potent synthetic tranquilizing drug that acts selectively upon the higher centres in the brain as a depressant of the central nervous system. It is used in the treatment of persons with psychotic disorders. Chlorpromazine was first synthesized in 1950 and became generally available for medical use in the mid-1950s. One of the first tranquilizers introduced into medicine—along with the rauwolfia alkaloid, reserpine—chlorpromazine soon displaced reserpine in psychiatric practice.

Chlorpromazine is a representative and important member of a series of tranquilizing agents that includes promazine, triflupromazine, and trifluoperazine; these agents are called phenothiazines (phenothiazine) because they are chemically related to the parasiticide phenothiazine.

Generally considered as the standard compound in the treatment of psychotic patients, chlorpromazine is widely used to suppress or mitigate delusions and hallucinations, to reduce agitation and violent behaviour, and to restore or increase the patient's response to psychotherapy. Some specific conditions treated with chlorpromazine are chronic delirium, manic states, conceptual disorders, motor hyperactivity, catatonia, and paranoia. A wide variety of schizophrenic conditions are alleviated by chlorpromazine.

The introduction of chlorpromazine and related drugs onto the wards of mental hospitals in the 1950s had profoundly beneficial medical and social effects. Many previously intractable, agitated, or grossly delusional patients became quieter, more rational, and more accessible to conventional psychotherapy. Such drugs enabled many episodically psychotic patients to have shorter stays in the hospital, and many other patients who would otherwise have been permanently institutionalized were able to live in the outside world once they were maintained on chlorpromazine.

The principal side effect of chlorpromazine is the rigidity it imparts to the muscles of certain patients; this rigidity may be accompanied by a characteristic tremor of the limbs involved. Chlorpromazine hydrochloride, sometimes marketed under the trade name Thorazine, may be administered orally or rectally or by injection.