Clinical investigations into antidepressive mechanisms. I. Antihistaminic and cholinolytic effects: amitriptyline versus promethazine.

It is assumed that established antidepressants exert their clinical efficacy by potentiation or decrease of central noradrenergic and serotonergic neurotransmission. However, recent experimental work suggests that antihistaminic and/or cholinolytic effects may also be involved. This double-blind controlled study compared amitriptyline (catecholamine potentiating, antihistaminic, cholinolytic) with promethazine (antihistaminic, cholinolytic) in 50 severely depressed inpatients over a 30-day treatment period. Analysis of the Hamilton depression rating scale revealed significant clinical superiority of amitriptyline over promethazine in such major depressive symptoms as depressed mood, suicidal ideation, psychic anxiety, and sleep disturbances. No significant difference was evident as far as autonomous side effects were concerned. Similar results were found by analysis of the AMP rating system. It is concluded that antihistaminic or cholinolytic effects per se do not explain the antidepressants' efficacy. However, potentiation of noradrenergic neurotransmission by cholinolytic activity might be the major antidepressive mechanism.