A hydrazine derivative and a potent non-selective monoamine oxidase (MAO) inhibitor with anxiolytic and antidepressant properties. Phenelzine sulfate irreversibly binds to MAO, thereby blocking the oxidative deamination of monoamines resulting in an increased concentration of biogenic amines and a concurrent decrease in catabolism of monoamine neurotransmitters, norepinephrine and serotonin, in the brain. In addition, through its primary metabolite phenylethylidenehyrazine (PEH), phenelzine causes elevated GABA levels in the caudate-putamen and nucleus accumbens thereby exerting its anxiolytic effects.