Monoamine Oxidase Inhibitors (MAOIs) are a class of Antidepressants which can be used to treat various mental health conditions, including Depression.

MAOIs were the first class of antidepressants to be developed. However, MAOIs are rarely used in modern times, due to the demands on diet that they cause, interactions with other medicines, and severity of danger in overdose.

MAOIs have largely been replaced by Selective Serotonin Reuptake Inhibitors (SSRIs) and Serotonin and Norepinephrine Reuptake Inhibitors (SNRIs).

MAOIs are still sometimes used, especially in cases of Treatment-Resistant Depression. MAOIs, like other antidepressants, are most effective when used in conjunction with a form of talking therapy.

MAOIs are some of the oldest antidepressants

Information on MAOI Antidepressants

It normally takes between four and six weeks for any antidepressant’s full effectiveness to be felt. However, some people will see improvements within a few weeks.

It is important to take an antidepressant how and when a Doctor has advised. This is even more important when taking an MAOI.

This involves taking the correct dose at the right time, and taking the medication on a consistent basis. It is also important to not take more than one dose at a time to make up for a forgotten dose.

A low dose will initially be prescribed. Once the patient has seen a decrease in their symptoms, it is important to continue to take the medicine for a while, as this will improve the chances of symptoms not coming back.

What conditions are MAOI Antidepressants used for?

MAOI antidepressants can be used in the treatment of a few different mental health conditions. They are normally only ever prescribed in cases of treatment-resistant conditions. For example, this might be when a person has tried multiple antidepressants without success.

  • Depression
  • Anxiety
  • Eating Disorders
  • Personality Disorders
  • Obsessive-Compulsive Spectrum Disorders

What are the different types of MAOI Antidepressants?

There are just a few diffetrent MAOIs that are licensed for use in the United Kingdom for mental health conditions.

  • Isocarboxazid (Marplan)
  • Moclobemide (Manerix)
  • Tranylcypromine (Parnate)
  • Phenelzine (Nardelzine)

How do MAOI Antidepressants work?

It isn’t entirely known how MAOIs work. Like other antidepressants, they target a group of chemicals in the brain called neurotransmitters.

MAOIs prevent an enzyme called monoamine oxidase from removing certain neurotransmitters. MAOIs work on many different neurotransmitters – namely serotonin, dopamine and norepinephrine. These chemicals appear to be linked to mood.

Side Effects of MAOI Antidepressants

Side effects are common with MAOIs. The main reason why MAOIs have largely been replaced is due to their effect on diet, as well as their interactions with other medicines.

It is important to note that the side effects for each medicine within this class differs slightly. With any antidepressant, a Patient Information Leaflet will be included in the box. This leaflet provides an exhaustive list of side effects.

Side effects from MAOIs can be difficult to live with. Sometimes, side effects will last just a few days as the body adjusts to the medication. However, some side effects may be persistent.  

Common side effects of MAOIs include dry mouth, dizziness, headaches, sedation, weight gain/loss, sexual dysfunction.

When taking MAOIs, special precautions are needed. Foods or beverages including tyramine should be avoided. A high level of tyramine consumption can cause hypertensive crisis – which is often fatal. Foods and drink that include tyramine include meat, fish, aged cheeses, avocados, alcohol and more.

Serious side effects include suicidal thoughts, seizures, chest pain, psychosis or any abnormal behaviour. An overdose should be avoided, as it can cause the potentially fatal Serotonin Syndrome.

MAOIs also have serious interactions with a range of other medicines – including other antidepressants, painkillers, stimulants, antipsychotics and many others. In the event of any serious side effect, it is important to contact the emergency services.

If side effects from antidepressants persist for a few weeks, or provide discomfort, it may be worth switching medication to an alternative antidepressant – although this should be done in conjunction with a Doctor.

Cautions of MAOI Antidepressants

It is important to thoroughly read the Patient Information Leaflet that comes with your medication. The leaflet will include specific cautions that should be taken into consideration when taking the medicine.

General considerations when taking antidepressants include:

  • Tell a Doctor about any medicine or substance that is currently being used – such as Herbal Remedies like St. John’s Wort
  • Avoiding alcohol in the first few days of treatment, to allow the body to get used to the medication.
  • Any antidepressant can react unpredictably with illegal drugs; therefore it is advisable to not use recreational drugs when undergoing antidepressant therapy.
  • Studies show that people under the age of 25 taking antidepressants are at heightened risk of suicidal ideation [1]. Therefore, it is important to exert caution during treatment.
  • Antidepressants shouldn’t routinely be taken during pregnancy or breastfeeding. It is important to discuss this with a Doctor.


It is important to state that MAOIs are effective antidepressants. Over the years, they have helped many people. For those that are prescribed them, they will have a good chance of seeing an improvement in their symptoms.

However, given how newer and safer antidepressants are now available, it has made MAOIs less desirable. But the option is always there if needed.

See Also



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[1] Leslie, L. K., Newman, T. B., Chesney, P. J., & Perrin, J. M. (2006). The Food and Drug Administration’s Deliberations on Antidepressant Use in Pediatric Patients. Pediatrics. 116 (1): p195-204. DOI: