The most widely consumed mind-altering drug in the world, caffeine intake is a part of the daily lives of millions of people across the globe. Though relatively harmless, the effects of caffeine are distinct, as is demonstrated by the great number of people who depend upon coffee to help them wake-up in the early morning.

In addition to coffee, caffeine occurs naturally in tea, kola nuts, and ilex plants, as well as cocoa in small amounts. The substance can, however, also be prepared synthetically from uric acid and added to various consumables. In pure form it is odorless, somewhat bitter in taste, white, powdery, and soluble in water. The substance is also rapidly absorbed by the body, which distributes the caffeine through all of its tissues and fluids, producing a stimulating effect on the central nervous system, heart, kidneys, and blood vessels. The body rids itself of caffeine through metabolism and urination.

When consumed in moderation, caffeine can help restore mental alertness, prevent fatigue, enhance motor activity, and produce a general feeling of well being. These are the effects that one might experience from a regular cup of coffee, which roughly contains 100 milligrams of the stimulant. Yet, reactions vary and some people exhibit high levels of sensitivity to the substance. When one intakes too great a quantity of caffeine, adverse effects may occur, including restlessness, insomnia, tremor, headaches, irritability, and irregular heartbeat. Due to an increased awareness of this possibility, many traditional caffeine-containing products, such as colas, coffee, and tea, are now offered in decaffeinated varieties.