Monoamine Oxidase Inhibitor

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The first antidepressants were discovered inadvertently in the 1950s when a tuberculosis medication, iproniazid, was found to improve patients’ moods (Preston, O’Neal, & Talaga, 2008). Iproniazid (Marsilid, Iprozid, Rivivol) and other monoamine oxidase inhibitors (MAOIs) block MAO, a substance that breaks down the norepinephrine, serotonin, and dopamine stored at the ends of neurons. This makes more of these neurotransmitters (chemical messengers) available for neurotransmission (communication between neurons; Preston et al., 2008).

This discovery led to the development of the fist classs of antidepressant medication, the MAOIs. MAOIs include iproniazid, isocarboxazid (Marplan), pargyline (Eutonyl), phenelzine (Nardil), selegiline (Deprenyl, Emsam), and tranylcypromine (Parnate).

In addition to the MAOIs, other types of antidepressants include tricyclics, selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), norepinephrine reuptake inhibitors, and atyptical antidepressants.

One type of atypical antidepressant is the reversible inhibitor of monoamine oxidase A (RIMA), which is a variant of the MAOI.

MAOI antidepressants are used to treat clinical depression and anxiety (e.g., social anxiety, generalized anxiety, panic disorder, posttraumatic stress disorder, and bulimia). Some MAOIs (e.g., Selegiline, an MAO-B inhibitor) are used in the treatment of Parkinson’s disease. MAOIs are particularly useful to treat refractory (treatment-resistenat) depression.

Owing to potentially fatal severe hypertensive (high blood pressure) reactions, MAOIs are generally used only after other antidepressants have failed.

Severe hypertensive reactions can be caused by taking MAOIs with decongestants or other antidepressants or by eating foods high in tyramine (e.g., salami, chicken liver, some sausages, some types of fish, bologna, beef bouillon, sauerkraut, some types of beer or wine). Other side effects of MAOIs may include sedation, agitation, confusion, insomnia, sudden drop in blood pressure, and edema (Preston et al., 2008).

Combining MAOIs with other antidepressants or drugs, such as opioids, stimulants (e.g., amphetamines, cocaine), psychedelics (e.g., MDMA of Ecstasy), or herbs (e.g., St. John’s wort), can cause serotonin syndrome—a potentially lethal condition resulting from toxic levels of serotonin in the central nervours system. Symptoms of serotonin syndrome may include rapid heart rate, sweating, shivering, dilated pupils, tremor or twitching, muscular rigidity, elevated temperature, confusion, agitation, delirium, hallucinations, coma, or death.

Sudden discontinuation of MAOIs can result in withdrawal symptoms, which may include dizziness, nausea, sweating, insomnia, tremor, or confusion. A schedule for tapering off antidepressants should be discussed with a doctor. Risk of taking MAOIs while pregnant (including harm to the mother to the fetus) cannot be ruled out (Preston et al., 2008).

To avoid potentially harmful side effects and drug interactions, health care consumers should be sure that their doctors and pharmacist are aware of all medications they are taking, including over-the-counter medications, herbs and natural remedies, and dietary supplements.

See also:
  1. American Psychiatric Association—Healthy Minds Web site:
  2. Depression and Bipolar Support Alliance Web site:
  3. National Alliance on Mental Illness Web site:
  4. Preston, J.D., O’Neal, J.H., & Talaga, M.C. (2008). Handbook of clinical psychopharmacology for therapists (5th ed.). Oakland, CA: New Harbinger.