Guarana (Paullinia Cupana) comes from the seed of an herb found in the Amazon regions in Brazil. Brazilian Indians have used Guarana for hundreds of years as a stimulant. The Guarana fruit is harvested when ripe, after turning bright red or yellow. The gathered fruit yields a small round black seed which is crushed into a paste containing about 10% Guaranine (caffeine).Guarana contains some substances that is claimed to slow down the uptake of caffeine in the body, thus making the effects last longer than from coffee or caffeine tablets. As usual, there haven't been any scientific studies on this. Whether it's true or not, guarana is still one of the most caffeine rich sources known. The effects of caffeine are very well documented. It stimulates the nervous system, fights fatigue and help the body use fats for fuel. It's also a thermogenic compound (it raises the body temperature).