Guarana

Stimulant: Energy drinks, teas.
Guarana is a plant that has seeds high in caffeine. Companies add guarana to beverages as a "natural" source of caffeine, but its effect is the same as the caffeine in coffee or tea. Include guarana when you're keeping track of the caffeine in your diet. Too much caffeine from any source can cause insomnia, anxiety, and other problems (see discussion of caffeine).