Caffeine, also known as trimethylxanthine, coffeine, theine, mateine, guaranine, and methyltheobromine, is an alkaloid found naturally in such foods as coffee beans, tea, kola nuts, Yerba maté, guarana, and (in small amounts) cacao beans. Plants create caffeine as a pesticide, to paralyze and kill the insects feeding on them. While caffeine in its pure form is the chemical standard for bitterness, it is added to some soft drinks such as colas, Irn-Bru and Mountain Dew ostensibly for its taste.

Caffeine's main pharmacological properties are: a stimulant action on the central nervous system with psychotropic effects and stimulation of respiration, a stimulation of the heart rate, and a mild diuretic effect.

One common source of caffeine is the coffee plant, the beans from which are used to produce coffee. Caffeine content varies substantially between Arabica and Robusta species and to a lesser degree between varieties of each species. One dose of caffeine is generally considered to be 100 mg. In theory, a single serving (6 fl oz / 150 ml) of drip coffee or one-half caffeine tablet would deliver this dose. In the real world, coffee varies considerably in caffeine content per serving, ranging from about 75 mg to 250 mg.

Tea is another common source of caffeine in many cultures. Tea contains somewhat less caffeine per serving than coffee, (usually about half as much, depending on the strength of the brew), though certain types of tea, such as Lapsang sou chong smoked teas, and oolong contain less caffeine

Caffeine is also common in soft drinks such as Cola. Such drinks typically contain about 25 mg to 50 mg of caffeine per serving. Some "Energy drinks" such as Red Bull contain considerably more caffeine per serving, ranging from 100 to 400 mg.

Formal Chemical Name (IUPAC)