Approximate amounts of caffeine in popular products
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Caffeine-related disorders are a group of psychiatric disorders defined by DSM-5 * that are caused by taking in large amounts of caffeine in foods, drinks, or over-the-counter medications. Caffeine is a stimulant * that also affects the muscles and the digestive tract. Some doctors include digestive problems caused by caffeine in the category of caffeine-related disorders.
Keith, a high school student in Chicago, got into the habit of drinking Redline, a caffeinated energy drink that his friends recommended as a way of boosting his energy and endurance before basketball practice. Keith thought of Redline as much like a soft drink: a drink to quench thirst as well as to improve sports performance. Before long he was drinking two or three cans per day.
One afternoon Keith felt sick after his basketball game. He could feel his heart beating, he was sweating heavily, and he could not stop vomiting. He was also very anxious. The coach took him to the emergency room of a nearby hospital, where the doctor diagnosed Keith with caffeine intoxication. Keith was surprised to learn how much caffeine he had been taking on a daily basis and how quickly it could affect his health.
Caffeine is a naturally occurring chemical compound that is classified as a xanthine (ZAN-theen). Xanthines are nitrogen-based compounds that are found in both plant and animal tissue and have a stimulating effect on the nervous system. Caffeine itself is found in various amounts in the stems, leaves, and berries or beans of some plants, particularly the coffee plant and the leaves of tea bushes. Other natural sources of caffeine used by humans to make beverages include yerba maté, a shrub in the holly family that grows in South America; guarana, a climbing plant found in the Amazon rain forest; kola nuts, used to flavor cola beverages; and cacao pods, the source of cocoa and chocolate. The caffeine in all these plants acts as a natural pesticide that paralyzes and kills insects that would otherwise feed on their leaves and berries.
Caffeine is the most widely consumed psychoactive * substance in the world, although most people do not think of it as a drug. Unlike most other psychoactive substances, caffeine is legal and unregulated in almost all countries. The U.S. Food and Drug Administration (FDA) first defined caffeine as a “multiple purpose generally recognized as safe food substance.” Now, the FDA describes caffeine as being “both a drug and a food additive.” This change in wording reflects a growing awareness around the world that caffeine can be addictive when it is overused and that it can have toxic side effects in people who take very high doses of it or who are unusually sensitive to its effects.
Humans have known for centuries about the effects of caffeine in improving alertness, fighting off drowsiness, and increasing physical endurance and muscular coordination. There is evidence from Stone Age burial sites that early humans (possibly as early as 10,000 BcE) knew that chewing the leaves of plants containing caffeine relieved fatigue, enabled people to do hard physical work for longer periods of time, and helped to lift depressed moods. It was not until about 3000 BcE that the Chinese discovered that soaking tea leaves in hot water produced a beverage containing more caffeine than the fresh tea leaves themselves. Brewed coffee appeared in the Arab world around the 9th century CE but did not reach Europe until the 17th century.
Cacao beans were used for their caffeine content by the Maya in southern Mexico as early as 600 BCE. The cacao beans were ground and flavored with vanilla and chili peppers to make a spicy drink to relieve tiredness. When the Spanish conquistadors came to Mexico in the 16th century CE, they adopted the chocolate-flavored drink (minus the chili peppers), and brought it back to Europe. They planted cacao trees in the West Indies and the Philippines to supply the new European craving for chocolate.
In the 20th century, kola nuts were used by the Coca-Cola Company to flavor its well-known soft drink. Although most cola-flavored soft drinks use artificial flavoring, some energy drinks use kola nuts as well as guarana berries to increase their caffeine content.
Caffeine is classified as a central nervous system * stimulant because it reduces drowsiness and increases alertness and the ability to focus. It is also a diuretic * , which means that it increases the loss of body water in the urine.
Caffeine usually enters the body through the mouth and is absorbed by the stomach and small intestine within 45 minutes. The half-life of caffeine—that is, the time it takes for the body to eliminate half the caffeine taken at one time—varies according to age, sex, the healthiness of a person's liver, and other medications the person may be taking. In general, the half-life of caffeine in a healthy adult is three to four hours. In pregnant women, the half-life of caffeine is 9 to 11 hours; in young children, it is as long as 30 hours; and in elderly adults with liver disease, it can be as long as 96 hours.
After being absorbed from the digestive tract, caffeine passes rapidly into other body tissues. It can affect the brain because it is able to cross the blood-brain barrier * . Once in the brain, caffeine acts primarily as an antagonist * of a brain chemical called adenosine (ah-DEN-oh-seen), a chemical that occurs naturally in the body and among its other functions promotes sleep and suppresses arousal. It is also involved in the sleep-wake cycle. Caffeine's ability to increase alertness and physical endurance is largely due to its role as an adenosine antagonist.
In the digestive tract, caffeine stimulates the stomach to produce more gastric acid and reduces muscle tone in the (lower esophageal) esophago-gastric sphincter (the muscle ring that closes off the esophagus from the stomach during digestion), which is the reason why some people experience heartburn after drinking tea or coffee. Caffeine is metabolized (broken down) in the liver into three simpler compounds. One of these compounds is a diuretic; it increases the person's urine output. This pattern of caffeine metabolism *
Other effects of caffeine on the digestive tract include stimulation of the gallbladder * and the colon * . In addition, caffeine relaxes the muscles of the anal * sphincter (SFINK-ter), the ring of muscles surrounding the anus that holds fecal matter inside the body. The effects of caffeine on the colon and anal sphincter help to explain why people with fecal incontinence * should not drink coffee or tea.
People who drink large quantities of coffee, tea, or energy drinks develop a tolerance to the psychological and physical effects of caffeine. This means that people get used to the stimulant effects of caffeine and are not kept awake at night even after consuming several cups of tea or coffee. Tolerance to caffeine builds up quite rapidly; one study found that test subjects who took 400 mg of caffeine three times per day for seven days did not have any problems with sleep. Another study found that subjects who took in 300 mg of caffeine three times per day for 18 days developed complete tolerance to the psychological effects of caffeine.
The other side of caffeine tolerance is caffeine withdrawal * . Withdrawal refers to the symptoms experienced by heavy caffeine users when they suddenly stop taking large amounts of caffeine. The most common symptoms of caffeine withdrawal are headache, nausea, drowsiness or difficulty sleeping, irritability, difficulty concentrating, and pain in the stomach, upper body, or joints. Some people may experience psychological depression. Caffeine withdrawal begins within 12 to 24 hours after the last dose of caffeine and lasts anywhere from one to five days.
Although most people think of caffeine simply as an ingredient in certain foods and beverages it is used in some medications to improve the effectiveness of aspirin and other pain relievers, to treat migraine headaches, or to counteract the drowsiness caused by antihistamines * . A number of over-the-counter medications taken to relieve menstrual cramps or to help dieters control their appetite contain caffeine.
Caffeine-related disorders are a group of four mental disorders defined by DSM-5. Some doctors also use the term loosely to refer to physical problems caused or made worse by consuming large amounts of caffeine.
DSM-5 defines four caffeine-related psychiatric disorders:
The long-term use of high doses of caffeine has been linked to several digestive problems caused by increased secretion of stomach acid:
There is less agreement among doctors about the effects of high doses of caffeine on miscarriage * . Some studies maintain that high caffeine intake doubles a woman's risk of miscarriage, whereas several other studies found no connection. In addition, while children can experience the same symptoms of anxiety, increased heart rate, and digestive disturbances as adults, there is no evidence that caffeine stunts children's growth.
In addition, the caffeine content of coffee or tea can vary from cup to cup, depending on the growing conditions at the time the coffee or tea was produced, the processing techniques that were used before the coffee or tea was marketed, and the method of preparation used. Even beans from the same coffee bush in the same growing season can show variations in caffeine content. One 5-ounce serving of coffee can range from 40 to 100 mg of caffeine per cup.
Another reason why it is difficult to gather accurate statistics about the frequency of caffeine-related disorders is that many people who are dependent on caffeine are also taking other psychoactive drugs. Using caffeine along with alcohol or other drugs makes it hard to tell how much the caffeine by itself contributes to the patient's symptoms. In addition, about 50 percent of people diagnosed with depression and other mood disorders * are dependent on caffeine. This overlap with other mental disorders makes it hard to tell how many people in the general population have caffeine-related disorders. DSM-5 states simply that the frequency of caffeine-related disorders is unknown.
People commonly experience one or more symptoms of a caffeine-related disorder if they consume large quantities of caffeine on a daily basis. They may not always draw a connection between their symptoms and caffeine. One reason is that people vary in their sensitivity to caffeine. Another reason is that people do not always add up all the caffeine they take in from different sources in a short period of time. Individuals who drink a cup of coffee with each meal, take a caffeinated headache remedy, and drink a lot of cola may consume much more caffeine than they realize. Common symptoms of high caffeine intake include:
Some people do not recognize that they may have a caffeine-related disorder until they try to stop drinking caffeinated beverages or using caffeinated over-the-counter medications. Researchers at Johns Hopkins University found that some people can experience the symptoms of caffeine withdrawal when they are used to doses of caffeine as low as 100 mg per day, which is the caffeine equivalent of one 6-ounce cup of brewed coffee or two to three 12-ounce servings of caffeinated soft drink.
Most people who experience the symptoms of caffeine withdrawal or caffeine jitters do not suffer any long-term consequences. The most serious consequences of caffeine-related disorders are found in individuals who combine caffeine with alcohol or other drugs and then drive under the influence or engage in other risky behaviors. One study of college students who were heavy drinkers of alcohol combined with energy drinks reported that these students had much higher than average rates of car accidents, being injured while riding with an intoxicated driver, date rape, and falls or other accidents that needed a doctor's attention.
The diagnosis of caffeine-related disorders begins with taking a careful patient history, including any other substances the patient may be using and other mental disorders being treated as well as the patient's use of caffeine. The reason for asking about other substance use (or abuse) and treatment for other psychiatric conditions is that the symptoms of caffeine-related disorders can be disguised by the symptoms of other substance abuse and mental disorders. Caffeine can also worsen the symptoms of depression, anxiety, and panic attacks * .
To narrow the diagnostic possibilities, the doctor may perform a mental status examination (MSE) in the office. This is a brief test in which the patient is asked to answer a set of questions, follow simple instructions, and walk across the room while the doctor evaluates the patient's appearance, mood, speech patterns, coordination, thought processes, insight, judgment, and perceptions. A person with a caffeine-related disorder will often appear jittery, tense, having trouble making eye contact, and generally fidgety. The person would not have hallucinations or memory problems, be disoriented, or talk about suicide or murder simply from the effects of caffeine. Any person with these symptoms has another mental or substance abuse disorder.
Caffeine can be detected in the blood, but blood tests are not useful in diagnosing caffeine-related disorders. The doctor might order a urine test to rule out other drug-related disorders or an electrocardiogram * to evaluate an irregular heartbeat if one is present.
Treatment of caffeine-related disorders consists of lowering daily caffeine consumption or stopping it altogether. Withdrawal symptoms can be treated by taking pain relievers containing small amounts of caffeine until the withdrawal is over.
Caffeine-related disorders can be prevented by becoming knowledgeable about the caffeine content of favorite foods or over-the-counter medications and monitoring one's daily intake of caffeine. One can also prevent caffeine-related disorders by simply avoiding all products with significant amounts of caffeine. Some religious groups, such as the Mormons, Seventh-day Adventists, and some sects of Hinduism discourage their members from drinking caffeinated beverages.
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American Psychiatric Association. 1000 Wilson Blvd., Suite 1825, Arlington, VA 22209. Telephone: 703-907-7300. Website: http://www.psychiatry.org (accessed March 5, 2016).
U.S. Food and Drug Administration. 10903 New Hampshire Ave., Silver Spring, MD 20993. Toll-free: 888-463-6332. Website: http://www.fda.gov (accessed March 5, 2016).
* DSM-5 is The Diagnostic and Statistical Manual of Mental Disorders, 5th revision, published by the American Psychiatric Association. This is the system of classification and diagnosis of mental conditions used in the United States.
* stimulant (STIM-yoo-lunt) is a drug that produces a temporary feeling of alertness, energy, and euphoria.
* psychoactive (sy-ko-AK-tiv) means affecting a person's mood, behavior, perceptions, or consciousness.
* central nervous system (SEN-trul NER-vus SIS-tem) is the part of the nervous system that includes the brain and spinal cord.
* diuretics (dye-yoor-EH-tiks) are medications that increase the body's output of urine.
* blood-brain barrier is a biological shield in the body that helps prevent germs or other potentially harmful materials in the blood from entering the brain and spinal cord.
* antagonist (an-TAG-oh-nist) is a chemical that acts within the body to reduce or oppose the effects of another chemical.
* metabolism (meh-TAB-o-liz-um) is the process in the body that converts food into the energy necessary for body functions.
* gallbladder is a small pearshaped organ on the right side of the abdomen that stores bile, a liquid that helps the body digest fat.
* colon (KO-lin), also called the large intestine, is a muscular tube through which food passes as it is digested, just before it moves into the rectum and out of the body through the anus.
* anal refers to the anus, the opening at the end of the digestive system through which waste leaves the body.
* incontinence (in-KON-ti-nens) is loss of control of urination or bowel movement.
* withdrawal is a group of symptoms that occurs when a drug that causes physical or psychological dependence is regularly used for a long time and then suddenly discontinued or decreased in dosage.
* antihistamines (an-tie-HIS-tuhmeens) are drugs used to combat allergic reactions and relieve itching.
* insomnia is an abnormal inability to get adequate sleep.
* esophagus (eh-SAH-fuh-gus) is the soft tube that, with swallowing, carries food from the throat to the stomach.
* miscarriage (MIS-kare-ij) is the end of a pregnancy through the death of the embryo or fetus before birth.
* mood disorders are mental disorders that involve a disturbance in the person's internal emotional state. They include depressive disorders, bipolar disorders, and mood disorders associated with the use of drugs or medical illnesses.
* palpitation is the sensation of a rapid or irregular heartbeat.
* panic attacks are periods of intense fear or discomfort with a feeling of doom and a desire to escape. During a panic attack, a person may shake, sweat, be short of breath, and experience chest pain.
* electrocardiogram (e-lek-troKAR-dee-o-gram), also known as an ECG, is a test that records and displays the electrical activity of the heart.