od. It contains an ingredient called capsaicin that stimulates saliva, stimulates digestion and accelerates your metabolism at a safer level. Green Tea - This tea is a natural stimulant that behaves much like coffee but with the added benefit of vitamin C and flavoniods. You can regulate the strength of the stimulant by steeping the tea quickly or for a long time. It can be purchased in a tea bag, or loose or in capsules as well.