Caffeine 3370
Photo by: fotogiunta

Figure 1. The molecular structure of caffeine.
Figure 1. The molecular structure of caffeine.

Caffeine belongs to the family of heterocyclic compounds known as purines. It has the systematic name 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione; it is also known as 1,3,7-trimethylxanthine, and 1,3,7-trimethyl-2,6-dioxopurine. Caffeine can be classified as an alkaloid , a term used for substances produced as end products of nitrogen metabolism in some plants. The chemical formula is C 8 H 10 N 4 O 2 . Caffeine has a molar mass of 194.19 grams (6.85 ounces). It is soluble in water and in many organic solvents, and it appears in pure form as white crystals. Caffeine can be prepared by extraction from natural sources or by synthesis from uric acid.

More than sixty plants, including those that give us coffee, tea, cola, and cacao, produce caffeine from the purine xanthine. Whereas caffeine is a natural constituent in coffee, tea, chocolate, and some cola drinks, it is added to consumer products such as soft drinks, diet pills, and analgesics . Caffeine is said to be the most widely used drug in the world, and more than 100 million people in the United States consume caffeine each day. It has pharmacological uses: as a cardiac and respiratory stimulant and as an agent that promotes kidney diuresis. A therapeutic dose of caffeine is about the same as the amount found in an average cup of coffee, between 100 and 200 milligrams (0.0071 ounces). Decaffeinated coffee can be prepared through extraction with a solvent (such as methylene chloride), water extraction, or steam extraction.

Caffeine enters the bloodstream about ten minutes after its ingestion and stays in the body for up to twelve hours. Like other alkaloids, caffeine has powerful physiological effects on humans and animals. It stimulates heart muscle and relaxes certain structures that contain smooth muscle, including the coronary arteries and the bronchi. It is a diuretic. Theophylline and theobromine, two other plant alkaloid derivatives of xanthine, have physiological effects similar to those of caffeine.

Caffeine acts as a stimulant of the central nervous system (CNS) through several proposed mechanisms. The most important seems to be its interference with the ability of the neurotransmitter adenosine to bind to its nerve cell receptor . Also, caffeine inhibits the enzyme cyclic nucleotide phosphodiesterase, which breaks down intracellular cyclic adenosine monophosphate (cAMP), another messenger involved in the transmission of nerve signals from hormones originating outside the central nervous system

Coffee drinks are among the most popular sources of caffeine, believed to be the most commonly used drug worldwide.
Coffee drinks are among the most popular sources of caffeine, believed to be the most commonly used drug worldwide.

such as epinephrine and glucagon—hormones that initiate the "fight or flight" response in animals. Other proposed mechanisms have to do with effects on CNS intracellular calcium ion concentrations.

Caffeine is moderately habit-forming, but because caffeine users can usually control its use, it is not listed as an addicting stimulant by the American Psychiatric Association. Caffeine is not regarded as being harmful to the average healthy adult. In fact there are beneficial effects to be derived from moderate caffeine intake (about three cups of coffee per day). It relieves tiredness, improves thought processes, increases alertness, and enhances physical performance. It may be used to treat respiratory depression and, because it constricts blood vessels in the brain, is often an ingredient in headache remedies. There is some evidence that caffeine may help to mitigate symptoms of migraine headache and lower the risk of gallstones. Some studies show that caffeine may protect against Parkinson's disease, perhaps by inhibiting the depletion of the neurotransmitter dopamine in brain cells.

There may be some adverse effects due to excessive caffeine intake, such as restlessness, headaches, heart palpitations, heartburn, and insomnia. Some individuals may have a toxic reaction to it. Ingestion by pregnant women and nursing mothers may have adverse effects on fetuses and babies; caffeine crosses the placenta and gets into breast milk. Caffeine has a wide margin of safety. A lethal dose for most people would be the amount of caffeine found in about one hundred cups of coffee.

Some investigations into caffeine-related health issues are inconclusive. Studies have shown no correlation between caffeine intake and increased risk of osteoporosis or increased risk of spontaneous abortion. There is no conclusive evidence linking caffeine intake (as coffee) with bladder, pancreatic, breast, or colon cancer. There is also no conclusive evidence that moderate caffeine intake contributes to heart disease or heart arrhythmias; however, one study has shown that relatively high coffee consumption elevates blood levels of homocysteine (an amino acid)—a situation that may contribute to heart attack or Alzheimer's disease. There is continuing controversy over whether heavy caffeine intake increases blood pressure, a woman's risk of developing breast lumps, or the incidence of miscarriage.

SEE ALSO Dopamine ; Epinephrine ; Stimulants .

Sharron W. Smith


"Coffee: How Much Is Too Much?" (2001). Consumer Reports (May): 64–65.

Other Resources

Merck Index , 12th edition. CD-ROM Version 12:1. (1996). London: Chapman and Hall.

Caffeine Archive. Available from .

User Contributions:

Comment about this article, ask questions, or add new information about this topic: