Also known as “Brazilian cocoa,” guarana is a South American plant whose seeds’ caffeine content is a whopping two-to-five times that of coffee beans. The amount of guarana in energy drinks varies wildly, from just 1 or 2 mg to 300 mg. Importantly, energy drinks do not include guarana in their labels’ caffeine totals. So if the label reads “Caffeine + guarana,” that means a super-sized—and unspecified—dose of caffeine.
The New York Times published an extensive article on ingredients such as guarana and ginseng in 2013, under the headline, “Energy Drinks Promise Edge, but Experts Say Proof Is Scant,” in which author Barry Meier notes that “the energy drink industry is based on a brew of ingredients that, apart from caffeine, have little, if any benefit for consumers.”
Commonly reported guarana side effects include restlessness, nervousness, increased heart rate, insomnia, headaches, nausea, heartburn and loss of appetite. People with pre-existing conditions like heart disease, high blood pressure, kidney disease, overactive thyroid or diabetes should not consume guarana. The risks of side effects only increase when guarana is combined with caffeine, yet, energy drink companies do not warn consumers about what’s in their beverages.