Caffeine

Caffeine, a bitter-tasting, odorless stimulant drug. Caffeine is fast-working, beginning its effects within minutes after being consumed. Acting on the central nervous system, caffeine increases the uptake of oxygen in the lungs, speeds up metabolism, and quickens the heart rate and pulse. These effects lead to enhanced alertness while decreasing drowsiness and general fatigue. Caffeine is also a diuretic, and it stimulates vasoconstriction. Vasoconstriction can help relieve vascular headaches, those caused by dilation (widening) of the blood vessels in the head. Caffeine also may increase muscular capacity and coordination. The drug is broken down and excreted from the body within a few hours.

Caffeine is found in many beverages, including coffee, tea, soda, and hot chocolate. Per average cup, coffee contains about 100 mg of caffeine; decaffeinated coffee, about 5 mg or less; tea or soda, about 50 mg; and hot chocolate, about 10 mg. Caffeine is also used in a variety of over-the-counter medications.

In high doses, such as the amount contained in four cups of coffee consumed within a short time, caffeine can cause restlessness, insomnia, irritability, and headaches. People who regularly consume caffeine can suffer withdrawal symptoms when they stop. Withdrawal symptoms may include nausea, headache, weariness, and irritability.

Caffeine is commercially produced as a byproduct of making decaffeinated coffee. It is also extracted from tea leaves and kola nuts, and can be synthesized from uric acid.