Caffeine is trimethylxanthine (C8H10N4O2). It’s an addictive stimulant that operates in the brain the same way amphetamines, cocaine and heroin do although it is much milder. At least half of all American adults consume more than 300 milligrams of caffeine every day which making it America’s most popular drug by far. The caffeine comes in many different products like coffee, tea, cola, chocolate, and many other products.