A reputed stimulant, guarana gives you more than just an increase in physical endurance and stamina; it also carries properties that can help in digestion, weight loss and pain relief. Guarana is a creeping shrub that is native to northern Brazil and Venezuela in the Amazon rainforest. Its fruit are bright red and small, and contains black seeds. Its seeds are rich in caffeine, containing up to 4 to 8 caffeine, which is more than the 1 to 2.5 caffeine found in coffee beans. The seeds are also teeming with tannins and xanthine alkaloids, theobromine and theophylline.