Caffeine is a naturally occurring stimulant found in the leaves, seeds, or fruit of over sixty plants around the world. Caffeine exists in the coffee bean in Arabia, the tea leaf in China, the kola nut in West Africa, and the cocoa bean in Mexico. Because of its use throughout all societies, caffeine is the most widely used psychoactive substance in the world. The most common caffeine sources in North America and Europe are coffee and tea. Since about 1980, extensive research has been conducted on how caffeine affects health. Most experts agree that moderate use of caffeine (300 milligrams, or about three cups of coffee, per day) is not likely to cause health problems.