QUINAGOLIDE, THE ACTIVE INGREDIENT OF NORPROLAC, IS A SELECTIVE DOPAMINE D2-RECEPTOR AGONIST NOT BELONGING TO THE CHEMICAL CLASSES OF ERGOT OR ERGOLINE COMPOUNDS. OWING TO ITS DOPAMINERGIC ACTION, THE DRUG EXERTS A STRONG INHIBITORY EFFECT ON THE SECRETION OF THE ANTERIOR PITUITARY HORMONE PROLACTIN, BUT DOES NOT REDUCE NORMAL LEVELS OF OTHER PITUITARY HORMONES.