What they are

Monoamine oxidase inhibitors (MAOIs) are a group of medicines that are used in the treatment of depression and anxiety. Since other antidepressants, such as the tricyclics (TCAs) and selective serotonin reuptake inhibitors (SSRIs), have become available, MAOIs have been prescribed much less.

Three MAOIs have been available for many years: isocarboxazid (Marplan), phenelzine (Nardil), and tranylcypromine (Parnate, Parstelin).

One MAOI, moclobemide (Manerix), is much newer. It has a similar action but different side-effects, and is a "reversible inhibitor of monoamine oxidase-A" or a RIMA. It does not usually interact with food in the same way as traditional MAOIs.

Their effects

How they work

Our brains contain chemicals called neurotransmitters, which help the brain to function. In depression, the levels of some of these neurotransmitters can be disturbed. MAOIs help to return the levels of these chemicals towards normal, by reducing their breakdown. They work by preventing an enzyme, called monoamine oxidase, from working.

How well they work

MAOIs do not work as well as TCAs or SSRIs in people with moderate or severe depression.

MAOIs appear to work well in people with atypical depression (depression with features which are opposite to the usual symptoms of depression, such as increased sleep, increased appetite, and increased weight).

There is some evidence that MAOIs can lift mood in depressed people whose mood has not responded to antidepressants such as TCAs or SSRIs.

People starting MAOIs should notice improved sleep within a few days, but may not notice improved mood for a fortnight or more.

Who should take them

MAOIs are not widely used, as they do not work as well as SSRIs or TCAs in most types of depression, and most of them need strict dietary restrictions.

However, they are a possible alternative to SSRIs or TCAs if:

• the depression is atypical
• SSRIs or TCAs produce troublesome side-effects, or
• the depression is resistant to treatment

What should I do if I miss a dose?

If you miss a dose of an MAOI, check how long it is since you should have taken it. If it is a few hours or less, take the missed dose. Otherwise, miss that dose, and just take your next scheduled dose. Do not double your next dose to compensate for the missed dose.

Their side-effects

Side-effects

Common side-effects include: dry mouth, insomnia, increased heart rate, and drowsiness. Others include: dizziness, difficulty sleeping, headache, weakness, and constipation.

If stopped suddenly, MAOIs may cause symptoms including restlessness, anxiety, difficulty sleeping, headache and sickness. Therefore, MAOIs should be stopped gradually, over a period of about 4 weeks. Before stopping MAOIs, ask your doctor for advice.

If taken with certain foods or drinks, MAOIs may cause a dramatic reaction, which can be dangerous. This is because some foods naturally contain a chemical called tyramine which affects blood pressure. MAOIs interact with this chemical. As this can be dangerous, food and drinks containing tyramine should be avoided. It is important to only eat fresh foods and avoid any food that is suspected to be stale or going "off". Click here for further information on dietary restrictions and a printable dietary reference card.

Who should avoid taking them

MAOIs should not be used:

• in people with liver disease or abnormal liver blood tests, history of stroke or transient ischaemic attacks ('mini strokes' or TIAs), phaeochromocytoma, or mania;
• in people taking medicines for cough, cold, flu, or hayfever, including those available over the counter;
• in people taking other MAOIs, SSRIs, reboxetine, venlafaxine, carbamazepine, strong (opioid) pain killers, such as pethidine, and some other medicines (for a full list of possible drug interactions, please see the British National Formulary);
• in people who drink excessive alcohol.

MAOIs should be used carefully:

• in the elderly;
• in people with blood disorders, sugar diabetes (diabetes mellitus), epilepsy, heart disease, over active thyroid (hyperthyroidism), liver disease, phaeochromocytoma, and porphyria;
• during pregnancy or breast feeding (note, there is no evidence that MAOIs harm the foetus or the breast-feeding child, but manufacturers generally advise that doctors should avoid prescribing MAOIs to pregnant or breast-feeding mothers);
• in people taking antihistamines and some other drugs (for a full list, please see the British National Formulary).

Drinking alcohol
Drinking alcohol while taking MAOIs may cause you to feel very drowsy. Drinking, even in moderation, can delay your response to antidepressants, so it is best avoided. Also, because of the tyramine reaction, if alcohol is taken with MAOIs, clear spirits such as vodka or gin are safest.

Driving and operating machinery
MAOIs can affect your concentration and reaction times. Therefore, you should not drive or operate machinery if you are drowsy or have other side-effects which may affect your abilities. This includes garden machinery such as lawnmowers and hedge trimmers.

Surgical operations
MAOIs should be reduced gradually, as directed by your doctor, so that you have stopped taking any MAOIs at least two weeks before surgery.