Monoamine oxidase (MAO) is an enzyme widely distributed in animals; other names are adrenaline oxidase and tryaminase. Its function in the body is the breakdown of certain biologically active amines, three of the most important of which are the tryptamine derivatives, the catechol amines (such as adrenaline and dopamine), and histamine. Monoamine oxidase inhibitors are used as antidepressants.