Monoamine Oxidase Inhibitor Antidepressants (MOAIs)


There are a number of different MAOI antidepressants.

Brand name Chemical name
Parnate Tranylcypromine
Nardil Phenelzine

How MAOIs work

Monoamine Oxidase Inhibitor Antidepressants (MAOIs) work by binding with and stopping the activity of monoamine oxidase, an enzyme found throughout the body. Monoamine oxidase breaks down a number of chemicals made and used by the body and brain. These chemicals include noradrenaline (also called norepinephrine) and serotonin as well as other chemicals made by the cells in the brain. Noradrenaline and serotonin are neurotransmitters by which the brain cells connect and communicate with each other. Monoamine oxidase inhibitor antidepressants increase the amount of these chemicals in the brain.

MAOIs also increase the amounts of other chemicals in the body and especially some chemicals which are found in food and other medications. Because they increase chemicals other than noradrenaline and serotonin MAOIs can have serious and dangerous side effects if you are not careful about certain foods and other drugs. Read very carefully the sections below on drug and food interactions.

Over many years of study and use MAOIs have been shown to improve symptoms of depression and anxiety.

Side effects

Common side effects include:

  • Dizziness on standing
  • Sleep disturbance at night
  • Sleepiness during the day (care needed with driving)
  • Dry mouth
  • Tremor (slight shake of muscles of arms and hands)
  • Difficulty passing urine (especially in men)

Effect on weight and sleep

  • Weight loss is more common than weight gain
  • Difficulty getting to sleep and broken sleep
  • Intense daytime sleepiness


MAOIs can cause:

  • lowered blood pressure especially on standing. This may cause fainting.
  • Dangerously high blood pressure in combination with certain foods and medications
  • irregular heart beat


An overdose of an MAOI is dangerous. Deaths have occurred with large overdoses. An overdose causes confusion and coma. It can also cause high blood pressure and stop the heart. Go to hospital immediately.

Effect with alcohol

MAOIs may increase the effect of alcohol and alcohol increases the drowsiness effect of MAOIs.

Interactions with other drugs

A number of medications and drugs can cause a dangerous increase in blood pressure when taken with an MAOI. These include:

  • Other antidepressants
  • Stimulant drugs such as Ritalin and Dexamphetamine (used to treat Attention Deficit Hyperactivity Disorder (ADHD))
  • Cold cures bought over the counter can be dangerous as they contain pseudo-ephedrine. (Plain Paracetamol (eg Panadol, Panamax) are safe.)
  • Nasal decongestants (tablets, drops or spray)
  • Hay-fever and sinus medications
  • Asthma inhalant medications
  • Anti-appetite medicines
  • Some local anaesthetics (including dental anaesthetics).
  • Pethidine and codeine
  • Illicit drugs such as speed or ecstasy
  • 'Pep' pills
You should tell anyone prescribing you medicines that you are taking MAOIs

If you experience severe headache, chest pain or palpitations, have your blood pressure checked immediately.

MAOI effects may last longer than one week after stopping the medication. This means that interactions between medications can occur up to two weeks after stopping.

MAOIs increase the effect of any drug that causes drowsiness or lowered blood pressure. (However, they can reduce the effect of some antihypertensive (blood pressure controlling) medications).

These interactions between MAOIs and other medications may mean that the dose of the other medications you are taking will need to be adjusted.

Interactions with foods

Some foods contain tyramine which can raise blood pressure with MOAIs. You should check with your doctor what these are, but examples of some foods you should avoid while taking MAOIs (because they can cause serious problems) are:

  • Tasty cheese (eg, cheddar. NB: Cottage and ricotta cheeses are all right)
  • Chianti wine, sherry, some beer (including non-alcoholic beer)
  • Caviar, pickled herring, anchovies, liver
  • Dry sausage (including Genoa salami, hard salami, pepperoni)
  • Broad bean pods (fava bean pods), sauerkraut
  • Soy sauce, yeast extract, miso

When they must not be taken

MAOIs must not be taken at the same time, or soon after, using any of the drugs or medicines listed above.

MAOI effects may last longer than one week after stopping the medication, so interactions between medications and food can occur up to two weeks after stopping.

Use in Pregnancy and Breast Feeding

MAOIs have not been shown to be harmful to the foetus in pregnancy although there have been few studies in humans. MAOIs appear in breast milk. There have been no studies of the safety of this for babies. If the mother's treatment needs to continue the manufacturers recommends that the baby be weaned. Otherwise, the manufacturers recommend that the antidepressant be stopped if a mother is breast feeding.

Use in children

MAOIs are not recommended for children.

Withdrawal effects

Antidepressants are not addictive. However, some people experience withdrawal effects on stopping their antidepressant. Reactions vary between medications and between people. The effect of both Parnate and Nardil stop slowly. As a result, although withdrawal effects have been reported, they are uncommon with MAOIs.

Dosage and time of dose

The starting dose is usually very small and is gradually increased. This allows the dose to be increased to levels that work against depression. Some people will need higher doses.

Morning dosage is most common as most people find that MAOIs disturb sleep. The time of day the dose is taken does not change its effectiveness against depression.

If a dose is missed take it as soon as possible. If a morning dose is missed it can be taken later in the morning. Do not take it later than that but take only the ordinary morning dose next morning.

Name Chemical name Common dose* Most common time of dose
Parnate Tranylcypromine 20mgm - 60mgm Morning
Nardil Phenelzine 30mgm - 90mgm Morning
* with careful observation these doses may be considerably increased by your doctor

How long do you need to be on a medication?

You will need to take the antidepressant for at least 6 to 9 months after your symptoms disappear. Stopping your antidepressant too early increases your chances of suffering a recurrence of depression.

Are there problems with very long term use?

MAOIs have been in use for more than 40 years. Some people have taken them for that length of time. No extra problems have emerged beyond the common side effects mentioned above.

Last reviewed and updated: 15 January 2007