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What Are MAO Inhibitors?

Just your average apothecary (pharmacist), feet firmly planted behind the pharmacy counter, whose mortar and pestle are hitched to a star.


MAO Inhibitors for Depression

If you have ever looked at the warnings on the back of a cough/cold product you may have run across something like this: "Do not take if you are currently using an MAO inhibitor." An MAO what? This article briefly describes the MAO inhibitor family of prescription medications and explains some of the serious and potentially life-threatening drug interactions that can occur when taking one of these drugs.

MAO stands for Monoamine Oxidase, which is an enzyme responsible for metabolizing neurotransmitors such as seratonin and norepinephrine. This family of prescription medications are used primarily for treating depression, although one MAO Inhibitor, selegeline, is used to treat Parkinson's Disease.

The 4 MAO Inhibitors currently available and used to treat depression are:

  • Isocarboxazid (Brand name Marplan)
  • Phenelzine (Brand name Nardil)
  • Tranylcypromine (Brand name Parnate)
  • Selegeline (Brand name Emsam, a transdermal patch)

MAO inhibitors are only available by prescription.


How Do MAO Inhibitors Work?

MAO Inhibitors (also called MAOI's) work by interfering with the enzyme responsible for metabolizing seratonin, epinephrine, dopamine and norepinephrine. By binding to this enzyme they effectively increase the concentration of these neurotransmitters which in turn causes changes within specific areas of the CNS (central nervous system). These changes have been shown to result in a decrease in symptoms associated with depression.

I like to illustrate it this way: Neurotransmiters are like mental mail carriers. Monoamine oxidase is like a big scary watch-dog that keeps eating the mail carriers and thus keeping him from delivering your mail! MAOI's are like a nice big juicy bone that we give to the dog to keep him busy and distracted so that the mail carrier can do his work. Did that make sense? It is a bit over-simplified for sure, but it gives you a rough (or should I say "ruff ruff"?) idea of how MAO inhibitors work.

MAO Inhibitor Warning


What Risks are Associated with MAO Inhibitors?

MAO Inhibitors do a good job preventing MAO from metabolizing these important neurotransmiters. However, they are so effective, that they can also create problems, particularly with certain over-the-counter cold remedies and specific food items.

Medications to Avoid:

Because MAO Inhibitors increase norepinephrine (a powerful blood vessel constrictor) it is important that patients taking one of these products do NOT ingest any other medication which could potentially increase norepinephrine levels even further. The consequences of such a combination could be, in some cases, fatal. Such medications include:

  • Pseudoephedrine (A nasal decongestant, now only available "behind the counter" in a pharmacy, but very commonly included in cold remedies)
  • Phenylephrine (A decongestant used in place of pseudoephedrine in many cough/cold products)
  • Amphetamine or Dextroamphetamine (Often used, by prescription, to treat ADHD)
  • Naphazoline and Oxymetazoline (In nasal sprays)
  • Isometheptene (ingredient in the prescription drug Migranal)
  • Methylphenidate (also known as Ritalin)
  • Meperidine (the ingredient in prescription Demerol, for pain)
  • Eye drops with decongestants should also be avoided.

This list is not comprehensive, but covers some of the most significant culprits. Be sure to read labels carefully if you are currently taking an MAOI. Be especially careful about taking herbal products that may have stimulants in them. Because of these risks, MAO inhibitors are not used as frequently today as they had been in the past.

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Foods to Avoid

Monoamine oxidase also exists in our intestinal tract and aids in the break down of a substance known as Tyramine. MAO inhibitors interfere with this process, and will allow large amounts of Tyramine (from foods or beverages containing tyramine) to enter the the blood stream and contribute to a sequence of events that could lead to a hypertensive crisis (ie a very dramatic, potentially fatal, elevation of the blood pressure).

Therefore, patients on MAO inhibitors must completely avoid foods and beverages which contain significant amounts of tyramine. These include, but are not limited to:

  • Aged cheese and meats
  • Smoked meats or pickled meats
  • Liver
  • Anchovies
  • Sauerkraut
  • Avacado
  • Bananas
  • Pepperoni
  • Salami
  • Raisons
  • Caffeine should be used sparingly
  • Avoid wine, sherry, beer, and hard liquor.

Note, patients must wait for 14 days following discontinuation of an MAO inhibitor before they can safely consume any of these foods.

More Information

For more information on MAO Inhibitors, side-effects, or manufacturer's guidelines, see the following links:

EMSAM (patch) Manufacturer's Website

Nardil by Pfizer

Marplan by Validus Pharmaceuticals

Parnate Prescribing Information

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.


Jason Poquette (author) from Whitinsville, MA on December 17, 2012:

Hi Syl,

Yes, Yohimbine should not be combined with an MAO inhibitor like Marplan, Nardil or Parnate. Glyfomin is the brand name for metformin, though not available in the U.S. by that name. There does not appear to be any known interactions between the 3 products you mention. Always talk to you doctor when considering a change in your medication. Also, keep an eye on your blood sugars just to be safe. Best wishes.