Publisher Summary This chapter provides an overview of antidepressant drugs. Monoamine oxidase exists in at least two substrate forms; type A oxidatively deaminates 5-hydroxytryptamine and noradrenaline and is selectively inhibited by clorgyline. Type B deaminates phenylethylamine and is selectively inhibited by (-) deprenyl. Dopamine is a B substrate in human brain that led to trials of deprenyl as an adjunct in the management of Parkinson's disease to potentiate the effects of levodopa. Chloripramine (clomipramine) compound has attracted particular interest because of an action on pituitary hormone release which occurs with major tranquillizing drugs but not with other antidepressants. Mianserin drug appears to have fewer anticholinergic side effects than tricyclic antidepressants. A 66-year-old man treated with tranylcypromine 10 mg three times a day has been reported to have developed inappropriate secretion of antidiuretic hormone. A water load test revealed marked differences before and during therapy.