This is the 2007 version. Click here for the 2017 chapter 03 table of contents.


The most widely used stimulant drug is caffeine. Adults in the United States consume, on the average, over 10 pounds of coffee a year—a lot when you consider that many people drink no coffee at all. Coffee can be dangerous for a person with epilepsy or a heart condition, but researchers have found no dangers for normal healthy people.

What are dangers of too much coffee? What is the effect of combining grapefruit juice with coffee?

Heavy coffee drinking (more than 4 or 5 cups a day, less if a person is not used to the drug) can lead to irregular heartbeats, insomnia, and nervousness-the same effects produced by other stimulants and by adrenaline.

Oddly enough, grapefruit juice potentiates caffeine. Grapefruit juice inhibits an enzyme that normally removes caffeine from the blood; so combining grapefruit juice with coffee may give even a veteran coffee drinker the jitters. Sudden withdrawal from caffeine may produce headaches, so a coffee drinker who wishes to stop usually must taper off gradually.

Why do caffeine pills sometimes result in hospital visits?

The response of individuals to caffeine varies. For example, people who are prone to anxiety disorders often show an exaggerated response to caffeine. Charney, Heninger, and Jatlow (1985) found that people meeting the criteria for panic attacks and phobias (see p.551) responded to caffeine with more "anxiety, nervousness, fear, nausea, palpitations, restlessness, and tremors" compared to healthy subjects. Every year, caffeine pills send numerous college students to hospital Emergency Rooms with panic attacks. Pills contain a concentrated form of the drug that may have a powerful effect in people who are not used to it.

What is caffeine's mechanism of action?

In most people, caffeine produces a state of wakefulness and alertness. This may be related to basic regulation of the waking/sleeping cycle in the nervous system. As noted in the section on hypnotoxins earlier in this chapter, the chemical adenosine accumulates as a person remains awake. Adenosine inhibits the arousal-producing neurons of the brainstem, so adenosine may have a direct role in making us drowsy and inattentive when we are deprived of sleep. Caffeine has a molecular shape similar to adenosine and occupies the receptor sites on neurons where adenosine would normally have its effect, so coffee cuts the effect of adenosine and restores alertness.

What phenomena of sensitization and tolerance occur with caffeine?

Like other psychoactive drugs, caffeine produces the phenomena of sensitization and tolerance (Meliska, Landrum, & Landrum, 1990). Sensitization occurs when caffeine is taken occasionally. Then a person becomes more reactive to it. Tolerance occurs when caffeine is taken in regular, high doses. Then the effect of caffeine is reduced. As with other drugs, caffeine has its largest effect if it is used only occasionally or moderately. In a heavy user, it produces less effect. That is why a person who seldom drinks coffee may experience insomnia (sleeplessness) after having a cup of coffee at dinner hours before bedtime, while a person who drinks a lot of coffee may be able to have a cup before bedtime with little effect.

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