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Side Effects of


Description: MAOIs (monoamine oxidase inhibitors) are an older class of antidepressant that carry the risk of considerable side effects and drug interactions. Modern MAOIs used to treat depression (mostly atypical depression), include phenelzine, selegiline, or tranylcypromine. Selective MAOI inhibitors (selegiline, rasagiline) may be prescribed to people with Parkinson’s disease.
(Australasian Psychiatry “MAOIs – does the evidence warrant their resurrection,” Aug 2016).

Mechanism of Action

As the name implies, an MAOI blocks the action of a chemical called the “monoamine oxidase” enzyme. Inhibiting the monoamine oxidase enzyme makes several chemical levels rise. These include the common neurotransmitters (brain chemicals) dopamine, serotonin, and norepinephrine. (Journal of Clinical Psychiatry “Mechanism of action of antidepressant medications,” Apr 1990).

Serious Side Effects of MAOIs: Hypertensive Crisis and Serotonin Syndrome

People who eat substantial amounts of tyramine in conjunction with MAOIs may experience an unsafe increase in norepinephrine levels. Too much norepinephrine may lead to a state called “hypertensive crisis,” which is a dangerously high blood pressure level. Another potentially severe side effect of MAOIs is serotonin syndrome, which causes elevated blood pressure, agitation, tremor, sweating, and other symptoms. In severe cases, serotonin syndrome may lead to seizures, muscle destruction, coma and death. (CNS Drugs “Current place of monoamine oxidase inhibitors in the treatment of depression,” Oct 2013).

Common Side Effects of MAOIs

Nausea occurs in more than 10% of people who take an MAOI, according to Journal of Clinical Psychiatry “Mechanism of action of antidepressant medications” (Apr 1990).

Other relatively common side MAOI effects, according to CNS Drugs “Current place of monoamine oxidase inhibitors in the treatment of depression” (Oct 2013) include:

  • Headaches
  • Sleeplessness
  • Dizziness
  • Dry mouth
  • Drowsiness
  • Low blood pressure
  • Abdominal pain
  • Urinary problems
  • Understand Your Risks with the Rxight® Genetic Test

    The Rxight® pharmacogenetic testing program is designed to provide patients who are considering an MAOI or who are currently on an MAOI with a profile of their own gene variants and the corresponding chemicals in the liver responsible for breaking down and processing MAOIs. Additionally, an entire suite of over 200 prescription and over-the-counter medications across 50 clinically relevant drug classes are analyzed based on a simple DNA cheek swab.

    How Does Pharmacogenetic Testing Work?

    PGx testing with Rxight® specifically tells you if your genetic makeup makes the activity of these enzymes higher or lower than normal, thus making some medications ineffective or, worse, potentially dangerous or fatal. This could have important ramifications for side effects and drug effectiveness, and guide your prescriber in finding the safest dose or if necessary an alternative medication.
    (Read more about psychiatric medication side effects and genetic testing for antidepressant response.)


    Contributors to this Article:
    Michael Sapko, MD, PhD; Deborah Kallick, PhD, Medicinal Chemistry

    Read more about Rxight® Genetic Testing For Depression Medication