Guarana (Paullinia cupana) is a Brazilian plant. Extracts made from its seeds, which contain caffeine, are found in food, energy drinks and supplements. Guarana was traditionally used by Amazonian Indians to increase energy and libido and suppress appetite.
Evidence is mixed about guarana’s impact on cognitive function. A small trial published in 2013 showed no evidence for improvements in well-being, anxiety and mood, while a different small trial showed guarana used with multivitamins may help improve mood and cognitive performance.
A small trial published in 2011 showed some preliminary evidence that guarana may be useful in the short-term treatment of fatigue in breast cancer patients. There is some evidence for weight loss, but the preparations used in these studies included other herbs.
Some reports have linked guarana to heart and kidney problems, high blood pressure and seizures so cautious use or avoidance is advised in those with high blood pressure or cardiac arrhythmias.
Each gram of guarana can contain 40 to 80 mg of caffeine, which may interact with many medications (including diuretics, antiplatelet drugs, stimulants and blood thinning drugs) and result in hospitalisation for caffeine overdose.
Caution is also urged if you have anxiety, diabetes or gastric ulcers.
Concentrated extracts should be stopped one week before major surgery; some research has suggested it may have anti-platelet activity, which may increase bleeding risk.
Combining guarana with alcohol can lead to a range of problems such as dehydration, severe and prolonged hangovers, and alcohol poisoning.