Effect of clozapine on human serum prolactin levels

The authors determined serum prolactin levels in 13 patients receiving clozapine, an antipsychotic drug that does not produce extrapyramidal side effects. Morning serum prolactin levels, 11 hours after the last dose, were not elevated during chronic treatment with clozapine in any subject despite its therapeutic effects. Serum prolactin levels were moderately increased between 90 minutes and 4 hours after administration of very high doses of oral clozapine in 4 patients but were smaller than those produced by chlorpromazine in other subjects. The authors suggest that clozapine may achieve its antipsychotic effect differently than do classical neuroleptics and that sustained prolactin increases are not essential for antipsychotic action.