A white, bitter, crystallizable substance, found in coffee and tea. It is identical with the alkaloid theine from tea leaves, and with guaranine from guarana. It is responsible for most of the stimulating effect of coffee or tea.
A naturally occurring alkaloid in coffee and, to a lesser extent, tea. It is used in medicine as a mild stimulant. A shot of espresso has the caffeine content of a can of soda. See also Decaffeination