Citation metadata

Editors: K. Lee Lerner and Brenda Wilmoth Lerner
Date: 2008
The Gale Encyclopedia of Science
From: The Gale Encyclopedia of Science(Vol. 1. 4th ed.)
Publisher: Gale
Document Type: Topic overview
Pages: 3
Content Level: (Level 5)

Document controls

Main content

Full Text: 
Page 715


Caffeine, scientific name methylxanthine, is an alkaloid found in coffee, tea, chocolate, and other natural foods. It is also a component of cola soft drinks. Caffeine has been a part of the human diet for many centuries and is one of the most widely used central nervous system stimulants worldwide. In recent years, research has raised questions about possible deleterious health effects of caffeine, but no definitive conclusions have been reached about the harmfulness of moderate amounts.

Chemistry of caffeine

Caffeine’s chemical name is 3,7-dihydro-1,3,7-trimethyl-1H-purine-2, 6-dione. It is also known as theine, methyl theobromine, and 1,3,7-trimethylxanthine. Its molecular formula is C8 H10 N4 O2•H2 O, and it consists of bicyclic molecules derived from the purine ring system.

In its pure form, caffeine is a fleecy white solid or long silky crystals. It is odorless, but has a distinctive bitter taste. When heated, caffeine loses water at 176°F (80°C), sublimes at 352.4°F (178°C), and/or melts at 458.2°F (236.8°C). It is only slightly soluble in water and alcohol, but dissolves readily in chloroform. Water solutions of caffeine are essentially neutral (pH = 6.9).

Caffeine is a member of the alkaloid family, a group of compounds obtained from plants whose molecules consist of nitrogen-containing rings. In general, alkaloids tend to have identifiable physiological effects on the human body, although these effects vary greatly from compound to compound.


The use of caffeine is thought to go back as far as the Stone Age, which began about 2.5 million years ago and ended in some parts of the world only about 5,000 years ago. It would probably be safe to say that caffeine was a regular part of the human diet for thousands of years. Although the pleasures of coffee, have been known to humans for centuries, the isolation of caffeine from these beverages was accomplished only in the early 1800s. During the 1820s, researchers identified the active agents in tea and chocolate and gave them a variety of names such as guaranin. In 1840, T. Martins and D. Berthemot independently showed that these compounds are all identical with caffeine. Caffeine itself was originally called cofeine or caffein and only Page 716  |  Top of Articlein the late 1820s was given the name by which it is known today.

Much of the work leading to the full characterization of caffeine’s molecular structure was completed by German chemist Emil Fischer (1852–1919). Fischer first synthesized the compound from raw materials in 1895, and two years later derived its precise structural formula.


Of all the commercial sources of caffeine, guarana paste has the highest concentration of the pure compound, about 4%. Guarana paste is made from the seed of the Paullinia tree, found primarily in Brazil. More common sources of caffeine contain lower concentrations of the compound: 1.1 to 2.2% in coffee beans; 3.5% in tea leaves; and 1.5% in kola nuts. Other less common sources of caffeine include mate´ leaves, obtained from the Ilex plant (less than 0.7% caffeine), and yoco bark, obtained from the Paullinia yoco tree (2.7% caffeine).

Because of the way in which these foods are prepared, the above data do not give an accurate picture of the amount of caffeine that people consume. The average cup coffee, for example, contains approximately 100 to 150 mg of caffeine; the average cup of tea, 50 mg of caffeine; and the average cup of cocoa, about 5 mg of caffeine. Cola drinks tend to contain 35 to 55 mg of caffeine, and the average chocolate bar contains about 20 mg of the compound. Beginning in 1997 and continuing into the 2000s, products are increasingly introduced that contain caffeine including bottled water and chewing gum.

Pharmacological effects

The most important physiological effect of caffeine is that it stimulates nerve cells, particularly those in the brain. It appears that caffeine molecules bind to neurotransmitter receptor sites in nerve cells, causing the continual stimulation of those cells. This property explains the most common clinical symptoms of caffeine ingestion: wakefulness, excitability, increased mental awareness, and restlessness.

Caffeine affects nerve tissue in the brain much more quickly than it does nerve tissue anywhere else in the body. As a result, it will bring about muscular changes such as convulsions only with very high doses of the drug—10 g or more, the equivalent of drinking 70 to 100 cups of coffee in a short time. Death from caffeine overdose is, therefore, extremely unlikely.

Teratogenic and mutagenic effects

Concerns about the possible health effects of consuming caffeine have been expressed for well over a hundred years. Recent concern about its physiological effects tends to focus on mutagenic and teratogenic effects. Mutagenic effects are those that change the reproductive genes, producing mutations in subsequent generations. Scientific reports have also appeared connecting the consumption of large doses of caffeine with particular types of cancer. However, the significance of such findings to the average coffee or tea drinker is unclear.

The situation with teratogenic effects—those that affect the fetus while it is still in the womb—is somewhat clearer. Caffeine passes readily across the placental lining, exposing the fetus to concentrations of the stimulant that are comparable to those in the mother’s blood. Since the developing nervous system of the fetus is more likely to be affected by the drug than is the mother’s, a reduction in caffeine intake is often recommended for pregnant women.

Usage, tolerance, and Interactions

People who use large amounts of caffeine over long periods of time build up a tolerance to it. When that happens, they have to use additional caffeine to receive the same effects. Heavy caffeine use can also lead to dependence. Thus, if the person stops using caffeine abruptly, withdrawal symptoms may occur. These symptoms can include throbbing headaches, fatigue, drowsiness, yawning, irritability, restlessness, vomiting, or runny nose. These symptoms can persist for as long as one week if caffeine is avoided. Then the symptoms usually disappear.

Caffeine cannot replace sleep and should not be used regularly to stay awake as the drug can lead to more serious sleep disorders, like insomnia. When determining caffeine dosage, consider how much caffeine is being consumed from all sources such as coffee, tea, chocolate, soft drinks, and other foods and drinks. Check with a pharmacist or physician to find out how much caffeine is safe to use.

Caffeine may cause problems for people with the following medical conditions: food or drug allergies, peptic ulcer, heart arrhythmias or palpitations, heart disease or recent heart attack, high blood pressure, liver disease, insomnia (trouble sleeping), anxiety or panic attacks, agoraphobia (fear of being in open places), and premenstrual syndrome (PMS).

Sidebar: HideShow

Page 717  |  Top of Article


Mutagenic—Any substance or form of energy that can bring about changes in DNA molecules, thereby leading to changes in an organism’s genetic make-up.

Pharmacological—Having to do with the properties, uses, and effects of drugs.

Teratogenic—Any substance that can bring about changes in a fetus prior to birth.

At recommended doses, caffeine can sometimes cause restlessness, irritability, nervousness, shakiness, headache, lightheadedness, sleeplessness, nausea, vomiting, and upset stomach. At higher than recommended doses, caffeine can cause excitement, agitation, anxiety, confusion, a sensation of light flashing before the eyes, unusual sensitivity to touch, unusual sensitivity of other senses, ringing in the ears, frequent urination, muscle twitches or tremors, heart arrhythmias, rapid heartbeat, flushing, and convulsions.

Certain drugs interfere with the breakdown of caffeine in the body. These include oral contraceptives that contain estrogen, the antiarrhythmia drug mexiletine (Mexitil®), the ulcer drug cimetidine (Tagamet®), and the drug disulfiram (Antabuse®), used to treat alcoholism. Caffeine may also interfere with the body’s absorption of iron. Anyone who takes iron supplements should take them at least an hour before or two hours after using caffeine.



Banks, Mary. The World Encyclopedia of Coffee. London, UK: Lorenz, 2002.

Cowan, Brian William. The Social Life of Coffee: The Emergence of the British Coffeehouse. New Haven, CT: Yale University Press, 2005.

Dews, Peter B., ed. Caffeine: Perspectives from Research. Berlin, Germany: Springer-Verlag, 1984.

Weinberg, Bennett Alan. The World of Caffeine: The Science and Culture of the World’s Most Popular Drug. New York: Routledge, 2001.

Wild, Antony. Coffee: A Dark History. New York: W.W. Norton, 2005.

David E. Newton

Source Citation

Source Citation   

Gale Document Number: GALE|CX2830100393