Caffeine is the world's most popular drug. The white, bitter-tasting, crystalline substance was first isolated from coffee in 1820. Both words, caffeine and coffee, are derived from the Arabic word qahweh (pronounced "kahveh" in Turkish). The origins of the words reflect the spread of the beverage into Europe via Arabia and Turkey from north-east Africa, where coffee trees were cultivated in the 6th century. Coffee began to be popular in Europe in the 17th century. By the 18th century plantations had been established in Indonesia and the West Indies.
The caffeine content of coffee beans varies according to the species of the coffee plant. Beans from Coffee arabica, grown mostly in Central and South America, contain about 1.1% caffeine. Beans from Coffee robusta, grown mostly in Indonesia and Africa, contain about 2.2% caffeine. Caffeine also occurs in cacao pods and hence in cocoa and chocolate products; in kola nuts, used in the preparation of cola drinks; and in the ilex plant, from whose leaves the popular South American beverage yerba mate is prepared.
Caffeine is also found in tea. It was first isolated from tea leaves in 1827 and named "theine" because it was believed to be a distinctly different compound from the caffeine in coffee. Tea leaves contain about 3.5% caffeine, but a cup of tea usually contains less caffeine than a cup of coffee because much less tea than coffee is used during preparation.
Caffeine taken in beverage form begins to reach all tissues of the body within five minutes. Peak blood levels are reached in about 30 minutes. Half of a given dose of caffeine is metabolized in about four hours ? more rapidly in smokers and less rapidly in newborn infants, in women in late pregnancy, and in sufferers from liver disease. Normally, almost all ingested caffeine is metabolized. Less than 3% appears unchanged in urine, and there is no day-to-day accumulation of the drug in the body.
Short-term effects of a drug are those that appear soon after a single dose and disappear within hours. Ingestion of the amount of caffeine in one or two cups of coffee (75-150 mg) causes many mild physiological effects. General metabolism increases - expressed as an increase in activity or raised temperature, or both. The rate of breathing increases, as does urination and the levels of fatty acids in the blood and of gastric acid in the stomach. (However, at least one other component of coffee also increases gastric acid secretion. Therefore ulcer sufferers may not achieve relief by switching to decaffeinated coffee.)
Caffeine use may increase blood pressure.
Caffeine stimulates the brain and behavior. Use of 75-150 mg of caffeine elevates neural activity in many parts of the brain, postpones fatigue, and enhances performance at simple intellectual tasks and at physical work that involves endurance but not fine motor coordination. (Caffeine-caused tremor can reduce hand steadiness.)
Caffeine's effects on complex intellectual tasks and on mood do not lend themselves to a simple summary. The effects depend on the personality of the user, on the immediate environment, on the user's knowing whether caffeine has been taken, and even on the time of day.
The effects of caffeine on sleep are clear-cut: taken before bedtime, it usually delays sleep onset, shortens overall sleep time, and reduces the "depth" of sleep. After using caffeine, sleepers are more easily aroused, move more during sleep, and report a reduction in the quality of sleep. The effects of caffeine on dreaming are less clear.
Larger doses of caffeine, especially when given to non-users, can produce headache, jitteriness, abnormally rapid heartbeat (tachycardia), convulsions, and even delirium. Near-fatal doses cause a crisis resembling the state of a diabetic without insulin, including high levels of blood sugar and the appearance of acetone-like substances in urine. The lowest known dose fatal to an adult has been 3,200 mg - administered intravenously by accident. The fatal oral dose is in excess of 5,000 mg - the equivalent of 40 strong cups of coffee taken in a very short space of time.
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