Moclobemide effects on prolactin plasma levels in healthy individuals: the hormonal increase induced by a single dose is maintained during a 4-week period of drug intake.

Neuroendocrine challenge studies are frequently used to study the pathophysiology of psychiatric illnesses and the effects of psychotropic drug treatment on brain monoamine function. Moclobemide, a reversible inhibitor of monoamine oxidase, with predominant effects on the A-type of the enzyme, was administered to 15 healthy men. Seven out of the 15 also received single blind placebo a week before the moclobemide. The individuals received moclobemide as a single dose (150 mg), followed by doses of 150 mg three times a day, during a 4-week period. Plasma prolactin was measured in the morning over a 150-min period, following the single dose, and then at the end of weeks 1, 2 and 4 of moclobemide intake. The present data show an acute and transitory increase of plasma prolactin levels after the single dose, and also during the long-term moclobemide administration. It might indicate that steady-state moclobemide levels, during the long-term drug administration, were low and thus large fluctuations of drug levels occurred between doses. Thus, it is suggested that larger doses or administering smaller doses more frequently, or both, may induce hyperprolactinaemia with clinical consequences.