cAffEine

Caffeine is a xanthine alkaloid compound that acts as a stimulant in humans. Caffeine is sometimes 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, guarana berries, and in small quantities in cocoa, the kola nut and the Yaupon Holly. 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 upon them. Its name is derived from the Italian caffè ("coffee") plus the alkaloid suffix -ine.

Caffeine is a central nervous system (CNS) stimulant, having the effect of warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks, enjoy popularity great enough to make caffeine the world's most widely consumed psychoactive substance. In North America, 90% of adults consume caffeine daily.

Caffeine is a plant alkaloid, found in numerous plant species, where it acts as a natural pesticide that paralyzes and kills certain insects feeding upon them. The most commonly used caffeine-containing plants are coffee, tea, and to some extent cocoa. Other, less commonly used, sources of caffeine include the yerba mate and guarana plants, which are sometimes used in the preparation of teas and energy drinks. Two of caffeine's alternative names, mateine and guaranine, are derived from the names of these plants.
The world's primary source of caffeine is the coffee bean (the seed of the coffee plant), from which coffee is brewed. Caffeine content in coffee varies widely depending on the type of coffee bean and the method of preparation used; even beans within a given bush can show variations in concentration. In general one serving of coffee ranges from about 40 milligrams for a single shot (30 milliliters) of arabica-variety espresse to about 100 milligrams for strong drip coffee. Generally, dark-roast coffee has less caffeine than lighter roasts because the roasting process reduces the bean's caffeine content. Arabica coffee normally contains less caffeine than the robusta variety. Coffee also contains trace amounts of theophylline, but no theobromine.

Tea is another common source of caffeine. Tea usually contains about half as much caffeine per serving as coffee, depending on the strength of the brew. Certain types of tea, such as black and oolong, contain somewhat more caffeine than most other teas. Tea contains small amounts of theobromine and slightly higher levels of theophylline than coffee. Preparation has a significant impact on tea, and color is a very poor indicator of caffeine content. Teas like the green Japanese gyokuro, for example, contain far more caffeine than much darker teas like lapsang souchong, which has very little.

Caffeine is a central nervous system and metabolic stimulant, and is used both recreationally and medically to reduce physical fatigue and restore mental alertness when unusual weakness or drowsiness occurs. Caffeine stimulates the central nervous system first at the higher levels, resulting in increased alertness and wakefulness, faster and clearer flow of thought, increased focus, and better general body coordination, and later at the spinal cord level at higher doses. The precise amount of caffeine necessary to produce effects varies from person to person depending on body size and degree of tolerance to caffeine. It takes less than an hour for caffeine to begin affecting the body and a mild dose wears off in three to four hours. Consumption of caffeine does not eliminate the need for sleep: it only temporarily reduces the sensation of being tired.