Monoamine oxidase inhibitors (MAOIs) are antidepressant medications that are also sometimes used in patients suffering from Parkinson's disease, according to Mayo Clinic. MAOIs are the oldest type of antidepressant and have been replaced over time by safer, modern types of antidepressants, though they are sometimes still used, as of 2014.
MAOIs treat depression by increasing the levels of the neurotransmitters serotonin, dopamine and norepinephrine within the brain, explaisn Mayo Clinic. MAOIs are also known to affect neurotransmitters within the brain other than those related to depression. Despite being more rarely used than other antidepressants, they are shown to be more effective in some treatment-resistant cases. Isocarboxazid, phenelzine, selegiline and tranylcypromine are the four MAOIs that have been approved by the United States Food and Drug Administration.
A subtype of depression known as atypical depression is effectively treated using MAOIs, according to Wikipedia. MAOIs are generally considered to be a last-resort treatment option for depression due to potentially lethal complications related to their use.
MAOIs are used less often than other types of antidepressants because they often have dangerous interactions with other medications or chemicals that may be found within common foods. Eating certain foods while taking MAOIs may increase blood pressure to dangerous levels, according to Mayo Clinic
MAOIs are not commonly used due to their many side effects. They are typically used when other antidepressants are ineffective. Dry mouth, insomnia, headache, and diarrhea are common side effects of MAOs. Severe side effects requiring medical symptoms include low blood pressure and difficulty urinating, according to Mayo Clinic.
Marplan, Nardil, Ensam and Parnate are MAO inhibitors, according to Mayo Clinic. They are consumed orally. Selegiline is another MAOI. It is taken externally as a patch placed on the skin.