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Monoamine Oxidase Inhibitor Medications
Monoamine oxidase inhibitors (MAOIs) were the first medications approved for the treatment of depression. Monoamine oxidase is an enzyme responsible for clearing certain neurotransmitter chemicals from the brain, among other tasks. When the activity of this enzyme is restricted, the brain has more norepinephrine, serotonin, and dopamine available to send important messages and regulate mood states. Most new antidepressants do not have such a broad mechanism of action. This monoamine oxidase enzyme is also important in the digestive process, which explains some of the possibly severe interactions and side effects resulting from taking MAOIs.
The most commonly prescribed MAOIs are Marplan (isocarboxazid), Nardil (phenelzine), Emsam (selegiline), and Parnate (tranylcypromine). Typical side effects of these medications include drowsiness, dizziness, low blood pressure, sexual dysfunction, and nervousness. Side effects are not usually severe enough to cause someone to stop taking their medication. Most MAOIs come in the form of a pill, but recently manufacturers have also developed an Emsam skin patch. The skin patch is thought to be more easily tolerated and cause fewer side effects, especially at lower doses.
People taking MAOIs must follow strict dietary and medication guidelines to avoid serious adverse reactions. Certain substances in aged and fermented foods are toxic when the body is unable to remove them. MAOIs can also have dangerous drug interactions with other antidepressants, antihistamines, pain medications, and certain herbal supplements, such as St. John's wort. It's also important to taper off one's dosage of MAOIs rather than stopping them suddenly. Severe withdrawal symptoms are possible, including psychosis and convulsions.
Today, monoamine oxidase inhibitors are often seen as a "last resort" treatment when other antidepressants have failed. For whatever reason, some individuals do not respond well to newer classes of antidepressants. In these cases, doctors often fall back upon older formulations, such as MAOIs or tricyclics. Researchers believe that genetic profiling may someday offer guidance to doctors in selecting an antidepressant, but such innovations are not available at this time.
MayoClinic.com. (n.d.). Monoamine oxidase inhibitors (MAOIs). Retrieved April 23, 2012, from
National Institute of Mental Health. (n.d.). Mental health medications . Retrieved April 23, 2012, from
Last Update: 06-28-2012
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