Marplan, Nardil, Emsam and Parnate are some monoamine oxidase inhibitors the Food and Drug Administration has approved to treat depression, according to Mayo Clinic. MAOIs are effective for the treatment of depression but have largely been replaced by safer antidepressants that result in fewer side effects.
MAOIs help in the treatment of depression by affecting the levels of neurotransmitters in the brain, states Mayo Clinic. Specifically they prevent the monoamine oxidase enzyme from removing serotonin, dopamine and norepinephrine from the brain, resulting in better communication between brain cells and a corresponding improvement in mood. Because they also have an affect on other neurotransmitters, MAOIs can cause side effects, including headache, nausea and insomnia.