Standardized Guarana by GNC Herbal Plus

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Anxiety. Oral guarana has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Preliminary clinical research shows that taking two tablets of a specific product (Euphytose) containing hawthorn, black horehound, passionflower, valerian, cola nut, and guarana three times daily for 28 days can reduce the severity of anxiety in a greater percentage of patients with adjustment disorder with anxious mood compared to placebo (6250). However, because guarana was included in the supplement as a mild stimulant, it is unclear if this component contributed to the antianxiety effect of the product.
• Athletic performance. Oral guarana has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: Clinical research shows that taking a single dose of a specific product (Berocca Boost, Bayer) containing guarana 222.2 mg (standardized to 40 mg caffeine), B vitamins, vitamin C, and minerals slightly improves exercise tolerance in trained individuals by approximately 2% when compared with placebo (91491). A small crossover study in young adult recreational handball players shows that taking a specific multi-ingredient supplement product (Olimp, Poland) containing guarana, caffeine, and other ingredients (total caffeine content 300 mg) prior to exercise slightly improves the time to complete agility testing but does not increase jump height when compared with placebo. However, taking a supplement containing only guarana and caffeine (total caffeine content 300 mg) does not improve agility or jump height (111577). It is unclear if the effects in these studies are due to guarana, other ingredients, or the combination.
• Cancer-related anorexia. It is unclear if oral guarana is beneficial for anorexia in patients with cancer. Details: A preliminary clinical study shows that taking guarana extract might improve appetite and reduce weight loss in some patients with cancer-related anorexia. Taking guarana extract (Pharmanostra) 50 mg twice daily for 4 weeks stabilized or increased weight in 55% of patients and stabilized or improved appetite in 89% of patients. However, only two patients achieved a weight gain of at least 5%, which was the minimum weight gain considered to be a positive response (91487).
• Cancer-related fatigue. It is unclear if oral guarana is beneficial for fatigue in patients with cancer. Details: Meta-analyses of small clinical studies in patients with solid tumors or breast cancer who are receiving chemotherapy or radiation therapy show that taking guarana 75-100 mg daily for 2-12 weeks does not improve cancer-related fatigue when compared with placebo (108016,111576). Additionally, a systematic review of clinical studies in patients with a variety of solid tumor types found no difference in cancer-related fatigue following at least 5 weeks of guarana consumption (108016). Most studies included in the meta-analysis and systematic review were low-quality, and all studies were conducted in Brazil. Higher quality studies in other geographic locations are needed to confirm these findings.
• Chemotherapy-related fatigue. It is unclear if oral guarana is beneficial for fatigue in patients receiving chemotherapy. Details: In patients with breast cancer, clinical research shows taking guarana extract 50 mg twice daily for 21 days improves fatigue in 52% to 66% of patients, compared with only 10% to 13% in the placebo group (91482). Other preliminary clinical research shows that taking guarana extract 37.5 mg twice daily for 3 weeks improves or stabilizes fatigue in 90% of patients with chemotherapy-related fatigue when compared with baseline. However, when compared with placebo for an additional 3 weeks, guarana does not affect fatigue (91483). Other clinical research shows that taking a dried, purified extract of guarana (PC-18) in doses of 7.5, 12.5, or 37.5 mg twice daily for 21 days improves fatigue in patients with breast cancer when compared with baseline, but not when compared with placebo. It is possible that the magnesium silicate used as a filler in both active and placebo treatments in this study contributed a fatigue-reducing effect (99049).
• Chronic fatigue syndrome (CFS). Although there has been interest in using oral guarana for CFS, there is insufficient reliable information about the clinical effects of guarana for this condition.
• Cognitive function. It is unclear if oral guarana is beneficial for improving cognitive function. Details: In healthy individuals, some clinical research shows that taking a single dose of guarana dry extract 37.5-75 mg, containing 11% to 12% caffeine, improves the speed of cognitive task performance and memory for up to 6 hours, but does not improve reaction time or speed and accuracy of memory, when compared with placebo. Higher doses of guarana 150-300 mg do not appear to be effective (54374,91484). However, a small clinical study in young adult cyclists shows that taking guarana powder 125 mg/kg 30 minutes prior to cognitive testing improves reaction time and alertness scores when compared with placebo, but not when compared with caffeine (111361). Other clinical research shows that taking guarana powder 500 mg, containing 2.1% to 2.5% caffeine, twice daily for 3-150 days does not improve cognitive function when compared with placebo in adults or elderly individuals (54402,54414). Some research has evaluated guarana in combination with other ingredients. Preliminary clinical studies show that taking a specific product containing guarana 222 mg, B vitamins, vitamin C, and minerals (Berocca Boost, Bayer) can improve the speed and accuracy of visual information processing, working memory, and attention, as well as decrease mental fatigue, when compared to placebo (91485,91489,91491). Another specific combination product containing guarana 300 mg and other ingredients (Isoxan Actiflash, Menarini, NHS) improves reaction time by almost 600 msec for up to 90 minutes when compared with placebo or caffeine alone (91488). Conversely, a small clinical study in experienced young-adult video gamers shows that taking guarana 500 mg in combination with microalgae extract 440-880 mg daily for 30 days does not improve most measures of accuracy, reaction time, or gaming performance when compared to baseline (111360). A meta-analysis of 8 small clinical studies in healthy adults, that includes many of these studies, shows that taking a single dose of guarana 37.5-500 mg (median dose 222 mg; caffeine content 4-100 mg), alone or with other ingredients (i.e., B vitamins, vitamin C), within 360 minutes before a cognitive task does not improve overall cognitive performance or accuracy, but modestly improves reaction time when compared with placebo. In addition, cognitive performance was not related to guarana dose (111359). The validity of this analysis is limited by the heterogeneity of the included studies which utilized widely varying doses and various cognitive tests.
• Dysmenorrhea. Although there has been interest in using oral guarana for dysmenorrhea, there is insufficient reliable information about the clinical effects of guarana for this condition.
• Dyspepsia. Although there has been interest in using oral guarana for dyspepsia, there is insufficient reliable information about the clinical effects of guarana for this purpose.
• Erectile dysfunction (ED). Oral guarana has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: In middle-aged patients with ED, preliminary clinical research shows that taking two capsules of a specific combination product (Revactin, MD Concepts LLC) containing guarana 125 mg, muira puama 125 mg, ginger root 125 mg, and L-citrulline 400 mg twice daily for 3 months improves scores related to erectile function and intercourse satisfaction, but not sexual desire or orgasmic function, when compared to baseline (103224). The validity of this study is limited by the lack of a placebo control, the use of per-protocol analysis, and a high dropout rate. In fact, 44% of patients withdrew in order to resume use of phosphodiesterase type 5 (PDE5) inhibitors. Further, it is unclear if these effects are due to guarana, other ingredients, or the combination.
• Fatigue. Although there has been interest in using oral guarana for fatigue, there is insufficient reliable information about the clinical effects of guarana for this purpose.
• Headache. Although there has been interest in using oral guarana for headache, there is insufficient reliable information about the clinical effects of guarana for this purpose.
• Obesity. Oral guarana has only been evaluated in combination with other ingredients; its effect when used alone is unclear. Details: One very small exploratory clinical study in overweight females shows that taking guarana 855 mg, yerba mate 1008 mg, and damiana 325 mg in divided doses daily for up to 45 days delays gastric emptying, increases satiety, and modestly improves weight loss when compared to baseline (11866). The validity of these findings is limited by the small study size and lack of a comparator group.
• Psychological well-being. It is unclear if oral guarana is beneficial for improving feelings of well-being. Details: Preliminary clinical research shows that taking guarana 1080 mg daily after breakfast for 5 days does not improve feelings of well-being or mood in healthy individuals (91490).
• Radiation-induced fatigue. It is unclear if oral guarana is beneficial for improving fatigue related to radiation therapy. Details: A small clinical trial shows that taking guarana 75 mg daily does not improve symptoms of depression or fatigue when compared with placebo in patients with breast cancer undergoing radiation therapy treatments (91481).

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LIKELY SAFE ...when consumed in amounts typically found in foods. Guarana has Generally Recognized as Safe (GRAS) status for use in foods in the US (4912).

POSSIBLY SAFE ...when used orally and appropriately, short-term (12). Guarana contains caffeine. According to a review by Health Canada, and a subsequent large meta-analysis conducted in the US, doses of caffeine up to 400 mg daily are not associated with significant adverse cardiovascular, bone, behavioral, or reproductive effects in healthy adults (11733,98806). The US Dietary Guidelines Advisory Committee states that there is strong and consistent evidence that consumption of caffeine 400 mg daily is not associated with increased risk of major chronic diseases, such as cardiovascular disease or cancer, in healthy adults (98806).

POSSIBLY UNSAFE ...when used orally long-term or in high doses. Guarana contains a significant amount of caffeine. Chronic use, especially in large amounts, can produce tolerance, habituation, psychological dependence, and other significant adverse effects. Acute use of high doses, typically above 400 mg per day, has been associated with significant adverse effects such as tachyarrhythmias and sleep disturbances (11832,95503,98806). These effects would not be expected to occur with the consumption of decaffeinated guarana.

LIKELY UNSAFE ...when used orally in very high doses. The fatal acute oral dose of caffeine is estimated to be 10-14 grams (150-200 mg per kilogram). Serious toxicity can occur at lower doses depending on variables in caffeine sensitivity such as smoking, age, or prior caffeine use (11832,54425).

PREGNANCY: POSSIBLY SAFE
when consumed in amounts commonly found in foods. Due to the caffeine content of guarana, intake should be closely monitored during pregnancy to ensure moderate consumption. Although it is not considered a teratogen, caffeine crosses the placenta and causes dose-dependent increases in fetal blood concentrations (4260). The use of caffeine during pregnancy is controversial; however, moderate consumption has not been associated with clinically important adverse fetal effects (2708,2709,2710,2711,9606,11733,16014,16015,98806). In some studies, consuming amounts over 200 mg daily is associated with a significantly increased risk of miscarriage (16014). This increased risk may be most likely to occur in individuals with genotypes that confer a slow rate of caffeine metabolism (98806). According to a review by Health Canada, and a subsequent large meta-analysis conducted in the US, caffeine can be safely consumed in doses up to 300 mg daily without an increased risk of spontaneous abortion, stillbirth, preterm birth, fetal growth retardation, or congenital malformations (11733,98806). However, some research has also found that intrauterine exposure to even modest amounts of caffeine, based on maternal blood levels during the first trimester, is associated with a shorter stature in children ages 4-8 years (109846). Advise individuals to keep caffeine consumption below 300 mg daily during pregnancy.

PREGNANCY: POSSIBLY UNSAFE
when used orally in amounts over 300 mg daily. Although it is not considered a teratogen, caffeine crosses the placenta and causes dose-dependent increases in fetal blood concentrations (4260,98806). Consumption of caffeine in amounts over 300 mg daily is associated with a significantly increased risk of miscarriage in some studies (16014,98806). Advise keeping caffeine consumption from all sources below 300 mg daily. High maternal doses of caffeine throughout pregnancy have resulted in symptoms of caffeine withdrawal in newborn infants (9891). High doses of caffeine have also been associated with spontaneous abortion, premature delivery, and low birth weight (2709,2711).

LACTATION: POSSIBLY SAFE
when used orally in amounts commonly found in foods. Due to the caffeine content of guarana, intake should be closely monitored when breast-feeding. Breast milk concentrations of caffeine are thought to be approximately 50% of serum concentrations (9892).

LACTATION: POSSIBLY UNSAFE
when used orally in large amounts. Consumption of guarana might cause irritability and increased bowel activity in nursing infants (6026). Large doses or excessive intake of guarana should be avoided when breast-feeding.

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ADENOSINE (Adenocard) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, guarana might decrease the vasodilatory effects of adenosine and interfere with its use prior to stress testing.  Details Guarana contains caffeine. Caffeine is a competitive inhibitor of adenosine at the cellular level. However, caffeine does not seem to affect supplemental adenosine because high interstitial levels of adenosine overcome the antagonistic effects of caffeine (11771). It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests (11770). However, methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing (11771).

ALCOHOL (Ethanol) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, alcohol might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Concomitant use of alcohol can increase caffeine serum concentrations and the risk of caffeine adverse effects. Alcohol reduces caffeine metabolism (6370).

ANTICOAGULANT/ANTIPLATELET DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.  Details In vitro and animal research suggests that guarana extract can inhibit platelet aggregation (54378,54388,54435). This effect may be due to the caffeine in guarana, which is also reported to have antiplatelet activity (8028,8029). This interaction has not been reported in humans.

ANTIDIABETES DRUGS Interaction Rating = Minor Be watchful with this combination. Severity = Moderate •  Occurrence = Unlikely •  Level of Evidence = B Theoretically, taking guarana with antidiabetes drugs might interfere with blood glucose control.  Details Some conflicting reports claim that caffeine, a constituent of guarana, might increase or decrease blood sugar (6024,8646).

BETA-ADRENERGIC AGONISTS Interaction Rating = Moderate Be cautious with this combination. Severity = Mild •  Occurrence = Probable •  Level of Evidence = D Theoretically, concomitant use might increase the clinical effects of beta-adrenergic agonists.  Details Guarana contains caffeine. Theoretically, concomitant use of large amounts of caffeine might increase cardiac inotropic effects of beta-agonists (15).

CARBAMAZEPINE (Tegretol) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might reduce the effects of carbamazepine and increase the risk for convulsions.  Details Animal research suggests that taking caffeine can lower the anticonvulsant effects of carbamazepine and can induce seizures when given to animals in doses above 400 mg/kg (23559,23561). Human research has shown that taking caffeine 300 mg in three divided doses along with carbamazepine 200 mg reduces the bioavailability of carbamazepine by 32% and prolongs the plasma half-life of carbamazepine two-fold in healthy individuals (23562).

CIMETIDINE (Tagamet) Interaction Rating = Moderate Be cautious with this combination. Severity = Mild •  Occurrence = Likely •  Level of Evidence = B Theoretically, concomitant use might increase the effects and adverse effects of caffeine in guarana.  Details Guarana contains caffeine. Cimetidine decreases the rate of caffeine clearance by 31% to 42% (11736).

CLOZAPINE (Clozaril) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = B Theoretically, guarana might increase the levels and adverse effects of clozapine and acutely exacerbate psychotic symptoms.  Details Guarana contains caffeine. Caffeine can increase the effects and toxicity of clozapine. Caffeine doses of 400-1000 mg per day inhibit clozapine metabolism (5051). Clozapine is metabolized by cytochrome P450 1A2 (CYP1A2). Researchers speculate that caffeine might inhibit CYP1A2. However, there is no reliable evidence that caffeine affects CYP1A2. There is also speculation that genetic factors might make some patients more sensitive to the interaction between clozapine and caffeine (13741).

CONTRACEPTIVE DRUGS Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, concomitant use might increase the effects and adverse effects of caffeine found in guarana.  Details Guarana contains caffeine. Oral contraceptives decrease the rate of caffeine clearance by 40% to 65% (2714,11737).

CYTOCHROME P450 1A2 (CYP1A2) INHIBITORS Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Caffeine is metabolized by the CYP1A2 enzyme. Theoretically, drugs that inhibit CYP1A2 may decrease the rate of caffeine clearance and increase caffeine levels (5051,11741).

DIPYRIDAMOLE (Persantine) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Theoretically, guarana might decrease the vasodilatory effects of dipyridamole and interfere with its use prior to stress testing.  Details Guarana contains caffeine. Caffeine might inhibit dipyridamole-induced vasodilation (11770,11772). It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests (11770). Methylxanthines appear more likely to interfere with dipyridamole than adenosine-induced stress testing (11771).

DISULFIRAM (Antabuse) Interaction Rating = Moderate Be cautious with this combination. Severity = Mild •  Occurrence = Probable •  Level of Evidence = D Theoretically, disulfiram might increase the risk of adverse effects from caffeine.  Details In human research, disulfiram decreases the clearance and increases the half-life of caffeine (11840).

DIURETIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, using guarana with diuretic drugs might increase the risk of hypokalemia.  Details Guarana contains caffeine. Caffeine, especially in excessive amounts, can reduce potassium levels due to stimulation of the sodium-potassium pump (23579,37905,37953,38003,38034). Diuretics can also lower potassium levels.

EPHEDRINE Interaction Rating = Major Do not take this combination. Severity = High •  Occurrence = Probable •  Level of Evidence = D Theoretically, concomitant use might increase the risk for stimulant adverse effects.  Details Guarana contains caffeine. Use of ephedrine with caffeine can increase the risk of stimulatory adverse effects. There is evidence that using ephedrine with caffeine might increase the risk of serious life-threatening or debilitating adverse effects such as hypertension, myocardial infarction, stroke, seizures, and death (1275,6486,10307).

ESTROGENS Interaction Rating = Moderate Be cautious with this combination. Severity = Mild •  Occurrence = Probable •  Level of Evidence = B Theoretically, estrogens might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Estrogen inhibits caffeine metabolism (2714).

ETHOSUXIMIDE (Zarontin) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might reduce the effects of ethosuximide and increase the risk for convulsions.  Details Guarana contains caffeine. Animal research shows that caffeine 92.4 mg/kg can decrease the anticonvulsant activity of ethosuximide (23560). This effect has not been observed in humans.

FELBAMATE (Felbatol) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might reduce the effects of felbamate and increase the risk for convulsions.  Details Guarana contains caffeine. Animal research shows that a high dose of caffeine 161.7 mg/kg can decreases the anticonvulsant activity of felbamate (23563). This effect has not been observed in humans.

FLUCONAZOLE (Diflucan) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, fluconazole might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Fluconazole decreases caffeine clearance by approximately 25% (11022).

FLUTAMIDE (Eulexin) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, guarana might increase the levels and adverse effects of flutamide.  Details Guarana contains caffeine. In vitro evidence shows that caffeine can inhibit the metabolism of flutamide (23553). However, this effect has not been reported in humans.

FLUVOXAMINE (Luvox) Interaction Rating = Moderate Be cautious with this combination. Severity = Mild •  Occurrence = Probable •  Level of Evidence = D Theoretically, fluvoxamine might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Fluvoxamine reduces caffeine metabolism (6370).

LITHIUM Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, abrupt guarana withdrawal might increase the levels and adverse effects of lithium.  Details Guarana contains caffeine. Theoretically, abrupt caffeine withdrawal might increase serum lithium levels. There are two case reports of lithium tremor that worsened upon abrupt coffee withdrawal (609,610).

METFORMIN (Glucophage) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, metformin might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Animal research shows that metformin can reduce caffeine metabolism (23571). However, this effect has not been reported in humans.

METHOXSALEN (Oxsoralen) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, methoxsalen might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Methoxsalen can reduce caffeine metabolism (23572).

MEXILETINE (Mexitil) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, mexiletine might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Mexiletine can decrease caffeine elimination by 50% (1260,11741).

MONOAMINE OXIDASE INHIBITORS (MAOIs) Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use might increase the risk of a hypertensive crisis.  Details Guarana contains caffeine. Caffeine has been shown to inhibit MAO-A and -B in laboratory studies (37724,37877,37912,38108). Concomitant intake of large amounts of caffeine with MAOIs might precipitate a hypertensive crisis (15). In a case report, a patient that consumed 10-12 cups of caffeinated coffee and took the MAOI tranylcypromine presented with severe hypertension (91086). Hypertension was resolved after the patient switched to drinking decaffeinated coffee.

NICOTINE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = D Theoretically, concomitant use might increase the risk of hypertension.  Details Guarana contains caffeine. Concomitant use of caffeine and nicotine has been shown to have additive cardiovascular effects, including increased heart rate and blood pressure. Blood pressure was increased by 10.8/12.4 mmHg when the agents were used concomitantly (36549).

PENTOBARBITAL (Nembutal) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, guarana might decrease the effects of pentobarbital.  Details Guarana contains caffeine. In vivo evidence suggests that caffeine can negate the hypnotic effects of pentobarbital in humans (13742). However, animal research suggests that guarana does not alter the hypnotic effect of pentobarbital (54419).

PHENOBARBITAL (Luminal) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might reduce the effects of phenobarbital and increase the risk for convulsions.  Details Guarana contains caffeine. Animal research shows that caffeine can decrease the anticonvulsant activity of phenobarbital (23558,23559,23561). The exact mechanism of this interaction is unclear.

PHENOTHIAZINES Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, phenothiazines might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Phenothiazines can reduce the metabolism of caffeine by inhibiting cytochrome P450 1A2 (CYP1A2) (23573,23574).

PHENYLPROPANOLAMINE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Theoretically, phenylpropanolamine might increase the risk of hypertension, as well as the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Concomitant use of phenylpropanolamine and caffeine might cause an additive increase in blood pressure (11738). Phenylpropanolamine also seems to increase caffeine serum levels (13743).

PHENYTOIN (Dilantin) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might reduce the effects of phenytoin and increase the risk for convulsions.  Details Guarana contains caffeine. Animal research shows that caffeine can decrease the anticonvulsant activity of phenytoin (23559,23561). The effect does not seem to be related to the seizure threshold-lowering effects of caffeine. However, the exact mechanism of this interaction is unclear.

PIOGLITAZONE (Actos) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might increase the levels and clinical effects of pioglitazone.  Details Guarana contains caffeine. Animal research suggests that caffeine can modestly increase the maximum concentration, area under the curve, and half-life of pioglitazone, and also reduce its clearance. This increased the antidiabetic effects of pioglitazone (108812). However, the exact mechanism of this interaction is unclear.

QUINOLONE ANTIBIOTICS Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, quinolone antibiotics might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Theoretically, concomitant use might increase serum caffeine concentrations and the risk of adverse effects. Quinolones (also called fluoroquinolones) can decrease caffeine clearance by inhibiting the cytochrome P450 1A2 enzyme (606,607,608,23554,23555,23556).

RILUZOLE (Rilutek) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use might increase the levels and adverse effects of both caffeine and riluzole.  Details Guarana contains caffeine. Caffeine and riluzole are both metabolized by cytochrome P450 1A2 (CYP1A2), and concomitant use might reduce the metabolism of one or both agents (11739).

STIMULANT DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concomitant use might increase stimulant adverse effects.  Details Guarana contains caffeine. Due to the central nervous system (CNS) stimulant effects of caffeine, concomitant use with stimulant drugs can increase the risk of adverse effects (11832).

TERBINAFINE (Lamisil) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = B Theoretically, terbinafine might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. Terbinafine decreases the clearance of intravenous caffeine by 19% (11740).

THEOPHYLLINE Interaction Rating = Moderate Be cautious with this combination. Severity = Mild •  Occurrence = Probable •  Level of Evidence = D Theoretically, guarana might increase the levels and adverse effects of theophylline.  Details Guarana contains caffeine. Large amounts of caffeine might decrease theophylline clearance by 23% to 29% (11741).

TIAGABINE (Gabitril) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might increase the levels and adverse effects of tiagabine.  Details Guarana contains caffeine. Animal research shows that chronic caffeine administration can increase the serum concentrations of tiagabine. However, concomitant use does not seem to reduce the antiepileptic effects of tiagabine (23561).

TICLOPIDINE (Ticlid) Interaction Rating = Minor Be watchful with this combination. Severity = Mild •  Occurrence = Possible •  Level of Evidence = D Theoretically, ticlopidine might increase the levels and adverse effects of caffeine.  Details Guarana contains caffeine. In vitro evidence shows that ticlopidine can inhibit the metabolism of caffeine (23557). However, this interaction has not been reported in humans.

VALPROATE Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, guarana might reduce the effects of valproate and increase the risk for convulsions.  Details Guarana contains caffeine. Animal research shows that caffeine can decrease the anticonvulsant activity of valproate (23558,23559,23561,37882). The exact mechanism of this interaction is unclear.

VERAPAMIL (Calan, others) Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, verapamil might increase the levels and adverse effects of caffeine.  Details Verapamil increases plasma caffeine concentrations by 25% (11741).

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General ...Orally, guarana is typically well tolerated when used in moderation. Due to its caffeine content, use of large doses may be unsafe.
Most Common Adverse Effects:
Orally: Stomach burning and nausea.

Cardiovascular ...Orally, a case of premature ventricular contraction has been reported for a 51-year-old female who used guarana as part of a multi-ingredient herbal product (54372).
Guarana contains caffeine. Although acute administration of caffeine can increase blood pressure, regular consumption does not seem to increase either blood pressure or pulse, even in mildly hypertensive patients (1451,1452,2722). Also, epidemiological research suggests there is no association between caffeine consumption and increased incidence of hypertension. Habitual coffee consumption doesn't seem to be related to hypertension, but habitual consumption of sugared or diet cola is associated with development of hypertension (13739).
Combining ephedra with guarana can increase the risk of adverse effects. Cases of hypertension and chest pain have been reported for patients who took products containing guarana and ephedra (8644,54376). A case of cerebral infarction has also been reported for a patient consuming ephedra extract and guarana (48746). There is also a report of ischemic stroke in an athlete who consumed ephedra 40-60 mg, creatine monohydrate 6 grams, caffeine 400-600 mg, and a variety of other supplements daily for six weeks (1275).

Dermatologic ...Guarana contains caffeine. There are several case reports of urticaria after caffeine ingestion (36546,36448,36475).

Endocrine ...Guarana contains caffeine. Some evidence shows caffeine is associated with fibrocystic breast disease, breast cancer, and endometriosis; however, this is controversial since findings are conflicting (8043). Restricting caffeine in people with fibrocystic breast conditions doesn't seem to affect breast nodularity, swelling, or pain (8996). A population analysis of the Women's Health Initiative observational study has found no association between consumption of caffeine-containing beverages and the incidence of invasive breast cancer in models adjusted for demographic, lifestyle, and reproductive factors (108806). Also, a dose-response analysis of 2 low-quality observational studies has found that high consumption of caffeine is not associated with an increased risk of breast cancer (108807).
Although the effects of guarana alone are not clear, the combination of guarana along with ephedra has been reported to cause increased blood glucose levels and decreased blood levels of potassium (54376).

Gastrointestinal ...Orally, guarana can cause a sensation of burning in the stomach and vomiting (54414,91487). These effects may be due to caffeine in guarana. Orally, caffeine can cause gastric irritation, nausea, and vomiting (11832,11838,13735). In infants, caffeine may also cause feeding intolerance and gastrointestinal irritation (6023).

Immunologic ...Guarana contains caffeine. When taken orally, caffeine can cause anaphylaxis in sensitive individuals, although true IgE-mediated caffeine allergy seems to be relatively rare (11315).

Musculoskeletal ...In a clinical trial of guarana extract, one person abandoned treatment due to symptoms of arthritis with edema. It is not clear if this adverse effect is due to guarana (91487).
Cases of rhabdomyolysis and myoglobinuria have been reported in individuals that have taken products containing guarana in combination with ephedra and other herbal products. These adverse effects are thought to be related to the caffeine content of guarana (19154,36466).
Epidemiological evidence regarding the relationship between caffeine use and the risk for osteoporosis is contradictory. Caffeine can increase urinary excretion of calcium (2669,10202,11317). Women identified with a genetic variant of the vitamin D receptor appear to be at an increased risk for the detrimental effect of caffeine on bone mass (2669). However, moderate caffeine intake, less than 300 mg per day, does not seem to significantly increase osteoporosis risk in most postmenopausal women with normal calcium intake (2669,6025,10202,11317).

Neurologic/CNS ...Orally, guarana can cause dizziness (91483). The caffeine in guarana can cause insomnia (especially in children), nervousness, restlessness, dizziness, tremors, delirium, and convulsions. Other symptoms include headache, anxiety, and agitation (10755,11832,11838,13735,108016).
Taking guarana with ephedra can cause insomnia, irritability, dizziness, and headache (3719). The combination of ephedra and caffeine in guarana might also increase the risk of adverse effects such as jitteriness, seizures, and temporary loss of consciousness (2729,21015).

Ocular/Otic ...Guarana contains caffeine. When taken orally, caffeine can cause ringing in the ears (11832,11838,13735).

Psychiatric ...In a clinical trial, depression was reported by one person taking guarana extract (91483).

Renal ...Guarana contains caffeine. When taken orally, caffeine can cause diuresis (11832,11838,13735).

Other ...Guarana contains caffeine. The existence or clinical importance of caffeine withdrawal is controversial. Some researchers think that if it exists, it appears to be of little clinical significance (11839). Other researchers suggest symptoms such as headache; tiredness and fatigue; decreased energy, alertness, and attentiveness; drowsiness; decreased contentedness; depressed mood; difficulty concentrating; irritability; and lack of clear-headedness are typical of caffeine withdrawal (13738). Withdrawal symptoms such as delirium, nausea, vomiting, rhinorrhea, nervousness, restlessness, anxiety, muscle tension, muscle pains, and flushed face have been described. However, these symptoms may be from nonpharmacological factors related to knowledge and expectation of effects. Clinically significant symptoms caused by caffeine withdrawal may be uncommon (2723,11839).

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