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THE MERCK MANUAL MEDICAL LIBRARY: The Merck Manual of Medical Information--Home Edition
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Among the drugs classified as amphetamines are amphetamineSome Trade Names
, methamphetamineSome Trade Names
(speed, crystal), and methylenedioxymethamphetamine (MDMA, Ecstasy, or Adam). MethamphetamineSome Trade Names
is the most commonly used amphetamineSome Trade Names
in the United States. Use of MDMA is growing in popularity. Amphetamines are usually taken by mouth but can be snorted, smoked, or injected.

Amphetamines may be used almost continuously or used intermittently. Some amphetamines are not approved for medical use, and some are manufactured and used illegally.

Some amphetamineSome Trade Names
abusers are depressed and seek the mood-elevating effects of these stimulants to temporarily relieve the depression. Others tend to use them in high energy activities, such as at dance parties. Amphetamines cause the release of increased amounts of dopamineSome Trade Names
in the brain, which is the likely cause of mood elevation. MDMA differs from the other amphetamines, in that it interferes with the reuptake of serotonin (one of the body's neurotransmitters) in the brain. AmphetamineSome Trade Names
users frequently develop dependence.

Symptoms and Complications

Amphetamines increase alertness (reduce fatigue), heighten concentration, decrease appetite, and enhance physical performance. They may induce a feeling of well-being, euphoria, and disinhibition.

In addition to stimulating the brain, amphetamines increase blood pressure and heart rate. Heart attacks have occurred, even in healthy young athletes. Blood pressure may become so high that a blood vessel in the brain ruptures, causing a stroke. Complications are more likely when drugs such as MDMA are used in warm rooms with little ventilation, when the user is very active physically (for example, dancing fast), or when the user sweats heavily and does not drink enough water to restore lost fluids.

People who habitually use amphetamines rapidly develop tolerance as part of their dependence. The amount used ultimately may exceed several hundred times the original dose. Most people using very high doses may become psychotic, because amphetamines can cause severe anxiety, paranoia, and a distorted sense of reality. Psychotic reactions include auditory and visual hallucinations (hearing and seeing things that are not there) and a feeling of having unlimited power (omnipotence). Although these effects can occur in any user, people with a mental health disorder, such as schizophrenia, are more vulnerable to them.

Symptoms opposite to the drug's effects occur when an amphetamineSome Trade Names
is suddenly discontinued. A person dependent on amphetamines becomes tired or sleepy—an effect that may last for 2 or 3 days after stopping the drug. Some people are severely anxious and restless, and some, especially those with a tendency toward depression, become depressed when they stop. They may become suicidal but may lack the energy to attempt suicide for several days.


Emergency treatment is needed only rarely. A person experiencing delusions and hallucinations may be given an antipsychotic drug, such as chlorpromazineSome Trade Names
, which has a calming effect and relieves distress. However, an antipsychotic drug may sharply lower blood pressure. Usually, reassurance and a quiet, nonthreatening environment help a person to recover.

Treatment may be needed to correct dehydration and other complications of use. Long-term users may need to be hospitalized during drug withdrawal for observance of suicidal behavior. Otherwise, no treatment is generally needed for people experiencing withdrawal.

Last full review/revision February 2003

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