Oral contraceptives increase the plasma concentrations of chlorpromazine.

A 21-year-old female inpatient who was enrolled in a population pharmacokinetic study of chlorpromazine was given an oral chlorpromazine dose of 100 mg three times daily, and plasma concentrations of chlorpromazine were measured weekly. This dose was well tolerated during the first week of therapy. In the second week the patient took a combined oral contraceptive; this was followed by severe dyskinesias and tremor. Plasma chlorpromazine levels were found to be about sixfold higher than those in the first week, although the dose of chlorpromazine had not changed. This observation suggests that the oral contraceptive increased the plasma concentration of chlorpromazine.