Caffeine is one of the world's most widely used drugs.
Some anthropologists believe its use may date back to the Stone Age. Pharmacologically, caffeine is one of a group of stimulants called methylxanthine, or xanthine, that occur naturally in some plants. Cocoa, used to make chocolate, contains caffeine as well as theobromine, another xanthine. Food and beverage manufacturers are legally required to list caffeine on their products' label only when caffeine has been added. Caffeine naturally present in other ingredients used in the production process need not be on the label.