Caffeine is a drug that stimulates the central nervous system. It makes people more alert, less drowsy, and improves coordination. When combined with certain pain relievers and 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 used to treat some breathing problems, because it widens the bronchial airways.

Caffeine was first discovered in coffee in 1820. It is also found naturally in tea and chocolate. Colas and some other soft drinks also contain it. Caffeine is sold in tablets and capsules that can be bought without a prescription.Over-the-counter caffeine brands include No Doz, Overtime, Pep-Back, Quick-Pep, Caffedrine, and Vivarin.

People who use large amounts of caffeine over long periods of time build up atolerance to it. When that happens, they have to use more and more caffeineto 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 aslong as a week if caffeine is avoided. Then the symptoms usually disappear.

Caffeine cannot replace sleep and should not be used regularly to stay awakeas the drug can lead to more serious sleep disorders, like insomnia. When determining caffeine dosage, be sure to consider how much caffeine is being taken in from coffee, tea, chocolate, soft drinks, and other foods. Check with apharmacist or physician to find out how much caffeine is safe to use.

Caffeine may cause problems for people with these medical conditions: food ordrug allergies, peptic ulcer, heart arrhythmias or palpitations, heart disease or recent heart attack, high blood pressure, liver disease, insomnia (trouble sleeping), anxiety or panic attacks, Agoraphobia (fear of being in open places), Premenstrual syndrome (PMS).

At recommended doses, caffeine can cause restlessness, 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 theeyes, 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.

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 tohuman doses of 12-24 cups of coffee a day). In humans, evidence exists thatdoses of more than 300 mg of caffeine a day (about the amount of caffeine in2-3 cups of coffee) may cause miscarriage or problems with the heart rhythm of the fetus. Women who take more than 300 mg of caffeine a day during pregnancy are also more likely to have babies with low birth weights.

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.

Serious side effects are possible when caffeine is combined with certain drugs. For example, taking caffeine with the decongestant phenylpropanolamine canraise blood pressure. And very serious heart problems may occur if caffeineand monoamine oxidase inhibitors (MAO) are taken together. Caffeine also interferes with drugs that regulate heart rhythm, such as quinidine and propranolol (Inderal). Because caffeine stimulates the nervous system, anyone taking other central nervous system (CNS) stimulants should be careful about using caffeine. Always check with a pharmacist or physician about which drugs can interact with caffeine.

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 may also interfere with the body's absorption of iron. Anyone who takes iron supplements should take themat least an hour before or two hours after using caffeine.

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