Monoamine oxidase inhibitors (MAOIs) are a class of antidepressant drugs prescribed for the treatment of depression. Due to potentially serious dietary and drug interactions they are used less frequently than other classes of antidepressant drugs ( for example tricyclic antidepressants and selective serotonin reuptake inhibitors). However in some cases unresponsive to other treatments they are tried, sometimes with a marked improvement.

In the past they were prescribed for those resistant to tricyclic antidepressant therapy, but newer MAOIs are now used as an alternative to tricyclics. They are also used for treating agoraphobia. MAOIs, in their original form presented an unusual problem for the prescribing physician. If a physician was prescribing MAOIs for depression, he/she had to take into consideration the fact that he/she was offering the patient a ready, though unpleasant, route to suicide.

MAOIs act by inhibiting the activity of monoamine oxidase preventing the breakdown of monoamine neurotransmitters and so prolonging their effect. Some MAOIs can potentiate the action of a number of other drugs; they also inhibit the metabolism of the amino acid tyramine, so that tyramine-containing foods can trigger hypertensive attacks, occasionally with fatal results. Examples of tyramine-containing foods include such common foods as liver, fava beans, Chianti and other aged wines, aged cheeses, meat extracts (e.g. Bovril) and yeast extracts (e.g. Marmite, Vegemite). However, newer types of MAOIs (reversible MAOIs such as monclobemide) do not have these effects.

Combined use of MAOIs and other serotonergenic drugs can lead to serotonin syndrome.

MAOIs are also used to enhance the effect and duration of N,N-dimethyltryptamine based hallucinogens, commonly used by shamans in South American indiginous tribes to extend the duration of DMT based rituals.

Monoamine oxidase inhibitors include:

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