What effects do guarana and taruine from energy drink have on the human body?

Caffeine ; calming: Guarana is a main source of caffeine in energy drinks, which is a natural stimulant. I am really not sure why energy drinks have taurine, which is an Amino Acid that has a calming effect on the nervous system ; does not make people feel energetic. My best guess is that because the first energy drinks had taurine all the others have it because people now expect energy drinks to have it!see comment:.