Some examples of monoamine oxidase inhibitors are Marplan, Nardil, Emsam and Parnate, according to Mayo Clinic. Patients typically take these drugs, though Selegiline is available as a transdermal patch.
MAOIs prevent an enzyme called monoamine oxidase from taking dopamine, serotonin and norepinephrine from the brain, says Mayo Clinic. This action is thought to improve the patient's mood.
The side effects of MAOIs include dry mouth, nausea, headache, diarrhea and constipation. MAOIs have largely been replaced by antidepressants that do not have their side effects, says Mayo Clinic. As of 2015, they are prescribed when newer forms of antidepressants have proven ineffective.