Caffeine-related disorders Health Article

Definition

Caffeine is a white, bitter crystalline alkaloid derived from coffee or tea. It belongs to a class of compounds called xanthines, its chemical formula being 1,3,7-trimethylxanthine. Caffeine is classified together with cocaine and amphetaminesas an analeptic, or central nervous system stimulant. Coffee is the most abundant source of caffeine, although caffeine is also found in tea, cocoa, and cola beverages as well as in over-the-counter and prescription medications for pain relief.

In the clinician's handbook for diagnosing mental disorders (the Diagnostic and Statistical Manual of Mental Disorders, known as the DSM-IV-TR), caffeine-related disorders are classified under the rubric of substance-related disorders. DSM-IV-TRspecifies four caffeine-related disorders: caffeine intoxication, caffeine-induced anxiety disorder, caffeine-induced sleep disorder, and caffeinerelated disorder not otherwise specified. A fifth, caffeine withdrawal, is listed under the heading of "Criteria Sets and Axes Provided for Further Study."

Caffeine-related disorders are often unrecognized for a number of reasons:

• Caffeine has a "low profile" as a drug of abuse. Consumption of drinks containing caffeine is unregulated by law and is nearly universal in the United States; one well-known textbook of pharmacology refers to caffeine as "the most widely used psychoactive drug in the world." In many countries, coffee is a social lubricant as well as a stimulant; the "coffee break" is a common office ritual, and many people find it difficult to imagine eating a meal in a fine restaurant without having coffee at some point during the meal. It is estimated that 10–12 billion pounds of coffee are consumed worldwide each year.
• People often underestimate the amount of caffeine they consume on a daily basis because they think of caffeine only in connection with coffee as a beverage. Tea, cocoa, and some types of soft drink, including root beer and orange soda as well as cola beverages, also contain significant amounts of caffeine. In one British case study, a teenager who was hospitalized with muscle weakness, nausea, vomiting, diarrhea, and weight loss was found to suffer from caffeine intoxication caused by drinking 8 liters (about 2 gallons) of cola on a daily basis for the previous two years. She had been consuming over a gram of caffeine per day. Chocolate bars and coffee-flavored yogurt or ice cream are additional sources of measurable amounts of caffeine.
• Caffeine has some legitimate medical uses in athletic training and in the relief of tension-type headaches. It is available in over-the-counter (OTC) preparations containing aspirin or acetaminophen for pain relief as well as in such OTC stimulants as NoDoz and Vivarin.
• Caffeine is less likely to produce the same degree of physical or psychological dependence as other drugs of abuse. Few coffee or tea drinkers report loss of control over caffeine intake, or significant difficulty in reducing or stopping consumption of beverages and food items containing caffeine.
• The symptoms of caffeine intoxication are easy to confuse with those of an anxiety disorder.

The DSM-TR-IVstates that it is unclear as of 2000 whether the tolerance, withdrawal symptoms, and "some aspects of dependence on caffeine" seen in some people who drink large amounts of coffee "are associated with clinically significant impairment that meets the criteria for Substance Abuse or Substance Dependence." On the other hand, a research team at Johns Hopkins regards caffeine as a model drug for understanding substance abuse and dependence. The team maintains that 9%–30% of caffeine consumers in the United States may be caffeine-dependent according to DSMcriteria for substance dependency.

Pharmacological aspects of caffeine

An outline of the effects of caffeine on the central nervous system (CNS) and other organ systems of the body may be helpful in understanding its potential for physical dependence. When a person drinks a beverage containing caffeine (or eats coffee-flavored ice cream), the caffeine is absorbed from the digestive tract without being broken down. It is rapidly distributed throughout the tissues of the body by means of the bloodstream. If a pregnant woman drinks a cup of coffee or tea, the caffeine in the drink will cross the placental barrier and enter the baby's bloodstream.

When the caffeine reaches the brain, it increases the secretion of norepinephrine, a neurotransmitter that is associated with the so-called fight or flight stressresponse. The rise in norepinephrine levels and the increased activity of the neurons, or nerve cells, in many other areas of the brain helps to explain why the symptoms of caffeine intoxication resemble the symptoms of a panic attack.

The effects of caffeine are thought to occur as a result of competitive antagonism at adenosine receptors. Adenosine is a water-soluble compound of adenine and ribose; it functions to modulate the activities of nerve cells and produces a mild sedative effect when it activates certain types of adenosine receptors. Caffeine competes with adenosine to bind at these receptors and counteracts the sedative effects of the adenosine. If the person stops drinking coffee, the adenosine has no competition for activating its usual receptors and may produce a sedative effect that is experienced as fatigueor drowsiness.