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Caffeine is a drug that stimulates the central nervous system.


Caffeine makes people more alert, less drowsy, and improves coordination. Combined with certain pain relievers or medicines for treating migraine headache, caffeine makes those drugs work more quickly and effectively. Caffeine alone can also help relieve headaches. Antihistamines are sometimes combined with caffeine to counteract the drowsiness that those drugs cause. Caffeine is also sometimes used to treat other conditions, including breathing problems in newborns and in young babies after surgery.


Caffeine is found naturally in coffee, tea, and chocolate. Colas and some other soft drinks contain it. Caffeine also comes in tablet and capsule forms and can be bought without a prescription. Over-the-counter caffeine brands include No Doz, Overtime, Pep-Back, Quick-Pep, Caffedrine, and Vivarin. Some pain relievers, medicines for migraine headaches, and antihistamines also contain caffeine.

Recommended dosage

Adults and children age 12 years and over

100-200 mg no more than every 3-4 hours. In timed-release form, the dose is 200-250 mg once a day. Timed-release forms should not be taken less than six hours before bedtime.

Children under 12 years

Not recommended.

Other considerations

People should avoid taking much caffeine when it is being used as an over-the-counter drug and should consider how much caffeine is being taken in from coffee, tea, chocolate, soft drinks, and other foods that contain caffeine. A pharmacist or physician should be consulted to find out how much caffeine is safe to use.


Caffeine cannot replace sleep and should not be used regularly to stay awake as the drug can lead to more serious sleep disorders, such as insomnia.
People who use large amounts of caffeine over long periods build up a tolerance to it. When this happens, they have to use more and more caffeine to get the same effects. Heavy caffeine use can also lead to dependence. If the person then stops using caffeine abruptly, withdrawal symptoms may occur. These can include throbbing headaches, fatigue, drowsiness, yawning, irritability, restlessness, vomiting, or runny nose. These symptoms can go on for as long as a week if caffeine is avoided. Then the symptoms usually disappear. As of 2004, caffeine withdrawal has been officially recognized as a disorder classification manual.
If taken too close to bedtime, caffeine can interfere with sleep. Even if it does not prevent a person from falling asleep, it may disturb sleep during the night.
The notion that caffeine helps people sober up after drinking too much alcohol is a myth. In fact, using caffeine and alcohol together is not a good idea. The combination can lead to an upset stomach, nausea, and vomiting.
Older people may be more sensitive to caffeine and thus more likely to have certain side effects, such as irritability, nervousness, anxiety, and sleep problems.

Special conditions

Caffeine may cause problems for people with certain medical conditions or who are taking certain medicines.
ALLERGIES. Anyone with allergies to foods, dyes, preservatives, or to the compounds aminophylline, dyphylline, oxtriphylline, theobromine, or theophylline should check with a physician before using caffeine. Anyone who has ever had an unusual reaction to caffeine should also check with a physician before using it again.
PREGNANCY. Caffeine can pass from a pregnant woman's body into the developing fetus. Although there is no evidence that caffeine causes birth defects in people, it does cause such effects in laboratory animals given very large doses (equal to human doses of 12-24 cups of coffee a day). In humans, evidence exists that doses of more than 300 mg of caffeine a day (about the amount of caffeine in 2-3 cups of coffee) may cause miscarriage or problems with the baby's heart rhythm. Women who take more than 300 mg of caffeine a day during pregnancy are also more likely to have babies with low birth weights. Any woman who is pregnant or planning to become pregnant should check with her physician before using caffeine.
BREASTFEEDING. Caffeine passes into breast milk and can affect the nursing baby. Nursing babies whose mothers use 600 mg or more of caffeine a day may be irritable and have trouble sleeping. Women who are breastfeeding should check with their physicians before using caffeine.
OTHER MEDICAL CONDITIONS. Caffeine may cause problems for people with these medical conditions:
  • peptic ulcer
  • heart arrhythmias or palpitations
  • heart disease or recent heart attack (within a few weeks)
  • high blood pressure
  • liver disease
  • insomnia (trouble sleeping)
  • anxiety or panic attacks
  • agoraphobia (fear of being in open places)
  • premenstrual syndrome (PMS)
USE OF CERTAIN MEDICINES. Using caffeine with certain other drugs may interfere with the effects of the drugs or cause unwanted—and possibly serious—side effects.

Side effects

At recommended doses, caffeine can cause rest-lessness, 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. High caffeine consumption can lead to benign breast disease, which also can increase risk of breast cancer.


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 interferes with drugs that regulate heart rhythm, such as quinidine and propranolol (Inderal). 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.

Key terms

Arrhythmia — Abnormal heart rhythm.
Central nervous system — The brain and spinal cord.
Fetus — A developing baby inside the womb.
Palpitation — Rapid, forceful, throbbing, or fluttering heartbeat.
Withdrawal symptoms — A group of physical or mental symptoms that may occur when a person suddenly stops using a drug to which he or she has become dependent.
Serious side effects are possible when caffeine is combined with certain drugs. For example, taking caffeine with the decongestant phenylpropanolamine can raise blood pressure. And serious heart problems may occur if caffeine and monoamine oxidase inhibitors (MAO) are taken together. These drugs are used to treat Parkinson's disease, depression, and other psychiatric conditions. A pharmacist or physician should be consulted about which drugs can interact with caffeine.
Because caffeine stimulates the nervous system, anyone taking other central nervous system (CNS) stimulants should be careful about using caffeine. Those trying to withdraw from caffeine are advised to do reduce their consumption slowly over time by substituting decaffeinated or non-caffeinated products for some of the caffeinated products.



"Caffeine Withdrawal Recognized as Disorder." Ascribe Health News Service September 29, 2004.
"High Caffeine Intake May Increase Risk of Benign Breast Disease." Womenós Health Weekly September 16, 2004: 32.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


a purine compound found in most bodily tissues and fluids; it is a precursor of uric acid. Methylated xanthine compounds such as caffeine, theobromine, and theophylline are used for their bronchodilator effects.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


(kaf'ēn), Although this word was originally pronounced in three syllables, modern usage has fused the second and third syllables into one. Avoid the mispronunciation kaf-ēn'.
An alkaloid obtained from the dried leaves of Thea sinensis, tea, or the dried seeds of Coffea arabica, coffee; used as a central nervous system stimulant, diuretic, circulatory and respiratory stimulant.
Synonym(s): guaranine, thein
Farlex Partner Medical Dictionary © Farlex 2012




(kă-fēn′, kăf′ēn′)
A bitter white alkaloid, C8H10N4O2, found in certain plants such as cacao, coffee, kola, and tea, that stimulates the central nervous system and body metabolism and is used in medicine, usually in combination with other drugs, to relieve headaches and treat respiratory conditions in premature infants.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A methylxanthine that is the most widely used psychoactive substance on the planet.
Caffeine-bearing substances
Coffee, tea, maté, soft drinks, cocoa, Excedrin, NoDoz, colas, Red Bull, kola nuts, guarana products.

Low-dose (20–200 mg) effects
Positive subjective effects, feelings of well-being, alertness, energy.

High-dose effects
Nervousness, anxiety.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


Pharmacology A methylxanthine that is the most widely used psychoactive substance; it is present in coffee, tea, maté, soft drinks, cocoa, Excedrin, NoDoz, kola nuts, guarana products; low doses–20–200 mg produce positive subjective effects, feelings of well-being, alertness, energy; higher doses have adverse effects–eg, nervousness, anxiety. See Coffee.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


An alkaloid obtained from the dried leaves of Thea sinensis, tea, or the dried seeds of Coffea arabica, coffee; used as a central nervous system stimulant, diuretic, circulatory and respiratory stimulant, and adjunct in the treatment of headaches.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


One of the most popular and widely used drugs of mild addiction. Caffeine is used, in the form of coffee, tea and Cola-flavoured drinks, by about half the population of the world. It elevates mood, controls drowsiness, decreases fatigue and increases capacity for work. Caffeine is incorporated in various drug formulations such as Cafergot and Migril for the treatment of MIGRAINE.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


a bitter purine derivative found especially in coffee beans, tea leaves and cacao beans, and as an ingredient of soft drinks and aspirin tablets. It acts as a stimulant of the CENTRAL NERVOUS SYSTEM and as a DIURETIC. It is a BASE ANALOGUE and therefore likely to be a MUTAGEN.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


An alkaloid obtained from the dried leaves of Thea sinensis, tea, or the dried seeds of Coffea arabica, coffee; used as a central nervous system stimulant, diuretic, and circulatory and respiratory stimulant.
Medical Dictionary for the Dental Professions © Farlex 2012

Patient discussion about caffeine

Q. Am I addicted to caffeine? I love coffee! I can't start my day without it. I drink about 5 cups a day. How do I know if I am addicted?

A. When your body starts shaking, your heartbeat flutters, you feel lightheaded, you want to mow the lawn at 1 a.m., they are symptons I've had of a caffeine overdose. Drink lots of water and hydrating drinks! Stay away from Mountain Dew!!!!

Q. What is safer than caffeine but works just as well?

A. :? i fail to see what is so wrong with caffeine. as long as you don't over use it - it's fine. but if you insist of giving it up:
eat a light breakfast, orange juice.
at noon when you get tired- take a nap (less than 30 min. more than 15) after 2 weeks you won't understand how you lived without it.
exercise regularly, walk 40 min a day , 5 days a week.
that should do it.

Q. Whats the harm in drinking coffee? I drink coffee all day long and love it! My friends say I'm addicted and should cut back. But what is the harm in drinking coffee?

A. drinking coffee doesn't cause any significant damage, the only thing I can think of, is that when it is too much, coffe relax your exofagus esfinter, and stomach content could come out causing heartburn.

More discussions about caffeine
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References in periodicals archive ?
Having three or more servings of caffeinated beverages a day was associated with the onset of a migraine that day or the following day, according to the study published Aug.
A significant inverse association was found between caffeinated coffee intake and rosacea: Individuals who consumed four or more servings a day had a significantly lower risk of rosacea, compared with those who consumed one or fewer servings per month (hazard ratio, 0.77; 95% confidence interval, 0.69-0.87; P less than .001).
Similarly, the authority also launched a crackdown on caffeinated drinks as business adjustment time for these harmful beverages had also matured.
However, most concerning is the effect on sleep, the author explained a clear inverse association has been established between the consumption of caffeinated energy drinks and sleep duration.
The ban is part of a larger campaign to restrict high-calorie, low-nutrient foods, including fast food, sugary confectionary and highly caffeinated beverages.
However, drinking decaffeinated and caffeinated coffee, decaffeinated tea, iced tea, and soft drinks does not seem to make any difference to glaucoma risk, according to a study.
Boston, MA, September 21, 2017 --( Eat Your Coffee Bars: Caffeinated Energy Bars Packed with a Full Cup of Real Coffee
The research, conducted by YouGov and commissioned by Continental Tires as part of its Vision Zero safety initiative, reveals how drivers turn to different types of caffeinated drinks to help them maintain concentration, but warns of the dangers of relying on certain types of beverages to enhance levels of alertness.
Summary: Experts warn that caffeinated drinks can cause irritability, nervousness, muscle twitching, slurred speech
You are a different person when you are not properly caffeinated.
Consumption of caffeinated beverages among both women and men in the weeks before conception may increase the likelihood of a miscarriage, according to a study published in March in Fertility and Sterility.