Safety, interactions

Although the FDA has not evaluated guarana for safety, efficacy, or purity, this herb is not recommended for people who have heart disease, renal disease, hyperthyroidism, anxiety, or nervous disorders.8 It is also not advised for children or for women who are pregnant or lactating.

If taken in conjunction with any other stimulant, serious side effects, such as tachycardia, have been known to occur. A report in the Journal of Herbal Pharmacotherapy describes a case of premature ventricular contractions associated with the use of two herbal supplements that both contained large quantities of guarana.9 Other possible side effects include loss of appetite; heartburn; constipation or diarrhea; irritability; sleeplessness; irregular heartbeats; or headache.9

Perhaps one of the most serious adverse effects is guarana’s antiplatelet action and its ability to potentiate warfarin. Distinct platelet aggregation inhibition has been shown both in vitro and in vivo.10 In addition, Iyadurai and Chung report four cases of new-onset seizures that were directly related to consumption of large quantities of energy drinks containing guarana.11


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How supplied

Guarana is an ingredient in some canned or bottled soft drinks and is available as a powder to be mixed with water or another beverage.  

Summary

Guarana offers no safe, useful addition to current therapies for either weight loss or stimulation. In light of its significant and wide-ranging adverse-effect profile, guarana is not recommended as a diet supplement.
However, limited consumption of beverages containing small amounts of guarana is as safe as a daily espresso. A lethal quantity of caffeine is said to be a single dose of 10 g. As an ounce of espresso has about 65 mg of caffeine and an ounce of strong guarana contains about 44 mg of guaranine, it is unlikely that anyone would unwittingly consume a lethal amount of guarana.

References
1. Guarana. Facts & fiction.
2. Grieve M. A modern herbal: guarana.
3. Paajanen S. What is guarana?
4. Haskell CF, Kennedy DO, Wesnes KA, et al. A double-blind, placebo-controlled, multi-dose evaluation of the acute behavioural effects of guarana in humans. J Psychopharmacol. 2007;21:65-70.
5. Espinola EB, Dias RF, Mattei R, Carlini EA. Pharmacological activity of Guarana (Paullinia cupana Mart.) in laboratory animals. J Ethnopharmacol. 1997;55:223-229.
6. Lima WP, Carnevali LC Jr, Eder R, et al. Lipid metabolism in trained rats: effect of guarana (Paullinia cupana Mart.) supplementation. Clin Nutr. 2005;24:1019-1028.
7. Majhenic L, Skerget M, Knez Z. Antioxidant and antimicrobial activity of guarana seed extracts. Food Chem. 2007; 104:1258-1268.
8. Guarana.
9. Baghkhani L, Jafari M. Cardiovascular adverse reactions associated with Guarana: is there a causal effect? J Herb Pharmacother. 2002;2:57-61.
10. Bydlowski SP, Yunker RL, Subbiah MT. A novel property of an aqueous guarana extract (Paullinia cupana): inhibition of platelet aggregation in vitro and in vivo. Braz J Med Biol Res. 1988;21:535-538.
11. Iyadurai SJ, Chung SS. New-onset seizures in adults: possible association with consumption of popular energy drinks. Epilepsy Behav. 2007;10:504-508.

All electronic documents accessed October 10, 2008.