Mental health
MAOIs (monoamine oxidase inhibitors)
An older class of antidepressant — Effective older antidepressants reserved for resistant cases because of strict food and drug restrictions.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is MAOIs (monoamine oxidase inhibitors)?
MAOIs are an older class of antidepressant that can be very effective, including in depression that has not responded to other treatments. They are now used mainly by specialists because they require strict food and medicine restrictions for safety.
- How it works: They block monoamine oxidase, the enzyme that breaks down the mood-related brain chemicals serotonin, noradrenaline and dopamine, so more of these remain available — lifting mood.
- In practice: In practice the older, non-selective MAOIs are effective antidepressants — sometimes when others have failed, and in certain anxiety and atypical depression — but they are now used rarely and by specialists because of two serious interaction hazards that require strict rules.
What it is
MAOIs are an older class of antidepressant that can be very effective, including in depression that has not responded to other treatments. They are now used mainly by specialists because they require strict food and medicine restrictions for safety.
How it works
They block monoamine oxidase, the enzyme that breaks down the mood-related brain chemicals serotonin, noradrenaline and dopamine, so more of these remain available — lifting mood. The same blocked enzyme normally also disposes of tyramine from food and limits serotonin build-up, which is why certain foods and drugs become dangerous.
In practice
In practice the older, non-selective MAOIs are effective antidepressants — sometimes when others have failed, and in certain anxiety and atypical depression — but they are now used rarely and by specialists because of two serious interaction hazards that require strict rules. First, the "cheese reaction": MAOIs let tyramine (in matured cheeses, cured/fermented meats, some draught beers, yeast extracts and other aged foods) build up and trigger a dangerous surge in blood pressure (a hypertensive crisis with severe headache), so a tyramine-restricted diet is essential. Second, serotonin toxicity: combining them with many other antidepressants, certain opioids, some cough and cold remedies (and several other drugs) can cause life-threatening serotonin syndrome, so generous washout gaps are left when switching to or from them. Because of these, people carry clear written guidance, and any new medicine — prescription or over-the-counter — is checked first. A skin-patch form of one MAOI and the reversible MAOI moclobemide carry fewer dietary restrictions but still need care. They are started and stopped carefully and never combined casually with other serotonergic drugs.
Examples
Practical use
How to take it & use it well
- Take it regularly as prescribed and do not stop suddenly, as these medicines need to be reduced gradually under your doctor's guidance.
- Follow the food advice carefully, avoiding aged cheeses, cured or fermented meats, yeast extract spreads and some draught beers, as these can cause a dangerous surge in blood pressure known as the cheese reaction.
- Check with a pharmacist before taking any new medicine, including cough, cold and decongestant remedies, as many ordinary products can interact dangerously with these antidepressants.
- Carry a card or note saying you take this type of medicine, so that anyone treating you in an emergency knows to avoid certain drugs.
- Seek urgent help for a sudden severe and pounding headache, especially with a stiff neck, chest pain or palpitations, as this can be a sign of a blood-pressure surge.
- When switching to or from another antidepressant, follow the washout gap your doctor sets exactly, as overlapping them can cause a serious reaction.
Common uses
- Treatment-resistant depression
- Atypical depression and some anxiety disorders
- Specialist use when other antidepressants have not worked
Monitoring
- Mood and response; blood pressure
- Strict adherence to dietary and drug restrictions
- Safe washout periods when starting or stopping
Weighing it up
Advantages & disadvantages
Advantages
- They can be very effective for some types of depression, including cases that have not responded to other treatments.
- They can help particular patterns of depression, such as those with strong anxiety or unusual features.
- There is long experience with them, so their benefits and risks are well understood.
- For the right person, under careful supervision, they can work when several other options have failed.
- A skin-patch form of one of them can reduce the food restrictions at lower strengths, under specialist advice.
Disadvantages
- They require strict avoidance of certain foods to prevent a dangerous rise in blood pressure.
- They interact with many medicines, including common cold and pain remedies, so every new product must be checked.
- Switching to or from other antidepressants needs a careful washout gap to avoid serious reactions.
- Side effects can include dizziness on standing, sleep changes, weight changes and a dry mouth.
- Because of these restrictions, they are usually reserved for when other treatments have not worked.
Key safety principles
What to watch for
- Tyramine ("cheese") reaction — aged cheeses, cured/fermented foods, some beers and yeast extracts can cause a dangerous blood-pressure surge; follow the diet strictly.
- Serotonin syndrome risk — must not be combined with many other antidepressants, certain opioids and some cold remedies; leave the advised washout gaps when switching.
- Always check any new medicine (including over-the-counter) first; carry the written food and drug guidance.
Key interactions
What to avoid or check alongside
- Aged cheeses, cured or fermented meats, yeast extract spreads, soy products and some draught beers contain tyramine, which can cause a dangerous blood-pressure surge.
- Combining them with other antidepressants, or starting one too soon after another, can cause a serious reaction known as serotonin syndrome.
- Certain strong painkillers and some cough and cold remedies, including decongestants, can interact dangerously and must be avoided.
- Some migraine treatments and herbal products such as St John's wort can also trigger a serious reaction.
- Always tell every doctor, dentist and pharmacist that you take this type of medicine before anything new is given.
Patient & carer advice
- Follow the food list carefully — some cheeses, cured meats, yeast extracts and beers can dangerously raise your blood pressure
- Never take a new medicine, including from a pharmacy or supermarket, without checking it is safe with this one
- Seek urgent help for a sudden severe (often throbbing) headache
Use with
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Answers
MAOIs (monoamine oxidase inhibitors): frequently asked questions
What is the cheese reaction?
It is a dangerous surge in blood pressure that can happen when these antidepressants are combined with foods high in a substance called tyramine, such as aged cheese, cured meats and yeast extract. Warning signs include a sudden severe pounding headache, and it needs urgent medical attention. Following the food advice prevents it.
Which foods do I need to avoid?
The main ones are aged or mature cheeses, cured and fermented meats, yeast extract spreads, soy sauce and some draught or unpasteurised beers. Your team will give you a full list. Fresh foods are generally fine, so the diet is manageable once you know what to watch for.
Can I take cold and flu remedies with an MAOI?
Not without checking first. Many over-the-counter cough, cold and decongestant products can interact dangerously with these medicines and raise your blood pressure sharply. Always ask a pharmacist before buying anything, and mention your medicine whenever you are prescribed something new.
Why do I need a gap when switching antidepressants?
These medicines stay active in the body for a while, so starting another antidepressant too soon, or starting an MAOI too soon after stopping one, can cause a serious reaction called serotonin syndrome. Your doctor will set a washout gap, and it is important to follow it exactly.
What should I do if I get a sudden severe headache?
A sudden, severe, pounding headache, especially with a stiff neck, chest pain, palpitations or feeling sick, can be a sign of a blood-pressure surge and needs urgent help. Treat it as an emergency rather than waiting for it to pass.
Authoritative sources
Always verify against the source
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