Introduction-
Caffeine is found naturally in tea, coffee, and cocoa. It is also added to many soft drinks. It is one of the few drugs -- a stimulant -- added to foods.It is a bitter white crystalline xanthine alkaloid that acts as a psychoactive stimulant drug and a mild diuretic (speeds up urine production). Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819.
Caffeine is ingested often in cases of severe migraine headaches to quickly relieve pain (acts due to its dilating effects).
Pharmacology-
Caffeine acts as CNS stimulant. The mechanism of action of caffeine requires an elaborate explanation and may be best understood from the following webpage: