Caffeine is an alkaloid drug, associated with tea and coffee but is also present in small amounts in chocolate. It has a stimulant action, particularly on the central nervous system and the heart. In humans caffeine is demethylated into theophylline, theobromine and paraxanthine.
It promotes wakefulness and increases mental activity. However it is also a diuretic and causes headaches, and can cause constriction in some vascular blood vessels.
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