Guarana, an herb from the Amazon rain forest, has a long history of use as a stimulant beverage. It has also been used to treat arthritis, diarrhea, and headaches.

Like tea, coffee, and chocolate, guarana contains alkaloids in the caffeine family, such as theobromine and theophylline. Caffeine is known to reduce pain, treat migraine headaches, and, of course, fight fatigue. In addition, it may, under certain circumstances, enhance sports performance, improve mental function, and modestly aidweight loss.

Most of the proposed uses of guarana fall into line with these effects of caffeine. For example, in a double-blind, placebo-controlled study of 129 healthy young adults, one-time use of guarana plus vitamins and minerals improved mental function and reduced mental fatigue among those undergoing a battery of cognitive tests.7 In another double-blind, placebo-controlled study, use of guarana alone or guarana plus ginseng appeared to improve mental function(though the study suffered from some design problems)1In two other studies, no benefits were seen.2,3

Guarana has also been studied as a potential aid in fighting a common side effect of chemotherapy—fatigue.8 In one randomized trial, 75 breast cancer patients undergoing chemotherapy were randomized to receive guarana (50 mg twice daily for 21 days) or placebo. Since this trail had a crossover design , both groups received the herb and the placebo but at alternate times. At the end of the trial, researchers found evidence that guarana was helpful in reducing fatigue.

Another double-blind, placebo-controlled study tested the effects of guarana plus ephedrafor weight loss.4 In this trial, a total of 67 overweight people were given either placebo or a combination of guarana and ephedra for a period of 8 weeks. The results showed significantly greater weight loss in the treated group than in the placebo group. However, ephedra is an unsafe substance. (See the Ephedra article for more information.)