Selective neuroendocrine effects of low-dose haloperidol in normal adult men

The neuroendocrine effects of haloperidol, usually reported as side effects of this drug when given in antipsychotic doses, have not been systematically investigated. In the present study five normal adult men were administered saline and two doses of of haloperidol (0.25 mg, 0.5 mg) intramuscularly in a double-blind randomized block design. The anterior pituitary hormones GH, LH, FSH, and PRL were measured in blood samples taken every 20 min for several hours thereafter. The low doses of haloperidol used have been shown by others to alter the human EEG; in our subjects these doses produced no objective or subjective clinical effects. There were no drug related changes in GH, LH, or FSH. PRL, however, showed a prompt, statistically significant, dose-related increase in plasma levels, with a return to baseline with 5 h. Haloperidol has strong dopamine-blocking effects, and the hypothalamic inhibitory mechanism for PRL release is believed to be dopamine-mediated. The results of this study suggest that haloperidol may have utility in low doses primarily for its hypothalamic neuroendocrine effects, and that dose-related PRL release may be a useful paradigm for comparing dopamine-blocking antipsychotic agents in humans.