caffeine

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caffeine

chemical compound

Also known as: trimethylxanthine

Written and fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Apr 23, 2025 • Article History

Related Topics:: drug use; tea; coffee; decaffeination; cocoa bean

On the Web:: Verywell Mind - Understanding Caffeine Side Effects (Apr. 23, 2025)

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caffeine, nitrogenous organic compound of the alkaloid group, substances that have marked physiological effects. Caffeine occurs in tea, coffee, guarana, maté, kola nuts, and cacao.

Pure caffeine (trimethylxanthine) occurs as a white powder or as silky needles, which melt at 238 °C (460 °F); it sublimes at 178 °C (352 °F) at atmospheric pressure. It is very soluble in hot water; upon cooling, the solution deposits crystals of caffeine monohydrate. Caffeine is generally less soluble in organic solvents than in hot water. It is odourless but has a bitter taste.

Caffeine is present in ground coffee in amounts ranging between 0.75 and 1.5 percent by weight. The average cup of coffee thus contains about 100 mg (0.003 ounce) of caffeine. The caffeine content of tea varies greatly depending on the strength of the tea, but it averages about 40 mg. There are also about 40 mg (0.0014 ounce) of caffeine in a 12-ounce glass of carbonated cola beverage.

Cuban coffee served in the colonial city of Trinidad, Cuba

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Why Does Too Much Caffeine Keep You Awake at Night?

Caffeine has a stimulating effect on the central nervous system, heart, blood vessels, and kidneys. It also acts as a mild diuretic. Caffeine’s potent stimulatory action makes it a valuable antidote to respiratory depression induced by drug overdose (e.g., from morphine or barbiturates). The positive effects that have been described in people who use caffeine include improved motor performance, decreased fatigue, enhanced sensory activity, and increased alertness. These positive effects may partly explain the compulsion of many adults to consume coffee or other caffeine-containing beverages as part of the morning ritual of awakening. However, caffeine intake may also produce in people such negative effects as irritability, nervousness or anxiety, jitteriness, headaches, and insomnia. By the mid-1980s decaffeinated coffee and soft drinks had become widely available, giving consumers the choice of regulating their caffeine intake while continuing to enjoy these beverages.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Rick Livingston.

energy drink

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energy drink

beverage

Written by Kara Rogers

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Mar 14, 2025 • Article History

Related Topics:: stimulant; caffeine; beverage

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energy drink, any beverage that contains high levels of a stimulant ingredient, usually caffeine, as well as sugar and often supplements, such as vitamins or carnitine, and that is promoted as a product capable of enhancing mental alertness and physical performance.

Energy drinks are distinguished from sports drinks, which are used to replace water and electrolytes during or after physical activity, and from coffee and tea, which are brewed, contain fewer ingredients, and may be decaffeinated. Energy drinks also differ from soft drinks, which either do not contain caffeine or contain relatively small amounts of caffeine. Although some energy drinks are considered beverages, others, namely those containing food additives (e.g., taurine or other amino acids), may be marketed as dietary supplements. Examples of energy drinks include Red Bull, Monster, Rockstar, NOS, and Amp.

The manufacturers of energy drinks claim that their products boost energy levels. Those claims generally have been based on proprietary formulas, in which the stimulant effects of a drink were said to be derived from the specific concoction of ingredients. Research has indicated, however, that the stimulant effects of energy drinks are due primarily to caffeine. Other ingredients, such as taurine and vitamins B₆ and B₁₂, could potentially exert biological effects but have not been known to increase energy levels; the effects of some ingredients (e.g., glucuronolactone) are unknown. Levels of vitamins and certain other additives in energy drinks often far exceed recommended daily intakes.

In the early 21st century, the safety of energy drinks was an emerging public health issue. In particular, the combined use of energy drinks and alcohol, which became popular particularly among college students, was linked to an increased likelihood of high-risk drinking behaviour (e.g., binge drinking) and increased risk of alcohol-related injury and other consequences. Studies in human subjects who consumed energy drinks revealed potentially dangerous effects on heart function and blood pressure.

Kara Rogers