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Alternative Titles: tranquiliser, tranquillizer

Tranquilizer, also spelled Tranquillizer, drug that is used to reduce anxiety, fear, tension, agitation, and related states of mental disturbance. Tranquilizers fall into two main classes, major and minor. Major tranquilizers, which are also known as antipsychotic agents, or neuroleptics, are so called because they are used to treat major states of mental disturbance in schizophrenics and other psychotic patients. By contrast, minor tranquilizers, which are also known as antianxiety agents, or anxiolytics, are used to treat milder states of anxiety and tension in healthy individuals or people with less serious mental disorders. The major and minor tranquilizers bear only a superficial resemblance to each other, and the trend has been to drop the use of the word tranquilizer altogether in reference to such drugs, though the term persists in popular usage.

  • Chlordiazepoxide (Librium) produces a calming effect and is used to reduce the physical and …
    U.S. Drug Enforcement Administration

Major tranquilizers are highly selective in alleviating the delusions, hallucinations, and disordered thinking of schizophrenics and other psychotic patients. The drugs return agitated, excited, and irrational patients to a state of rational calm, and they have enabled many seriously ill people who would otherwise be hospitalized to live at home and engage in productive work. Major tranquilizers do not cure schizophrenia but merely suppress its symptoms, and they are usually prescribed on a long-term basis. The basic types are the phenothiazines, thioxanthines, butyrophenones, clozapine, and rauwolfia alkaloids. The phenothiazines are the most widely used of these and include the drug chlorpromazine. They are thought to work by blocking the neurotransmitter dopamine in the brain. This leads to a reduction of psychotic symptoms but can also result in such unwanted side effects as tremors of the limbs, rigidity, restlessness, and involuntary spasms of the facial muscles, tongue, and lips. (See also phenothiazine.) The thioxanthines and the butyrophenones, chief among which is haloperidol (Haldol), are similar to the phenothiazines. Another drug, clozapine, whose exact mode of action remains unclear relieves schizophrenic symptoms in some patients who are not helped by phenothiazines. Clozapine lacks the side effects of the phenothiazines but tends to induce an infectious disease known as agranulocytosis. The rauwolfia alkaloids, such as reserpine, are no longer in common use.

The principal minor tranquilizers are the benzodiazepines, among which are diazepam (Valium), chlordiazepoxide (Librium), and alprazolam (Xanax). These drugs have a calming effect and eliminate both the physical and psychological effects of anxiety or fear. Besides the treatment of anxiety disorders, they are widely used to relieve the strain and worry arising from stressful circumstances in daily life. Because of this, benzodiazepines are among the most widely prescribed drugs in the world. Benzodiazepines work by enhancing the action of the neurotransmitter gamma-aminobutyric acid (GABA), which inhibits anxiety by reducing certain nerve-impulse transmissions within the brain. Benzodiazepines resemble barbiturates in their side effects: sleepiness, drowsiness, reduced alertness, and unsteadiness of gait. Though less dangerous than barbiturates, they can produce physical dependency even in moderate dosages, and the body develops a tolerance to them, necessitating the use of progressively larger doses. The drugs are thus intended for short- and medium-term use. Other, less commonly used minor tranquilizers include meprobamate (Equanil, Miltown) and buspirone (BuSpar).

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widely used anthelmintic (worming agent) in veterinary medicine. Phenothiazine is an organic compound effective against a broad range of parasites in cattle, horses, poultry, sheep, and swine. A highly toxic drug, it is not recommended for human use and is not effective in dogs or cats.

in drug use

A piece of compressed cocaine powder.
There are many sanctioned uses for drugs that exert an effect on the central nervous system. Consequently, there are several classes of nonnarcotic drugs that have come into extensive use as sleeping aids, sedatives, hypnotics, energizers, mood elevators, stimulants, and tranquilizers.
Serendipity has played a major role in the discovery of tranquilizers (as it has in all facets of medicine). Tranquilizers were unknown to medical science until the middle of the 20th century, when the therapeutic value of reserpine and chlorpromazine in psychiatry was discovered by chance. Reserpine was originally derived in the 1930s from Rauwolfia serpentina, a woody plant that grows...
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