Effects of olanzapine and haloperidol on serum prolactin levels in male schizophrenic patients

It has been proposed that new atypical antipsychotics cause minimal prolactin (PRL) elevation compared to traditional antipsychotic agents because they spare dopamine blockade within the brain's tuberoinfundibular tract. The aim of this study was to compare the effects of olanzapine and haloperidol on PRL secretion in male schizophrenic patients. Twenty-nine male schizophrenic inpatients were included in the study. Fifteen of them were given olanzapine in a fixed dose of 10 mg/day PO and 14 of them were given haloperidol in a fixed dose of 10 mg/day PO for 6 weeks after a 2-week drug washout period. Fifteen age-matched healthy control subjects were used as control group. PRL levels were measured both before and after the 6-week treatment period in the patients. At the end of the 6th week, the PRL values observed with olanzapine treatment were significantly less than those observed with haloperidol, but not different from those of the controls. There was a significant positive correlation between the PRL values and the severity of extrapyramidal side effects in only the haloperidol group after the six week's treatment period. Our data indicate that short-term olanzapine treatment at doses of 10 mg/day PO causes minimal elevations in PRL secretion in male schizophrenic patients in contrast to haloperidol. This finding is consistent with the previous reports and may be attributed to olanzapine's differential effects on dopamine neurotransmission.