Caffeine is a natural chemical with stimulant effects. It is found in coffee, tea, cola, cocoa, guarana, yerba mate, and over 60 other products.

Caffeine works by stimulating the central nervous system, heart, muscles, and the centers that control blood pressure. Caffeine can raise blood pressure, but might not have this effect in people who use it all the time. Caffeine can also act like a "water pill" that increases urine flow.

People most commonly use caffeine for mental alertness, headache, migraine, athletic performance, memory, and obesity. It is also used for asthma, gallbladder disease, ADHD, low blood pressure, depression, and many other conditions.