The relationship between neuroleptic dosage and cognitive functioning in chronic schizophrenic patients

A review of the effects of phenothiazines on cognitive function suggests that phenothiazine derivatives facilitate performance on tests of cognitive function, at least in subjects who are thought disordered. Drug effects frequently depend on the dose administered, however, and the response to various doses of some drugs (e.g., antidepressants) is frequently nonlinear. In our study, 23 hospitalized males with chronic psychotic disorders, and stabilized on dosages of neuroleptics with chlorpromazine equivalents of from 50 to 7,200 milligrams daily, were tested in the morning and in the evening of the same day with the Mini-Mental State examination [1]. Cognitive functioning was positively correlated (+0.49) with dosage, but the relationship was curvilinear. Functioning improved with increasing dose up to a dose of about 2,000 milligrams daily; beyond that dosage (and up to 7,200 milligrams daily) functioning plateaued. Scores on same-day retest were essentially unchanged regardless of dose. The implication of these findings for the management of chronic psychotic patients is discussed.