
• Hypothyroidism. It is unclear if oral L-carnitine is beneficial for improving fatigue in patients with hypothyroidism. Details: One small clinical trial in patients with secondary hypothyroidism shows that taking L-carnitine (Ildong Pharmaceutical Co.) 990 mg twice daily for 12 weeks in addition to adequate doses of levothyroxine does not reduce overall fatigue severity when compared with placebo. However, taking L-carnitine might improve physical and mental fatigue in patients with secondary hypothyroidism that are less than 50 years of age. L-carnitine might also improve mental fatigue in patients that underwent thyroidectomy for thyroid cancer (95069).
• Infertility. It is unclear if oral L-carnitine is beneficial for female infertility. Details: One uncontrolled clinical trial in females who had failed to conceive in previous in vitro fertilization (IVF) cycles shows that taking L-carnitine (L-CAR Basic Premium; AA Project Co. ltd.) 1000 mg daily for an average of 82 days does not improve the number of retrieved oocytes or fertilization rates when compared with previous IVF cycles. However, embryo quality at days 3 and 5 of insemination was improved, resulting in an increase in the rate of transferable embryos from 60% in previous cycles to 67%, morphologically good-quality embryos from around 46% to 54%, and blastocysts from around 11% to 21%. The most evidence of benefit was seen in those taking L-carnitine for the shortest time length of 7-44 days (96933).
• Intermittent claudication. Although there has been interest in using oral L-carnitine for intermittent claudication, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Liver disease. Small clinical studies suggest that oral L-carnitine may modestly improve some, but not all, lipid parameters in adults with liver disease. Details: A meta-analysis of six small, low-quality clinical trials in patients with hepatitis C, nonalcoholic steatohepatitis (NASH), and nonalcoholic fatty liver disease (NAFLD) shows that taking L-carnitine moderately reduces total cholesterol and slightly reduces triglyceride levels, but does not improve low-density lipoprotein (LDL) cholesterol or high-density lipoprotein (HDL) cholesterol levels, when compared with control. Studies evaluating L-carnitine doses of 2 grams daily or less and study durations of 24 months or longer showed the largest effect on lipid levels (104178). Another meta-analysis of preliminary clinical research in patients with hepatitis B or C, hepatic encephalopathy, NASH, or NAFLD shows that taking L-carnitine modestly reduces levels if aspartate aminotransferase (AST) and alanine aminotransferase (AST) when compared with taking placebo or no L-carnitine. Some of the studies included in this analysis used acetyl-L-carnitine. However, a meta-analysis of two studies investigating the effect of carnitine orotate shows that taking this compound increases the proportion of patients with normal ALT levels by 4.6 fold (111871).
• Liver transplant. It is unclear if oral L-carnitine is beneficial in patients awaiting a liver transplant. Details: One small clinical trial shows that taking L-carnitine 500 mg three times daily while awaiting a liver transplant does not reduce the incidence of primary graft dysfunction (PGD) or non-function (PNF) when compared with placebo. However, survival one month after surgery was 97% in those taking L-carnitine, compared with 74% in those taking placebo (101562). This study may have been inadequately powered to detect a difference in the incidences of PGD and PNF between groups.
• Low birth weight. It is unclear if oral or intravenous L-carnitine is effective for increasing body weight in preterm infants. Several small clinical studies show conflicting results. Details: Several very small clinical trials in preterm infants receiving total parenteral nutrition show that administering L-carnitine orally at a dose of 13-60 mcmol/kg or intravenously at a dose of 10 mg/kg or 50-100 mcmol/kg daily can improve fat utilization and weight gain when compared with control (3633,3634,3635,3636,3637,58902,59097). However, other small clinical studies show that supplementation with L-carnitine does not significantly increase body weight in preterm infants (58190,58800,59161). The reasons for the discrepant findings are unclear, but due to small study size, some of the studies may have been underpowered to detect significant differences between groups.
• Lyme disease. Although there has been interest in using oral L-carnitine for Lyme disease, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Metabolic syndrome. It is unclear if oral or intravenous L-carnitine is beneficial in patients with metabolic syndrome. Details: One very small clinical trial in patients with metabolic syndrome undergoing 2 days of moderate calorie restriction followed by a 5-day modified fasting period shows that intravenous L-carnitine 2 grams twice daily for 7 days increases weight loss by 1.4 kg and decreases waist circumference by 3.3 cm when compared with intravenous saline. Perceived hunger scores, physical fatigue, and insulin levels were also improved. However, there were no effects on blood pressure (90634). Other clinical research in patients with metabolic syndrome and a total carotid plaque volume of at least 50 mm³ shows that taking L-carnitine 2 grams daily for 6 months does not affect the progression of carotid plaque volume when compared with taking placebo. Also, taking L-carnitine increased the progression of carotid plaque stenosis by 9.3%, as well as levels of low-density lipoprotein (LDL) cholesterol, in this population (111879).
• Migraine headache. It is unclear if oral L-carnitine is beneficial in patients with migraine headaches. Details: One small clinical trial in patients with migraines shows that taking L-carnitine 500 mg daily, with or without magnesium oxide, for 12 weeks does not significantly reduce migraine frequency or severity when compared with a control (59030). However, another small preliminary clinical trial in children with episodic migraines shows that taking L-carnitine 25 mg per kg twice daily for 12 weeks prophylactically is as effective as taking propranolol 1 mg/kg once daily for reducing the frequency, severity, and duration of migraine headaches (111870). These studies were small and may have been underpowered to detect differences between groups.
• Muscle cramps. It is unclear if oral L-carnitine is beneficial in patients with muscle cramps. Details: One small, uncontrolled clinical trial in adults with type 2 diabetes shows that taking L-carnitine 300 mg twice daily for 4 months decreases the monthly frequency of muscle cramps from around 4 cramps per month at baseline to around 1 cramp per month after treatment. When compared with baseline, pain was also reduced by about 1 point on a 5-point scale (96922). However, the lack of a placebo control group limits the validity of these findings.
• Multiple sclerosis-related fatigue. It is unclear if oral L-carnitine is beneficial in patients with multiple sclerosis-related fatigue. Details: Some patients with multiple sclerosis have low blood levels of L-carnitine. Additionally, immunosuppressive therapy for multiple sclerosis can cause fatigue. One small, open-label clinical trial in patients with multiple sclerosis receiving immunosuppressive therapy and with low L-carnitine levels shows that taking L-carnitine 3-6 grams daily decreases some measures of fatigue when compared with no treatment (16107).
• Myocardial infarction (MI). It is unclear if oral or intravenous L-carnitine is beneficial in patients who have experienced an MI. Details: Some clinical research shows that taking L-carnitine orally or intravenously after MI reduces premature ventricular beats (58172,59044), improves myocardial viability (59248) and left ventricular function (3628), and reduces mortality (3627,3629,59037). However, other studies show no change in left ventricular functioning (58148) or mortality after taking L-carnitine (3628,58225,90630). The reasons for these discrepant findings are unclear, but may be due to differences in the dosing regimens and length of follow-up. Oral L-carnitine doses have ranged from 2-4 grams daily for up to 12 months (3627,3629,59248). Intravenous L-carnitine has been dosed at 5 grams within the first 36 hours after an MI followed by 3 grams twice daily on days 3-7 (58172), 100 mg/kg every 12 hours for 36 hours (59044), or 9 grams daily for 5 days followed by oral L-carnitine 6 grams daily for 12 months (3628).
• Narcolepsy. It is unclear if oral L-carnitine is beneficial in patients with narcolepsy. Details: One small clinical trial in patients with narcolepsy shows that taking L-carnitine 340 mg in the morning and 170 mg in the evening for 8 weeks reduces dozing off time during the day by about 9 minutes when compared with placebo. However, the number of naps needed, quality of life, and sleepiness are not affected (90624).
• Neonatal apnea. It is unclear if intravenous L-carnitine is beneficial for preventing neonatal apnea in premature infants. Details: One small clinical trial in premature infants shows that adding L-carnitine 30 mg/kg daily to total parenteral nutrition or oral feeds does not affect ventilator requirements or reduce the incidence of apnea when compared with placebo (58163).
• Nonalcoholic fatty liver disease (NAFLD). It is unclear if oral L-carnitine is beneficial in children and adults with NAFLD. Details: One small clinical study in adults with NAFLD shows that taking L-carnitine 600 mg daily for 3 months improves markers of liver function when compared with baseline. No improvements in liver function markers were reported in patients in the control group; however, no statistical comparisons were conducted between groups (58808). A small clinical study in children aged 5-15 years with NAFLD receiving vitamin E shows that taking L-carnitine 25 mg/kg twice daily (maximum of 500 mg twice daily) for 3 months has no effect on aminotransferase concentrations or sonographic grades of fatty liver when compared with placebo (107401).
• Nonalcoholic steatohepatitis (NASH). It is unclear if oral L-carnitine is beneficial in patients with NASH. Details: One small clinical trial in patients with NASH shows that taking L-carnitine 1 gram after breakfast and 1 gram after dinner daily along with following a specific diet improves markers of liver function when compared with diet alone (58715). Another small clinical trial in patients with obesity and nonalcoholic steatohepatitis taking simvastatin 20 mg daily and following a hypocaloric diet shows that taking L-carnitine 10 mL twice daily for 90 days modestly reduces BMI, and improves liver health, lipid, and glycemic indices, when compared with taking a product described as essential phospholipids (111893).
• Obesity. Oral L-carnitine seems to have a small effect on weight loss in overweight or obese individuals when taken for up to 6 months, but some conflicting results exist. Doses of 2 grams daily seem to offer the most benefit. Details: Meta-analyses of clinical trials show that taking L-carnitine 250 mg to 4 grams daily reduces weight and body mass index (BMI) by a small amount when compared with a control group not taking L-carnitine (95074,101563,101564). Subgroup analyses show that L-carnitine only reduces BMI and weight in overweight or obese patients. Taking L-carnitine did not affect weight or BMI in patients with a BMI of up to 25 kg/m2 or in patients undergoing hemodialysis (101563,101564). Another subgroup analysis shows that the largest benefit occurs at a dose of 2 grams daily (101564). In patients with obesity and nonalcoholic steatohepatitis taking simvastatin 20 mg daily and following a hypocaloric diet, one clinical trial shows that taking L-carnitine 10 mL twice daily for 90 days modestly reduces BMI, and improves liver health, lipid, and glycemic indices, when compared with taking a product described as essential phospholipids (111893). However, conflicting results exist. One subgroup analysis in overweight or obese individuals shows that there is no effect on BMI when L-carnitine is taken for 24 weeks or more (101563). One meta-analysis of two small clinical trials in patients with overweight or obesity shows that taking L-carnitine is no more effective than lifestyle modification for reducing body weight (111866). Also, some clinical research shows that taking L-carnitine does not reduce body weight in obese females. Doses used in these studies include L-carnitine 1 gram daily for 12 weeks or 2 grams twice daily for 8 weeks along with exercise (58151,111872). The effect of L-carnitine on cardiovascular risk has also been examined in patients with obesity. One small clinical trial shows that taking L-carnitine 1 gram daily for 12 weeks modestly reduces the lipid accumulation index, based on waist circumference and blood triglyceride levels, when compared with taking placebo. However, there was no effect on other cardiovascular risk indices based on ratios of triglycerides, high-density lipoprotein (HDL) cholesterol, and/or low-density lipoprotein (LDL) cholesterol levels (111872). L-carnitine has also been evaluated in combination with weight loss medications. Clinical research shows that taking L-carnitine 2 grams daily along with orlistat 360 mg daily or sibutramine 10 mg daily for 1 year decreases body weight and BMI when compared with orlistat or sibutramine alone in obese adults with type 2 diabetes (58778,58830,58882).
• Osteoarthritis. It is unclear if oral L-carnitine is beneficial in patients with knee osteoarthritis. Details: A small clinical study in females with knee osteoarthritis and overweight or obesity who are on a low-calorie diet shows that taking L-carnitine 1 gram daily for 12 weeks does not improve pain, stiffness, or physical function when compared with placebo (107403).
• Pemphigus. Although there has been interest in using oral L-carnitine for glucocorticoid-induced muscle wasting in patients with pemphigus, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Peripheral arterial disease (PAD). It is unclear if oral L-carnitine is beneficial in patients with PAD. Details: One small clinical trial in patients with PAD shows that taking L-carnitine 2 grams twice daily for 3 weeks may improve walking distances in people with PAD (3631). However, another small clinical trial in patients with PAD or coronary heart disease shows that taking L-carnitine 2 grams two hours before exercise does not improve endurance (58196). Also, adding L-carnitine 1 gram twice daily to cilostazol therapy for 180 days does not appear to confer additional benefit in this patient population (59023).
• Polycystic ovary syndrome (PCOS). It is unclear if oral L-carnitine is beneficial for improving pregnancy rates or cardiovascular risk in people with PCOS. The effect of L-carnitine on body composition has promising results. Details: Clinical research shows that adding L-carnitine 3 grams daily for 3 months to standard clomiphene plus metformin therapy improves menstrual regularity by 20%, ovulation rate by 24%, and pregnancy rate by 21% when compared with placebo (102123). Preliminary clinical research in patients with PCOS who are resistant to both clomiphene and human chorionic gonadotropin (HCG) shows that taking L-carnitine 2 grams twice daily from day 3 of clomiphene treatment until HCG injection results in the presence of a dominant follicle in 64% of cycles and pregnancy in 20% of cycles (96936). However, L-carnitine may not be beneficial in combination with assisted reproductive technology (ART), including in vitro fertilization and intracytoplasmic sperm injection. A small clinical study in patients with PCOS receiving ART in combination with a gonadotropin-releasing hormone antagonist protocol shows that adding L-carnitine 3000 mg daily during the induction of ovulation (from the second day of the cycle until the day of oocyte triggering) does not improve pregnancy rates in frozen-thawed embryo transfer cycles when compared with control (107409). The effect of L-carnitine has also been examined on anthropometric and cardiovascular risk indices in patients with PCOS. One small clinical study shows that taking L-carnitine 250 mg daily for 12 weeks reduces body weight by 2.8 kg, body mass index (BMI) by 1.2 kg/m2, waist circumference by 1.7 cm, and hip circumference by 2.2 cm when compared with placebo (96935). A meta-analysis of this and other small studies also shows that L-carnitine modestly reduces BMI when compared with placebo in patients with PCOS (111873). Although several studies also show improvements in markers of glycemic control and insulin sensitivity, most research does not support beneficial effects on lipid levels, cardiovascular risk, or liver fat content (96935,107402,107404).
• Rett syndrome. It is unclear if oral L-carnitine is beneficial in patients with Rett syndrome. Details: Two small clinical studies in children with Rett syndrome show that taking L-carnitine 100 mg/kg daily in two or three divided doses for up to 6 months modestly improves well-being, motor skills, sleep efficiency, and communication skills when compared with control or placebo (1433,58161).
• Sarcopenia. Oral L-carnitine may be beneficial for preventing sarcopenia in adults over 75 years of age, but not in healthy older females. Details: One small clinical trial in healthy, active, older females aged 65-70 years shows that taking L-carnitine, as L-carnitine-l-tartrate 1500 mg, daily for 24 weeks does not improve muscle strength or muscle mass when compared with placebo (96930). An additional preliminary clinical trial in females aged 60-75 years taking part in a twice weekly resistance exercise program shows that taking L-carnitine tartrate 1 gram daily with L-leucine 3 grams daily for 24 weeks does not improve muscle strength or volume when compared with taking L-leucine 4 grams daily or no supplementation (111880). These studies were small and may have been underpowered to detect differences. In contrast, in weaker adults 75 years of age and older, taking L-carnitine 2-4 grams daily for 1-6 months increases muscle mass by approximately 2-4 kg when compared with placebo (16109,16111).
• Sepsis. Small clinical studies suggest that intravenous L-carnitine may not reduce mortality in patients with sepsis, although patients with more severe sepsis may see some benefit. Details: Meta-analyses of generally low-quality small clinical trials in patients with sepsis shows that intravenous administration of L-carnitine, 2-6 grams as a bolus followed by a 4-12 gram infusion, does not reduce the risk of 28-day or 1-year mortality when compared with placebo (104180,111868). However, in a subgroup analysis of patients with more severe sepsis, classified as those with a sequential organ failure assessment score (SOFA) of greater than 12, the risk of 1-year mortality was reduced by 32% when compared with placebo (104180).
• Spinal muscular atrophy. Although there has been interest in using oral L-carnitine for spinal muscular atrophy, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Theophylline-induced cardiac toxicity. It is unclear if intravenous L-carnitine is beneficial in patients with theophylline-induced cardiac toxicity. Details: One small clinical trial shows that intravenous administration of L-carnitine 100 mg/kg over 30-60 minutes followed by 50 mg/kg every 8 hours along with intravenous propranolol within 24 hours of theophylline intoxication improves symptoms associated with theophylline-induced cardiac toxicity when given along with standard treatment. This combination led to greater improvements than either agent used alone. These included improvements in serum theophylline levels, heart rate, arrhythmia, mean arterial pressure, and duration of hospital stay. When L-carnitine was used without propranolol, only respiratory rate and theophylline levels over 24 hours were improved to a greater extent than with standard treatment alone (101566).
• Toxin-induced liver damage. Small clinical studies have evaluated oral and intravenous L-carnitine for the management of liver damage caused by different classes of drugs, including antimycobacterial antibiotics and asparaginase-based agents, with promising results. Details: The antimycobacterial antibiotics used to treat tuberculosis, including isoniazid, rifampicin, and pyrazinamide, have been associated with hepatotoxicity (90922). Clinical research shows that taking L-carnitine 2 grams in two divided doses daily for 4 weeks along with a standard treatment regimen for tuberculosis reduces the percentage of treatment-naïve patients with drug-induced hepatotoxicity by almost half when compared with placebo (26499). The asparaginase-based medications have also been associated with hepatotoxicity. Two case series of children with hyperbilirubinemia caused by treatment with L-asparaginase or pegaspargase show that administering intravenous L-carnitine 50-100 mg/kg daily improves bilirubin levels (100353,100354). One case series also suggests that taking oral L-carnitine 50-100 mg/kg daily can help to prevent hyperbilirubinemia in patients with a history of asparaginase-induced hepatotoxicity (100353).
• Traumatic brain injury (TBI). Although there has been interest in using oral L-carnitine for TBI, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose.
• Urinary tract infections (UTIs). It is unclear if oral L-carnitine is beneficial in children with UTIs. Details: One small clinical trial in children 6 months to 10 years of age shows that taking L-carnitine 50 mg/kg daily as a syrup along with antibiotics for 7 days prevents renal scarring associated with acute pyelonephritis. Kidney damage was resolved in 50% of children taking L-carnitine, compared with 13% of children taking placebo. There were no differences in urine cultures between groups (101568).
• Venous leg ulcers. Although there has been interest in using oral L-carnitine for venous leg ulcers, there is insufficient reliable information about the clinical effects of L-carnitine for this purpose. More evidence is needed to rate L-carnitine for these uses.

(Read more about L-CARNITINE)

LIKELY SAFE ...when used orally and appropriately. L-carnitine has been safely used in clinical trials lasting up to 12 months (1947,3620,3621,3623,3624,3625,3626,3627,3628,3629) (3630,3639,4949,8047,9790,12352,16104,16105,16106,16107) (16109,16110,23437,26496,26499,58150,58156,58161,58169,58182) (58189,58204,58207,58209,58213,58294,58523,58554,58556,58647) (58679,58715,58778,58793,58830,58831,58882,59023,59029,59043) (90624,90633,104177,111872,111876,111883,111884,111891,111898). ...when used parenterally as an FDA-approved prescription medicine. Avoid using D-carnitine and DL-carnitine. These forms of carnitine can act as competitive inhibitors of L-carnitine and may cause symptoms of L-carnitine deficiency (1946).

CHILDREN: POSSIBLY SAFE
when used orally or intravenously and appropriately. L-carnitine has been safely used orally in children for up to 6 months (1433,3622,58166,58502,58981,59188,111887,111900). It has also been safely used orally and intravenously in preterm infants (3633,3634,3635,3636,3637,58163,58190,58800,58902,59097)(59161).

PREGNANCY:
Insufficient reliable information available; avoid using.

LACTATION: POSSIBLY SAFE
when used orally. Supplemental doses of L-carnitine have been given to infants in breast milk and formula with no reported adverse effects. The effects of large doses used while nursing are unknown, but L-carnitine is secreted in the breast milk (3616).

(Read more about L-CARNITINE)

ACENOCOUMAROL (Sintrom) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, L-carnitine might increase the anticoagulant effects of acenocoumarol.  Details L-carnitine might enhance the anticoagulant effects of acenocoumarol, an oral anticoagulant similar to warfarin, but shorter-acting (9878,12165). There are at least two case reports of INR elevation with concomitant use. In one case, a 33-year-old male with a previously stable INR had an elevated INR of 4.65 after L-carnitine was started and continued for 10 weeks. INR normalized after discontinuation of the L-carnitine-containing product (12165).

THYROID HORMONE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Theoretically, L-carnitine might decrease the effectiveness of thyroid hormone replacement.  Details L-carnitine appears to act as a peripheral thyroid hormone antagonist by inhibiting entry of thyroid hormone into the nucleus of cells (12761). Taking L-carnitine also seems to diminish some of the symptoms of hyperthyroidism (8047).

WARFARIN (Coumadin) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, L-carnitine might increase the anticoagulant effects of warfarin.  Details L-carnitine might increase the anticoagulant effects of acenocoumarol, a shorter-acting oral anticoagulant similar to warfarin (9878,12165). There is not enough information to know whether this interaction occurs with L-carnitine and warfarin.

(Read more about L-CARNITINE)

General ...Orally and intravenously, L-carnitine is generally well tolerated.
Most Common Adverse Effects:
All routes of administration: Abdominal cramps, abdominal pain, diarrhea, gastritis, heartburn, nausea, reduced appetite, and vomiting. A fish-like body odor has also been reported.
Serious Adverse Effects (Rare):
All routes of administration: Seizures.

Cardiovascular ...According to population research, plasma L-carnitine levels are associated with increased risk of cardiovascular disease and major cardiac events (90635). However, oral supplementation with L-carnitine does not appear to be associated with an increased risk of cardiovascular disease. In fact, a meta-analysis of clinical research shows that L-carnitine supplementation is associated with a reduction in all-cause mortality, as well as ventricular arrhythmias and the development of angina and does not increase the development of heart failure or myocardial reinfarction (59037). Also, another meta-analysis suggests that L-carnitine does not affect mortality or cardiovascular outcomes in patients with a previous myocardial infarction (90630).

Dermatologic ...Orally, L-carnitine has been reported to cause skin rash in a small number of cases (16105,91724). Two patients in a hair growth study using topical carnitine reported mild itching and increased dandruff, while a third reported strong itching with reddish bumps and a burning sensation (58390). When a specific formulation containing L-carnitine, licochalcone, and 1,2-decanediol was applied to the face, mild skin dryness and tightness was reported by 12% of volunteers, compared with 4% to 8% of those in the vehicle-only control group (26493).

Gastrointestinal ...Orally and intravenously, L-carnitine has been associated with nausea, epigastric discomfort, vomiting, abdominal cramps, heartburn, gastritis, anorexia, and diarrhea (3616,3624,59030,95069,95070,101562,107410,111870,111887,111891). Orally, diarrhea or colitis symptoms (1433,3630,16105,16107,16111,23437,58523,58554,59020,90623), nausea and abdominal pain (16105,16106,26499,58169,58392,58554,90623,90634), indigestion (26703), and constipation (58523) have been reported in various clinical trials.

Hematologic ...In one case report, L-carnitine 990 mg twice daily was started in a female presenting to hospital with valproic acid toxicity. Blood phosphorous levels subsequently fell from 2.3 mg/dL to 1.3 mg/dL over 4 days. After discontinuation of L-carnitine, blood phosphorus levels increased to 1.8 mg/dL. The authors suggested that the role of L-carnitine in improved protein metabolism may play a role in the declining levels of phosphorous in the blood and increased risk of hypophosphatemia (90628).

Neurologic/CNS ...Orally or intravenously, L-carnitine has been associated with seizures (3616). Orally, use of L-carnitine in clinical trials has resulted in headache, although this event is rare (58554,95070,111891). L-carnitine may also cause agitation (95070).

Other ...Orally or intravenously, L-carnitine has been associated with a fish-like body odor (1433,3616,58166,59854,90623). One of its metabolites, trimethylamine N-oxide, can cause the urine, breath, and sweat to have a fishy odor (12756,58664).

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