monoamine oxidase (MAO) (mon-oh-ay-meen) n. an enzyme that catalyses the oxidation of a large variety of monoamines, including adrenaline, noradrenaline, and serotonin. Monoamine oxidase is found in most tissues, particularly the liver and nervous system. See also MAO inhibitor.

monoamine oxidase (MAO) An enzyme that breaks down monoamines (e.g. adrenaline and noradrenaline) in the body by oxidation. Drugs that inhibit this enzyme are used to treat forms of depression.

monoamine oxidase Enzyme that oxidises amines; inhibitors have been used clinically as antidepressant drugs, and consumption of amine‐rich foods such as cheese may cause a hypertensive crisis in people taking the inhibitors.