the first drug of the monoamine-oxidase inhibitor series to be introduced into medicine (1958). It was employed as an antidepressant until it was found to cause liver damage. Prior to its introduction as an antidepressant, iproniazid was studied as a drug similar in function to the antituberculotic drug isoniazid, which it resembles in chemical structure. It prevents the enzymatic breakdown of norepinephrine, the brain-neurotransmitter substance concerned with emotional stimulation. It does so by inhibiting the enzyme monoamine oxidase.

Iproniazid has been replaced in antidepressant therapy by other members of the monoamine-oxidase inhibitor series (e.g., isocarboxazid, phenelzine, and tranylcypromine) and the tricyclic antidepressant drugs (e.g., imipramine, amitriptyline, and nortriptyline), which have less severe side effects.