Caffeine is a mild alkaloid stimulant made by some plants. It is found in coffee beans, tea leaves, and cocoa beans. It is added to soft drinks, energy drinks, and energy bars; and sold in capsules and tablets as a dietary supplement.


Caffeine is a mild stimulant used to temporarily relieve fatigue and increase mental alertness. Caffeine is added to some antihistamine drugs to help counteract the sleepiness they may cause. It is also added to over-the-counter headache remedies (e.g., Excedrin) and migraine headache drugs to enhance their painkilling effects. Some cold remedies contain caffeine for the same reason. Under medical supervision, citrated caffeine (a prescription drug) is used to treat breathing problems in premature infants.

Approximate amounts of caffeine in popular products


Amount of caffeine

Sprite, Fanta, 7 UP

12 oz (355 mL)

0 mg

Tea, decaffeinated

8 oz (240 mL)

1-4 mg

Coffee, decaffeinated, brewed

8 oz (240 mL)

2-12 mg

Hershey's Milk Chocolate

1.55 oz(43 g)

9 mg

Tea, green, brewed

8 oz (240 mL)

15 mg

Barq's Root Beer

12 oz (355 mL)

23 mg

Hershey's Special Dark Chocolate

1.45 oz (41 g)

31 mg

Coca-Cola Classic

12 oz (355 mL)

35 mg


12 oz (355 mL)

36-38 mg

Tea, black, brewed

8 oz (240 mL)

40-120 mg

Sunkist Orange, regular or diet

12 oz (355 mL)

41 mg

Dr Pepper

12 oz (355 mL)

42-44 mg

Diet Coke

12 oz (355 mL)

47 mg

Mountain Dew

12 oz (355 mL)

54 mg

Coffee, espresso

1 oz (30 mL)

58-75 mg

Excedrin® extra-strength headache

1 tablet

65 mg

Red Bull energy drink

8.3 oz (245 mL)

76 mg

SoBe No Fear energy drink

8 oz (240 mL)

83 mg

Coffee, brewed

8 oz (240 mL)

95-200 mg

5-hour ENERGY® drink

2 oz (59 mL)

138 mg

Monster Energy drink

16 oz (473 mL)

160 mg

NO-DOZ® maximum-strength caffeine

1 tablet

200 mg


Caffeine, from the Italian word caffè, meaning coffee, is naturally made by about 60 plants. The most familiar of these are coffee leaves and beans, tea leaves, kola nuts, yerba mate, guarana berries, and cacao (the source of chocolate). In plants, caffeine is a pesticide. Insects that eat plants containing caffeine become disabled or die.

Humans have eaten plants containing caffeine for thousands of years, first chewing the seeds and leaves, and later boiling them and drinking the resulting liquid. Coffee, a major source of caffeine, was introduced to Europe from the Middle East in the seventeenth century and rapidly became a popular drink. Coffee houses began appearing in London in the mid-1600s. A German chemist purified caffeine in 1819. In the twenty-first century, besides being found naturally in coffee, tea, and chocolate, caffeine is added to soft drinks, energy drinks and bars, headache remedies, and some cold and flu medications; it also is sold as a dietary supplement to improve mental and physical functioning.

Caffeine has no nutritional value, but it has these effects on the body:

It was formerly believed that caffeine acted as a diuretic, a substance that increases urine output. Research has since found that these effects are very mild, and that the diuretic effect is seen only when caffeine is consumed in large doses (.017–.021 oz. (500–600 mg), or up to 7 cups (1.7 L) of coffee per day). This means that moderate consumption of coffee and other caffeinated beverages does not cause dehydration.

Illustration of the main side effects of caffeine on the body: eyes (blurred vision), balance (dizziness), mouth (dryness), skin (red patches, paleness, cold sweats), heart (increase in cardiac rate), systemic (hyperglycemia),

Illustration of the main side effects of caffeine on the body: eyes (blurred vision), balance (dizziness), mouth (dryness), skin (red patches, paleness, cold sweats), heart (increase in cardiac rate), systemic (hyperglycemia), lungs (bad breath, difficulty in breathing), stomach (nausea, pain), intestines (diarrhea), central nervous system (drowsiness, anxiety, confusion, irritability, insomnia, decreasing or increasing hunger, thirst), muscles (shivering), and urinary system (increase in urination, increase of ketone in urine).
(JACOPIN/BSIP/Science Source)

Caffeine is on the U.S. Food and Drug Administration's (FDA) list of foods generally recognized as safe (GRAS). In moderate amounts, caffeine does not appear to be harmful to humans, although it is poisonous to dogs, horses, and some birds. Moderate generally means consumption in the range of.011–.014 oz. (300–400 mg) or 3–4 cups (.71–.95 L) of coffee daily. The Food Standards Agency in the United Kingdom recommends no more than 0.14 oz. (400 mg) per day for adults, but no limit has been set for healthy individuals. Anyone who experiences heart palpitations or sleeplessness should cut back. Caffeine has not been shown to cause birth defects and is considered safe in reasonable amounts during pregnancy. The March of Dimes Foundation and the Food Standards Agency recommend that pregnant women limit their caffeine intake to.01 oz. (200 mg) per day, roughly the amount in 12 oz. (.35 L) of coffee. Women experiencing difficulty sleeping may wish to completely eliminate caffeine from their diet.

By law, caffeine must be listed as an ingredient on food labels, but in the United States, the amount of caffeine per serving is not required to be disclosed. Because caffeine is added to so many products, it is difficult to measure the amount of caffeine in an individual's diet. The caffeine content of coffees and teas varies depending on where the plants were grown and how the beverages are prepared.

European Union Food Information Regulations require that food and drinks with high caffeine content be labeled to help consumers identify them and avoid caffeine if they so desire. Drinks with more than.005 oz. (150 mg) of caffeine per liter must state “High caffeine content. Not recommended for children or pregnant or breast-feeding women.” Foods to which caffeine has been added must contain a similar label.

BENEFITS: Although there is conflicting research, some studies have indicated benefits to regular caffeine consumption. A 2012 study published in the Journal of Alzheimer's Disease found that drinking roughly three cups of coffee per day over a lifetime could help prevent or delay the onset of Alzheimer's disease, particularly in the elderly. Other studies have linked similar amounts of caffeine consumption to improved memory and long-term cognition. A study of more than 50,000 women, published in the September 2011 issue of the Archives of Internal Medicine, found that women who drank at least four cups of coffee per day had a significantly lower rate (0.2%) of depression than women drinking fewer than one cup per week or even one cup per day (1.3% and 1.8%, respectively). Other benefits associated with moderate-to-high caffeine consumption include decreased risk of skin cancer (three cups per day), liver cancer (two cups a day, even decaffeinated), endometrial cancer (both regular and decaffeinated coffee, as well as pure caffeine), improved athletic performance (1–5 cups), and longer life expectancy (six cups). A study from 2017 found that caffeine can temporarily make food taste less sweet.

A 2017 study found that caffeine enhanced athletic performance most in individuals who did not regularly consume coffee or tea. The improvement is attributed to coffee's improvement of reaction times and the release of fat stores for energy. This effect is noticeable enough that Olympic officials once limited the amount of caffeine that athletes were allowed to consume before competition; this restriction was lifted in 2004.

Tea is also a source of caffeine, although most caffeinated teas have less caffeine per cup than coffee. Drinking tea is thought to confer a myriad of benefits, due to tea's antioxidant properties.


People vary in their sensitivity to caffeine based on their weight, age, personal biology, and habitual intake. Medications they are taking may also have an effect on an individual's caffeine sensitivity. People should be alert to how much caffeine they consume during a day and how it makes them feel, then adjust their intake accordingly. All of caffeine's effects are temporary, and withdrawal symptoms are likely to occur after a dose of caffeine wears off.

Caffeine stays in the system of pregnant women and people with liver damage longer than normal. These people should closely monitor their caffeine intake.

Caffeine passes into breast milk and, although it may have no effect on the breastfeeding woman, it may make the infant restless, irritable, and less likely to sleep. Recommendations for breastfeeding women vary from one to three cups of coffee per day, depending on the organization issuing the recommendation. If her infant seems to react to caffeine, a mother should reduce her intake.


Caffeine appears to enhance the effectiveness of over-the-counter headache and migraine remedies. Some of these medications contain a mixture of caffeine and painkillers. People with a high sensitivity to caffeine or those trying to reduce or monitor their intake (e.g., pregnant women) should read the labels carefully.


Although caffeine in moderate amounts poses no major health risks, the body quickly develops tolerance to the effects of caffeine, along with developing a mild physical and psychological dependency. For example, tolerance to caffeine-related sleep disruption disappears in about a week among people who drink three to four cups of coffee daily. The amount of caffeine it takes to reach this state is highly variable.

Discontinuing caffeine among regular users can cause withdrawal symptoms. These can include headaches (very common), irritability, nausea, fatigue, sleepiness, inability to concentrate, and mild depression. Caffeine withdrawal symptoms begin 12–24 hours after caffeine is stopped. Withdrawal symptoms peak at around 48 hours and can last up to five days. Tapering caffeine use, for example cutting down on caffeine by the equivalent of half a cup of coffee (about 50 mg) a day, minimizes or eliminates withdrawal symptoms.

People who consume more than.18 oz. (500 mg) of caffeine a day—equivalent to about five cups of coffee—may develop a condition called caffeinism, though the threshold varies among individuals. Caffeinism produces unpleasant sensations, some of which are similar to withdrawal symptoms. Symptoms of caffeine overuse include restlessness, irritability, nervousness, anxiety, muscle twitching, headaches, inability to fall asleep, and a racing heart. Severe overuse of caffeine can cause a number of related disorders, including:

An organic compound found in plants; chemically it is a base and usually contains at least one nitrogen atom.
Blood-brain barrier—
A specialized, semi-permeable layer of cells around the blood vessels in the brain that controls which substances can leave the circulatory system and enter the brain.
A condition in which the body either does not make or cannot respond to the hormone insulin. As a result, the body cannot use glucose (sugar).
A substance that removes water from the body by increasing urine production.
One of a group of chemicals secreted by a nerve cell (neuron) to carry a chemical message to another nerve cell, often as a way of transmitting a nerve impulse. Examples of neurotransmitters include acetylcholine, dopamine, serotonin, and norepinephrine.
Adjustment of the body to a drug so that it takes more and more doses to produce the same physiological or psychological effect, or adjustment to a drug so that side effects are diminished.

Parental concerns


Adolescents are increasingly using energy drinks and energy bars containing caffeine. In addition, adolescence is the time when many people start drinking coffee. Parents should educate their children about the effects of caffeine and encourage them to monitor their caffeine consumption from all sources. Concerns about children consuming caffeine in energy drinks became so strong that, in February 2018, several United Kingdom supermarket chains announced that they would no longer sell energy drinks to children under 16.

Accidental overdose from caffeine pills can be fatal. Caffeine tablets, like all drugs, should be kept out of reach of children. Children who accidentally eat caffeine pills need immediate medical attention.

See also Breastfeeding ; Cancer ; Dehydration .



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International Food Information Council Foundation, 1100 Connecticut Ave. NW, Ste. 430, Washington, DC, 20036, (202) 296-6540,, .

U.S. Food and Drug Administration (FDA), 10903 New Hampshire Ave., Silver Spring, MD, 20993, (888) 463 6332,, .

Tish Davidson, AM
Revised by Amy Hackney Blackwell, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.