Comparison of haloperidol and chlorpromazine in the treatment of phencyclidine psychosis.

Phencyclidine (PCP) is a widely abused drug inducing a psychosis relieved by such dopamine antagonists as the neuroleptics. In the current study we compared two neuroleptics which act at different dopamine receptor sites. Haloperidol, a DA-2 receptor antagonist, and chlorpromazine, a DA-1 antagonist, were used to treat a total of 20 patients who experienced a phencyclidine psychosis. Ten patients each received two doses of one or the other neuroleptic on an alternating basis. Haloperidol 5 mg i.m. was shown to be superior to chlorpromazine 50 mg i.m. in relieving all signs of psychosis. The authors hypothesize that the DA-2 receptor is site-specific for PCP.