Table of Contents


Caffeine is a mild alkaloid stimulant made by some plants. It is found in coffee beans, tea leaves, and cocao beans, added to soft drinks, energy drinks, energy bars, and sold in capsules and tablets as a dietary supplement. Caffeine has no nutritional value.


Caffeine is a mild stimulant. It is 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. Under medical supervision, citrated caffeine (a prescription drug) is used to treat breathing problems in premature infants.


Caffeine, from the Italian word cafée, 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 eating plants that contain caffeine become disabled or die.

Humans have eaten plants containing caffeine for thousands of years; first chewing the seeds and leaves,


ProductAmount of caffeine(mg)
Cocaine energy drink, 8.5 oz.280
Caffeine tablet, 1200
Coffee, brewed 8 oz.135
Red Bull energy drink, 8.5 oz.80
SoBe No Fear energy drink, 8 oz.80
Excedrin headache tablet, 165
Mountain Dew, 1 can, 12 oz.55
Black tea, brewed, 8 oz.50
Diet Coke, 1 can, 12 oz.45
Sunkist Orange, regular or diet, 1 can, 12 oz.41
Coffee, espresso, 1 oz.40
Pepsi Cola, 1 can, 12 oz.37
Coca-Cola Classic, 1 can, 12 oz.34
Hershey’s Special Dark chocolate, 1 bar, 1.5 oz.31
Barq’s Root Beer, 1 can, 12 oz.22
Green tea, brewed, 8 oz.15
Hershey’s Milk Chocolate, 1 bar, 1.5 oz.10
Coffee, decaffeinated, 8 oz.5
Tea, decaffeinated, 8 oz.4
Diet Barq’s Root Beer, 1 can, 12 oz.0
Sprite, diet or regular, 1 can, 12 oz.0
7-Up, 1 can, 12 oz.0

(Illustration by GGS Information Services/Thomson Gale.)

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. Today, besides being found naturally in coffee, tea, and chocolate, it is added to soft drinks, energy drinks and bars, headache remedies, and is sold as a dietary supplement to improve mental and physical functioning. The United States is a highly caffeinated nation. In 2007, it was estimated that 90% of North Americans consumed caffeine daily.

Caffeine is the most widely used psychoactive compound in the world. It has no nutritional value, but has these effects on the body:

  • increases heart rate
  • temporarily increases blood pressure
  • increases urine output (a diuretic)
  • relaxes smooth muscle cells in the airways
  • releases fatty acids and glycerol in the body for energy use
  • easily crosses the blood-brain barrier and changes the level of neurotransmitters in the brain
  • passes into breast milk

Many well-designed, well-documented studies show that caffeine makes people more alert, improves short-term memory, enhances the ability to concentrate, increases the individual’s capacity for physical work and speeds up reaction time. However, caffeine achieves this by preventing detrimental effects of withdrawal in habitual caffeine drinkers. It does not boost functioning to above normal levels. All these effects are temporary. Caffeine does not replace the need for rest or sleep.

Caffeine is on the United States Food and Drug Administration (FDA) list of foods generally recognized as safe (GRAS list). 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 rage of 300-400 mg or 3-4 cups of coffee daily. Caffeine has not been shown to cause birth defects and is considered safe in reasonable amounts during pregnancy. The March of Dimes Birth Defects Foundation recommends that pregnant women limit their caffeine intake to the equivalent of two cups of coffee per day, and that women who are having difficulty becoming pregnant eliminate caffeine from their diet.

By law, caffeine must be listed as an ingredient on food labels, but the amount of caffeine per serving is not required to be disclosed. Since caffeine is added to so many products, it is difficult to the amount of caffeine in an individual’s diet. Caffeine content of coffees and teas varies depending on where the plants were grown and how the beverages are prepared. The approximate amounts of caffeine is some common products are:

  • coffee, brewed 8 oz: 135 mg
  • coffee, decaffeinated, 8 oz: 5 mg
  • coffee, espresso, 1 oz: 40 mg
  • green tea, brewed, 8 oz: 15 mg
  • black tea, brewed, 8 oz: 50 mg
  • tea, decaffeinated, 8 oz: 4 mg
  • Mountain Dew, 1 can (12 oz): 55 mg
  • Coca-Cola Classic, 1 can (12 oz): 34 mg
  • Diet Coke: 1 can (12 oz) 45 mg
  • Pepsi Cola, 1 can (12 oz): 37 mg
  • Sunkist Orange, regular or diet, 1 can (12 oz): 41 mg
  • Barq’s Root Beer: 1 can (12 oz): 22 mg
  • diet Barq’s Root Beer: 1 can (12 oz): 0 mg
  • Sprite, diet or regular: 1 can (12 oz) 0 mg
  • 7-Up, 1 can (12 ounces): 0 mg
  • Red Bull energy drink, 8.5 oz: 80 mg
  • Cocaine energy drink, 8.5 oz: 280 mg
  • SoBe No Fear energy drink, 8 oz: 80 mg
  • Hershey’s Special Dark chocolate, 1 bar (1.5 oz): 31 mg
  • Hershey’s Milk Chocolate, 1 bar (1.5 oz): 10 mg
  • Excedrin headache tablet, 1: 65 mg
  • caffeine tablet, 1: 200 mg


People vary in their sensitivity to caffeine based on their weight, age, medications they may be taking, and personal biology. Individuals should be alert to how much caffeine they consume during a day and how it makes them feel, then moderate their intake accordingly. Caffeine does not replace the need for sleep. All mental and physical benefits are temporary and a “crash” is likely to occur after a dose of caffeine wears off. People who use caffeine to stay awake to drive or operate heavy machinery are at risk of being involved in an accident because of excessive tiredness once the effect 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.

Athletes should be aware that the International Olympic Committee tests for caffeine levels over 12 mg/ml of urine. This level could be reached by drinking four large cups of coffee.


Caffeine appears to enhance the effectiveness of over-the-counter headache remedies. Some of these medications contain a mixture of caffeine and painkiller. People with a high sensitivity to caffeine should read the labels carefully.

People taking diuretic medication (water pills) may see increased urine output because caffeine is a weak diuretic.


Discontinuing caffeine among regular users causes 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 use more than about 500 mg (the amount varies greatly among individuals) of caffeine a day may develop a condition called caffeinism. Caf-feinism produces unpleasant sensations, some of which are similar to withdrawal symptoms. Symptoms caffeine overuse include restlessness, irritability, nervousness, anxiety, muscle twitching, headaches, inability to fall asleep, and a racing heart. Severe overuse of caffeine can cause four psychiatric disorders recognized by the American Psychiatric Association and described in the Diagnostic and Statistical Manual of Mental Disorders, Fourth EditionCaffeine is considered the cause of these disorders after other causes have been ruled out.

  • Caffeine intoxication: Usually the result of taking caffeine pills (e.g., NoDoz), this condition causes mental changes, rambling thoughts and speech, irregular heart beat, and all symptoms associated with overuse. In severe cases death can result from ventricular fibrillation (unsynchronized contractions of the ventricle of the heart).
  • Caffeine-induced anxiety disorder: Severe anxiety that interferes with daily social interactions and occurs after caffeine intoxication or heavy long-term use of caffeine.
  • Caffeine-induced sleep disorder: An inability to sleep that is so great it requires medical/psychiatric attention and occurs after prolonged caffeine consumption.
  • Non-specific caffeine-induced disorder: Disorders not listed that are attributable to either acute or long-term caffeine consumption.

Parental concerns

Children get most of their caffeine from soft drinks. Parents should choose soft drinks that contain little or no caffeine or replace soft drinks with water,


Alkaloid—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.

Neurotransmitter—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 neuro-transmitters include acetylcholine, dopamine, serotonin, and norepinephrine.

Tolerance—Adjustment of the body to a drug so that it takes more and more to produce the same physiological or psychological effect, or adjustment to a drug so that side effects are diminished.

fruit juice, or low-fat milk. Adolescents are increasingly using energy drinks and energy bars containing caffeine. At the same time, many adolescents start drinking coffee. Parents educate their children about the effects of caffeine and encourage them to monitor their caffeine consumption from all sources.

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 from a physician or emergency room.


Klosterman, Lorrie. The Facts About Caffeine. New York:Marshall Cavendish Benchmark, 2006.

Mumaw, Stefan, and Wendy Lee Oldfield. Caffeine for the Creative Mind: 250 Exercises to Wake Up Your Brain. Cincinnati, OH: HOW Books, 2006.

Smith, Barry D., Uma Gupta, and B.S. Gupta, eds. Caffeine and Activation Theory: Effects on Health and Behavior. Boca Raton, FL: CRC Press, 2007.

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


American Heart Association. 7272 Greenville Avenue, Dallas, TX 75231. Telephone: (800) 242-8721. Website: <>.

Food Standards Agency, Aviation House. 125 Kingsway, London, UK WC2B 6NH Telephone: 020 7276 8000. Website: <>

International Food Information Council. 1100 Connecticut Avenue, NW Suite 430, Washington, DC 20036. Telephone: 202-296-6540. Fax: 202-296-6547. Website: <>.


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Doheny, Kathleen. “Pros and Cons of the Caffeine Craze.” October 17, 2006. [April 30, 2007]. <>

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March of Dimes Birth Defects Foundation. “Caffeine in Pregnancy.” 2007. [April 30, 2007]. <>.

Mayo Clinic Staff. “Caffeine Content of Common Beverages.” October 3, 2005. [cited April 30, 2007]. <>.

Mayo Clinic Staff. “The Caffeine Question: Should You Decaffeinate Your Diet?” March 8, 2007. [cited April 30, 2007]. <http://www.mayoclinic.-com/health/caffeine/NU00600>.

Tish Davidson, A.M.