One of my favorite subjects.

Coffee Science Information Centre:Coffee and Caffeine Health Information

What is Caffeine?
The major pharmacologically active ingredient in coffee is the central nervous system stimulant, caffeine, known chemically as 1,3,7-trimethylxanthine. The dimethylxanthine derivatives, theophylline and theobromine, are also found in a variety of plants.

Caffeine occurs naturally in the leaves, seeds or fruit of more than 60 plant species, of which cocoa-beans, tea, coffee, cola and guarana are the most well known. Caffeine is also added to many popular carbonated drinks, and is a component of a number of pharmacological preparations and over-the-counter medications including analgesics (where caffeine acts as an adjuvant), diet aids, and cold/flu remedies. (Caffeine added to a food or drink must, by law, be included in the ingredients list). In addition, both caffeine and theophylline have bronchodilatory properties, and are used in the treatment of neonatal apnoea (inability of the newborn to breath properly).