Monoamine Oxidase Inhibitors: Uses & Side Effects

Monoamine oxidase inhibitors (also called MAO inhibitors or MAOIs) block the actions of monoamine oxidase enzymes.

Monoamine oxidase enzymes are responsible for breaking down neurotransmitters such as dopamine, norepinephrine, and serotonin in the brain. Low levels of these three neurotransmitters have been linked with depression and anxiety. By blocking the effects of monoamine oxidase enzymes, MAOIs increase the concentration of these three neurotransmitters and are useful at relieving symptoms associated with depression, such as sadness or anxiety.

MAOIs are typically only used when other antidepressants have proven ineffective, because they have a higher risk of drug interactions than standard antidepressants and can also interact with certain types of food such as aged cheeses and cured meats. They also tend to have more side effects than standard antidepressants and may cause a withdrawal syndrome on discontinuation.


MAOIs may be used to treat the symptoms of depression, such as sadness, anxiety, or worry, that have not responded to other antidepressants. They should not be used to treat severe depression or bipolar disorder.

There are some other drugs that also inhibit monoamine oxidase enzymes (in addition to having other properties), but are not used for the treatment of depression. These drugs should not be taken within 14 days of another MAOI nor with food or beverages that have a high tyramine content. Some resources may not list these drugs as MAOIs even though they inhibit monoamine oxidase enzymes.

Side effects

One of the more common side effects associated with MAOIs on drug initiation is low blood pressure when going from a standing to a sitting position (called orthostatic hypotension). In most people this can be managed by slowly increasing the dosage of the medication, giving split doses, and increasing fluid intake.

Other common side effects when starting therapy include:

  • Dizziness
  • Drowsiness
  • Insomnia
  • Nausea.

Insomnia may be helped by not giving doses too late in the evening.

Side effects that tend to occur with regular, long-term therapy include:

  • Edema (fluid retention)
  • Muscle pains
  • Myoclonus (spasmodic, jerky, muscle contractions)
  • Paraesthesias (abnormal sensations or prickling in the nerves)
  • Sexual dysfunction
  • Weight gain.

Paraesthesias may be helped by pyridoxine supplementation.

Keywords: Monoamine Oxidase Inhibitors.

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.