Guarana is derived from the seeds of a South American tree. Because it’s high in caffeine, guarana has become a popular energy supplement.
Researchers once believed that the active ingredient of guarana was a chemical specific to the plant -- guaranine. But they later discovered that it was just caffeine. Guarana has among the highest concentrations of caffeine in any plant. It may contain up to 3.6% to 5.8% caffeine by weight. Coffee only has up to 2%.
coffee and other caffeinated beverages seem to increase alertness when consumed throughout the day. Caffeine can improve mental performance and alertness in sleep-deprived people, and guarana would logically have the same effect.