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Stimulants raise the general level of activity in the nervous system. The heart rate increases, nerve cells fire more easily, and a person reacts more quickly or intensely to challenging situations.

Just as heroin mimics the actions of the body's natural painkillers, stimulants mimic the function of the adrenal cortex in the brain that secretes adrenaline (epinephrine) into the bloodstream.


Amphetamine ("speed") was first synthesized in 1887, methamphet­amine in 1893. Neither was used as a drug until 1934. Then Smith, Kline and French started selling a form of amphetamine in an inhaler, used as a decongestant. They called it Benzedrine.

Amphetamines became widely known after World War II. During World War II, both sides used amphetamines. Japanese kamikaze pilots reportedly took amphetamines before their life-ending missions of attack on Allied warships. Hitler's doctor gave him methamphet­amine injections.

Allied spies were supplied with amphetamines when dropped behind enemy lines, in case they had to stay awake for days at a time to return to safety. Pilots in the U.S. Air Force are still supplied with amphetamines, a fact the government prefers not to discuss.

Amphetamines were widely abused in professional sports before being targeted by drug testing. Profes­sional baseball teams in the U.S. only started testing for amphet­amines in 2005, and hundreds of players tested positive for the drug.

What are the amphetamines?

In the 1960s dextroamphetamine (brand name Dexedrine) was the most commonly prescribed amphetamine. For many, the drug was synonymous with the term "diet pills."

During the mid to late 1960s a drug called "crystal" (crystallized meth­amphetamine) became popular in motorcycle clubs such as the Hell's Angels. Crystal meth was sometimes snorted (inhaled up the nose), but people who used it often ended up injecting it to get the maximum effect.

Because tolerance to amphet­amines built quickly, some users began to inject massive doses to maintain the effects. People would stay awake for days at a time, eating little if at all, engaged in nervous activity. After that they would "crash," sometimes sleep­ing for days.

So-called speed freaks could be identified on the streets of United States cities in the 1960s by their extremely thin arms and legs. Activated by the methamphet­amine for days at a time, but lacking appetite, they were digesting their own muscles.

What effects are produced by methamphetamine?

Methamphetamine returned in the 1990s as "ice." Ice was typically smoked rather than injected. By the late 1990s, there was an epidemic of methamphetamine production and addiction.

Methamphetamine abuse also spread well beyond the borders of the U.S. By 2000, methamphet­amine production was a major problem in Myanmar, and by 2007 it was reportedly a common drug of abuse throughout southeast Asia, where methamphetamine pills were used by workers to stay awake and work faster.

Amphetamines are interesting to psychologists not only as a public health problem but as a laboratory model for the effects of stress. Antelman, Eichler, Black, and Kocan (1980) showed that a dose of amphetamine was biochemically interchangeable with the effects of environmental stressors.

What did Antelman et al. discover about effects of amphetamine?

In non-human primates, amphet­amines were observed to cause a "staggering increase in aggres­sion." Sexual behavior may be similarly affected.

In humans, long-term admin­istration of amphetamines produces a syndrome indistin­guishable from paranoid schizophrenia, Symptoms include hallucinations of bugs crawling under the skin, plus para­noia and delusions of persecution.


Cocaine is said to be the most rein­forcing drug known, defined by the likelihood of users to take it repetitively. Methamphetamine may be equally or more reinforcing as defined by capture ratio (the likelihood of becoming addicted).

The effects of cocaine fade sooner than methamphetamine, so cocaine induces more repetitive drug-taking behavior. Rats will press a bar more times for a dose of cocaine than for any other drug.

Rhesus monkeys forced to choose between food and cocaine will choose cocaine almost exclusively. They lose weight and continue to binge until they die or the experiment is discontinued (Aigner & Balster, 1978).

Under what circumstances will monkey take cocaine until they die?

Why does cocaine have this effect? It acts directly on the dopaminergic (dopamine-using) areas of the midbrain. These areas are normally activated by biologically significant events.

Dopamine-using areas in the brain are activated by naturally pleasur­able experiences. These include religious ecstasy, pride over crea­tive accom­plishments, love, and sex.

Cocaine short-circuits the process. It brings the pleasure without the accomplishment. Instead of trying to repeat a biologically adaptive response, individuals repeatedly take cocaine.

Cocaine has a unique effect on the heart. It depresses activity in the vagus nerve, which normally slows the heart during the fight-or-flight response of the sympathetic nervous system.

Cocaine also acts as a general stimulant, raising the heart rate. The combination of these two effects can cause runaway cardiac activity during cocaine overdoses.

What unique combination of effects makes cocaine dangerous for the heart?

Cocaine is most pleasurable to people who are depressed or in pain. In this respect, it is like direct stimulation of the so-called pleasure centers of the limbic system.

Pleasure and pain normally act as an accelerator and a brake in the so-called hedonic control system of the body. This is the pleasure/pain motivational system.

Like all control systems, the hedonic control system seeks an equilibrium or an ideal state (homeostasis) by counteracting disturbances.(See the discussion of homeostasis at the beginning of Chapter 9: Motivation.)

Heavy use of cocaine, like heavy use of heroin or methamphet­amine, pushes the control system to an extreme in one direction. The control system pushes back. Anti-cocaine substances are secreted to break down the extra transmitters released by cocaine.

The same thing happens with heroin and most other psycho­active drugs: tolerance. A habitual user starts to require more of the drug, to achieve the same effect.

Just as addiction becomes more severe, the ability of a drug to produce joy comes to an end. A long-term addict is likely to needs the drug just to feel normal.

What is tolerance, in the context of drugs?

Some rebound effects occur quickly. Ecstasy users may report feeling "life is gray" after a weekend rave. Amphet­amine may produce excitement one day, a crash the next day. Crack users can report rebound effects in half an hour.

Drug withdrawal occurs as a drug gradually disappears from a person's system, after extended use. Withdrawal syndromes occur with all psychoactive drugs. They are different for each drug. An example is the headache some people experience if they do not have a morning cup of coffee.

What rebound reactions occur after drug use?



The most widely used stimulant drug is caffeine. Adults in the United States consume, on the average, over 10 pounds of coffee a year. That is a lot, considering 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. Some health benefits have been claimed. For example, people drinking several cups of coffee a day are statistically less likely to get Alzheimer's Disease.

Heavy coffee drinking (more than 4 or 5 cups a day, less if a person is not used to the drug) can lead to unpleasant sensations, sometimes called "jitters." Symptoms may include irregular heartbeats, anxiety, nervousness, and insomnia: the same effects produced by other stimulants and by adrenaline.

Grapefruit juice potentiates caffeine. Grapefruit juice inhibits an enzyme that normally removes caffeine from the blood. Combining grapefruit juice with coffee may give even a veteran coffee drinker the jitters.

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

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 discussing sleep, the chemical adenosine accumulates as a person remains awake. Adenosine inhibits the arousal-producing neurons of the brainstem, so adenosine makes us drowsy and inattentive when 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. Coffee interferes with the effect of adenosine and restores alertness.

What is caffeine's mechanism of action?

The response of individuals to caffeine varies. People who are prone to anxiety may show an exaggerated response to caffeine.

Charney, Heninger, and Jatlow (1985) found that people meeting the criteria for panic attacks and phobias responded more to caffeine. They were more likely to experience "anxiety, nervousness, fear, nausea, palpitations, restlessness, and tremors" compared to other people.

A person not accustomed to caffeine can react badly to a high dosage. Every year, caffeine pills send numerous college students to Emergency Rooms with panic attacks. Pills contain a concen­trated form of the drug, and that can have an exaggerated effect in people not accustomed to caffeine.

Why do caffeine pills sometimes result in hospital visits?

Like other psychoactive drugs, caffeine produces the phenomena of sensitization and tolerance (Meliska, Landrum, & Landrum, 1990). Sensitization occurs when caffeine is taken occasionally.

After sensitization, but before tolerance, a person becomes more reactive to a drug. With caffeine, a person who is sensitized may may experience sleeplessness after a single cup of coffee or other caffeinated beverage.

A person who drinks a lot of coffee may be able to have a cup before bedtime with little effect. This shows tolerance. The effect of caffeine is reduced.

Sudden withdrawal from caffeine produces headaches in some people. If such a person wants to stop drinking coffee, he or she must do so gradually.

What phenomena of sensitization and tolerance occur with caffeine?


Aigner, T. G. & Balster, R. L. (1978). Choice behavior in rhesus monkeys: Cocaine vs. food. Science, 201, 534-535.

Antelman, S. M., Eichler, A. J., Black, C. A., & Kocan, D. (1980). Interchangeability of stress and amphetamine in sensitization. Science, 207, 329-331.

Charney, D. S., Heninger, G. R., & Jatlow, P. I. (1985). Increased anxiogenic factors of caffeine in panic disorders. Archives of General Psychiatry, 42, 233-243.

Meliska, C. J., Landrum, R. E., & Landrum, T. A. (1990). Tolerance and sensitization to chronic and subchronic oral caffeine: Effects on wheelrunning in rats. Pharmacology Biochemistry & Behavior, 35, 477-479.

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