What Drugs Are Considered Mao Inhibitors?

Monoamine oxidase inhibitors--also known as MAO inhibitors or MAOIs--are a group of drugs first developed in the late 1950s for the treatment of major depression. These drugs inhibit the enzyme monoamine oxidase, which is present in high concentrations in the brain and liver. Blocking this enzyme causes increased levels of neurotransmitters, including dopamine, melatonin, norepinephrine, epinephrine and serotonin. Newer antidepressants have limited the use of MAOIs. However, MAOIs continue to have a role for a select group of people with depression. Additionally, selective MAOIs can alleviate the symptoms of Parkinson's disease.

Isocarboxazid

The U.S. Food and Drug Administration (FDA) first approved isocarboxazid for the treatment of major depression in 1959. This drug inhibits both forms of the monoamine oxidase enzyme, which causes increased neurotransmitter levels in the brain and in nerves elsewhere in the body. Isocarboxazid and other MAOIs interact with many other medications and foods. If you are on an MAOI, check with your doctor before beginning any other medicine to be sure it is safe for you.

Tranylcypromine

Tranylcypromine was first approved by the FDA for use in the treatment of major depression in 1961. It causes irreversible blockade of both forms of the monoamine oxidase enzyme. Levels of the neurotransmitters epinephrine, norepinephrine and serotonin are effectively increased by tranylcypromine. Because it has many side effects and drug interactions, doctors typically prescribe this medication only if other antidepressants fail to provide symptom relief.

Phenelzine

Phenelzine has been in use in the U.S. since 1961 for the treatment of depression. The National Institute of Mental Health reports 14.8 million adults in the U.S. have major depression. Of this group, a subset have a clustering of symptoms known as atypical depression. Eating and sleeping excessively, early age of depression onset, and variability in mood despite underlying sadness are the hallmark features of atypical depression. In a 2007 review article on the treatment of atypical depression published in the "Journal of Clinical Psychiatry," Dr. J. Stewart noted that phenelzine remains the most effective antidepressant for this variant of depression, with improvement seen in roughly two-thirds of people treated with the drug.

Rasagiline and Selegiline

Rasagiline and selegiline are selective MAOIs, reacting with only one of the two forms of the monoamine oxidase enzyme--the form that predominates in the brain. By blocking this enzyme, rasagiline and selegiline effectively increase the concentration of the neurotransmitter dopamine in the brain. Dopamine levels are abnormally low in people with Parkinson's disease. Rasagiline and selegiline are prescribed to alleviate the symptoms of Parkinson's disease by raising brain dopamine concentration. According to the National Institute of Neurological Disorders and Stroke, more than 500,000 Americans have Parkinson's disease.