YOHIMBINE IS AN INDOLALKYLAMINE ALKALOID WITH CHEMICAL SIMILARITY TO RESERPINE. IT BLOCKS PRESYNAPTIC ALPHA-2 ADRENERGIC RECEPTORS. ITS ACTION ON PERIPHERAL BLOOD VESSELS RESEMBLES THAT OF RESERPINE, THOUGH IT IS WEAKER AND OF SHORTER DURATION. YOHIMBINE'S PERIPHERAL AUTONOMIC NERVOUS SYSTEM EFFECT IS TO INCREASE PARASYMPATHETIC (CHOLINERGIC) AND DECREASE SYMPATHETIC (ADRENERGIC) ACTIVITY. IT IS TO BE NOTED THAT IN MALE SEXUAL PERFORMANCE, ERECTION IS LINKED TO CHOLINERGIC ACTIVITY AND TO ALPHA-2 ADRENERGIC BLOCKADE WHICH MAY THEORETICALLY RESULT IN INCREASED PENILE INFLOW, DECREASED PENILE OUTFLOW OR BOTH.
YOHIMBINE HAS A MILD ANTI-DIURETIC ACTION, PROBABLY VIA STIMULATION OF HYPOTHALAMIC CENTERS AND RELEASE OF POSTERIOR PITUITARY HORMONE.