How MAOIs work

Antidepressants such as MAOIs ease depression by controlling chemical messengers called neurotransmitters that carry messages between brain cells and affect mood. MAOI antidepressants block an enzyme called monoamine oxidase from doing its work. This enzyme breaks down neurotransmitters known as norepinephrine, serotonin and dopamine, sometimes lowering their levels too much. By blocking this process, MAOIs can raise the levels of these neurotransmitters in the brain and ease depression.

MAOIs also affect other neurotransmitters in the brain and digestive system, which can cause side effects. MAOIs sometimes are used to treat conditions other than depression, such as Parkinson's disease.