Caffeine is a xanthine alkaloid compound that acts as a stimulant in humans.
The word comes from the Italian term for coffee. Caffeine is also called guaranine when found in guarana, mateine when found in mate, and theine when found in tea. It is found in the leaves and beans of the coffee plant, in tea, yerba mate, and guarana berries, the kola nut, the Yaupon Holly, and in small quantities in cocoa.
Overall, caffeine is found in the beans, leaves, and fruit of over 60 plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants.
Caffeine is a central nervous system (CNS) stimulant, having the effect of temporarily warding off drowsiness and restoring alertness.
Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks enjoy great popularity; caffeine is the world's most widely consumed psychoactive substance, but unlike most other psychoactive substances, it is legal and unregulated in nearly all jurisdictions.
In North America, 90% of adults consume caffeine daily. The U.S. Food and Drug Administration lists caffeine as a "Multiple Purpose GRAS Food Substance".
Many natural sources of caffeine also contain widely varying mixtures of other xanthine alkaloids, including the cardiac stimulants theophylline and theobromine and other substances such as polyphenols which can form insoluble complexes with caffeine.