How It Works
Bottom Line: Guarana contains caffeine, and therefore has stimulant effects. Scientists do not know what the long-term health effects of using guarana are.
Guarana is extracted from the seed and gum of a tree found in South America. It is commonly used in beverages because of its flavor and because it contains high levels of caffeine and other caffeine-like substances. Scientists are very familiar with how caffeine affects the body: it prolongs the action of the sympathetic nervous system (responsible for our "fight or flight" response) and therefore stimulates the brain, heart and muscles, and increases blood pressure. Caffeine is also known to slow the clotting of blood, act as a diuretic (cause water loss through increased urination), and increase blood sugar levels.
Purported Uses
As an appetite suppressant
No scientific evidence supports this use.
As a stimulant
Guarana contains caffeine, which has known stimulant effects.
To treat fatigue
Although guarana contains caffeine, no clinical trials have studied its effects against fatigue in humans.
To improve sexual performance
No scientific evidence supports this use.
Research Evidence
Two small studies conducted in Brazil looked at the effects of guarana on mental performance in healthy volunteers, with negative results.
Weight loss:The effect of a supplement containing ephedra and guarana on weight loss was examined in a randomized controlled trial with 67 overweight subjects. They were given either the active supplement (containing 72 mg of ephedra and 240 mg of caffeine) or a placebo pill every day for eight weeks. At the end of the study, subjects taking the active supplement lost an average of 8.8 lb as compared to 0.88 lb in the placebo group. Several adverse symptoms such as dry mouth, insomnia and headache were reported. It is unclear from this study if the effects were more from
ephedra or guarana, or what the long-term health effects are. Ephedra supplements should not be used because they are known to cause serious cardiac side effects, including heart attack and death.
Warnings
- This product is regulated by the FDA as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. This product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
Do Not Take If
You are taking monoamine oxidase inhibitors (MAOIs) such as isocarboxazid, phenelzine, and tranylcypromine (Guarana may cause hypertensive crisis - dangerously high blood pressure - when combined with these medications).
You are taking adenosine (Because guarana contains caffeine, it can lessen the effects of adenosine. Guarana or caffeine should not be consumed for at least 12 hours before taking adenosine).
You are taking clozapine (Because guarana contains caffeine, it can interfere with the effects of clozapine. Guarana or caffeine should not be consumed less than 40 minutes before taking clozapine).
You are taking benzodiazepines (The caffeine in guarana can lessen the sedative effects of benzodiazepines).
You are taking lithium (The caffeine in guarana can reduce the levels of lithium in your blood, thereby reducing its effectiveness).
You regularly take aspirin (The caffeine in guarana increases the absorption of aspirin in the intestines, causing higher-than-normal levels of aspirin in the blood).
You are taking ephedrine (Guarana can have additive stimulating effects).
You are taking warfarin or any other blood thinner (Guarana might increase the risk of bleeding).
You have mitral valve prolapse (The caffeine in guarana was thought to cause ventricular fibrillation in a woman with mitral valve prolapse. Use with caution).
You have high blood pressure (The caffeine in guarana can increase blood pressure. Use with caution).
You are taking acetaminophen (Tylenol™) (The caffeine in guarana can increase the activity of acetaminophen. Use with caution).
You are taking terbinafine (Lamisil®), oral contraceptives, cimetidine, verapamil, disulfiram, fluconazole, mexiletine, or quinolone antibiotics (The removal of the caffeine in guarana from your body is reduced by these medications. Therefore, the caffeine will stay in your body longer. Use with caution).
Side Effects
Diuresis (increased water lost from the body as urine)
Insomnia
Large amounts of guarana can cause anxiety, agitation, headache, irritability, nausea, fast heart rate, tremors, vomiting, diarrhea, and premature ventricular contractions.
In a woman with mitral valve prolapse, guarana was thought to cause unstoppable ventricular fibrillation.
Scientific Name
Paullinia cupana
Common Name
Guarana gum, guarana seed, zoom cocoa, Brazilian cocoa
Clinical Summary
Derived from the seed and gum from the tree. Actions of guarana are attributed primarily to its caffeine content (2) (3). This product is used mainly as an appetite suppressant, CNS stimulant, and to alleviate fatigue. There are extensive data regarding caffeine and its activity. Data from an in vitro study suggests guarana may have chemopreventive effects (11). Guarana may interact with other medications (8) (9). It should not be combined with monoamine oxidase inhibitors (e.g. tranylcypromine, phenelzine), adenosine, or anxiolytics. Additive effects and potential toxicity may occur when guarana is combined with other caffeine-containing beverages. Guarana has the potential to inhibit platelet activity. Abrupt withdrawal may result in symptoms similar to those seen with caffeine withdrawal.
Purported uses
- Appetite suppression
- Central nervous system stimulation
- Fatigue
- Sexual performance
Constituents
Caffeine 2.5-7.0%
Alkaloids: Theophylline and theobromine
Tannins: Catechutannic acid and catechol
Saponins
(1)
Mechanism of Action
The primary activity of guarana is due to its high content of caffeine. Caffeine's actions include CNS stimulation, cardiac stimulation, diuresis, increases blood pressure, inhibits platelet aggregation, skeletal muscle stimulation and hyperglycemia.
(2) (3)
Adverse Reactions
Common: Diuresis and insomnia
Toxicity: Anxiety, agitation, headache, irritability, nausea, tachycardia, tremors, vomiting, diarrhea
(3) (4) (5) (6), and premature ventricular contractions
(7)
Herb-Drug Interactions
Monoamine Oxidase Inhibitors (MAO-I): Guarana may cause hypertensive crisis when combined with isocarboxazid, phenelzine, and tranylcypromine.
Adenosine: Caffeine inhibits hemodynamic effects of adenosine. Guarana or caffeine should not be consumed for at least 12 hours prior to receiving adenosine.
Clozapine: Effects of clozapine are altered when taken less than 40 minutes after caffeine or guarana administration.
Benzodiazepines: Sedative effects of benzodiazepines may be reduced by caffeine.
Lithium: Serum levels of lithium may be decreased by caffeine.
Aspirin: Absorption and bioavailability of aspirin is increased by caffeine.
Oral contraceptives, cimetidine, verapamil, disulfiram, fluconazole, mexiletine, and quinolone antibiotics: Caffeine metabolism is inhibited.
Ephedrine: Ephedrine may increase the stimulatory effects of caffeine.
Acetaminophen (Tylenol™): Efficacy of acetaminophen may be increased. Caffeine increases the pain relieving activity of acetaminophen by 40%.
Terbinafine (Lamisil): Terbinafine decreases the rate of caffeine clearance.
(8) (9)
Lab Interactions
PT / PTT / INR may be elevated.
Blood pressure may be elevated.
(9)
Literature Summary and Critique
References
- McGuffin M. A Botanical Safety Handbook. Boca Raton (FL): CRC Press; 1997.
- Gruenwald J, et al. PDR for Herbal medicines, 2nd ed. Montvale (NJ): Medical Economics Company; 1998.
- Schulz V, et al. Rational Phytotherapy: A Physicians Guide to the Use of Herbs and Related Remedies, 3rd ed. Berlin (Germany): Springer; 1998.
- Fetrow CW, et al. Professional's Handbook of Complementary and Alternative Medicines. Philadelphia: Springhouse; 1999.
- McEvoy GK, et al. AHFS Drug Information. Bethesda (MD): ASHP; 1998.
- Brinker F. Herb Contraindications and Drug Interactions, 2nd ed. Sandy (OR): Eclectic; 1998.
- Cannon ME, Cooke CT, McCarthy JS. Caffeine-induced cardiac arrhythmia: an unrecognized danger of healthfood products. Med J Aust 2001;174:520-1.
- Robbers JE. Tyler's Herbs of Choice: The Therapeutic Use of Phytomedicinals. New York: Haworth Herbal Press; 1999.
- Wallach J. Interpretation of Diagnostic Tests: A synopsis of laboratory medicine. Boston: Little, Brown, & Company; 1992.
- Boozer CN, et al. An herbal supplement containing Ma Huang-Guarana for weight loss: a randomized, double-blind trial. Int J Obes Related Metab Disord 2001;25:316-24.
- Fukumasu H, Cristina da Silva T, Avanzo JL, et al. Chempreventive effects fo Puallinia cupana Mart var. sorbilis, the guarana, on mouse hepatocarcinogenesis. Cancer Lett 2006 20;233(1):158-64.
