An MAOI antidepressant
Isocarboxazid
An older MAOI antidepressant reserved for resistant depression, needing a strict low-tyramine diet.
What is Isocarboxazid?
Isocarboxazid is a monoamine oxidase inhibitor (MAOI), an older antidepressant usually started by a specialist for depression that has not responded to other treatments. Like the other irreversible MAOIs it needs a strict low-tyramine diet — avoiding mature cheese, cured meats and yeast extracts — to prevent a dangerous rise in blood pressure, warned of by a sudden severe throbbing headache. It also interacts dangerously with many medicines, including other antidepressants, certain painkillers and decongestants.
Education and reference only. This is a plain-language guide to Isocarboxazid — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Isocarboxazid is one of the original antidepressants, a monoamine oxidase inhibitor (MAOI). In current UK practice it is usually a specialist choice reserved for depression that has not responded to newer antidepressants. Like the other irreversible MAOIs, it can be effective but requires strict attention to diet and to other medicines because of the risk of serious interactions.
How it works
Isocarboxazid blocks monoamine oxidase, the enzyme that breaks down mood-related brain chemicals such as serotonin, noradrenaline and dopamine, leaving more of them available to lift mood over weeks. Because the same enzyme breaks down tyramine from food and the active parts of some medicines, these must be restricted to prevent a dangerous build-up and a surge in blood pressure.
Company & origin
Originated / developed by: Generic (long-established).
An older MAOI antidepressant used in the UK for depression that has not responded to other treatments.
What it treats
Conditions Isocarboxazid is used for
Practical use
How to take Isocarboxazid
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Follow the low-tyramine diet carefully, avoiding mature cheese, cured or aged meats, yeast extracts and other listed foods.
- Take it regularly as prescribed and allow a few weeks for the full benefit.
- Do not take other medicines, including over-the-counter cold, flu or decongestant remedies, without checking they are safe with an MAOI.
- Carry an MAOI warning card and tell any doctor, dentist or pharmacist that you take isocarboxazid; precautions continue for weeks after stopping.
- If you miss a dose, take it when you remember unless it is nearly time for the next, then skip it — do not double up, and do not stop suddenly.
Weighing it up
Advantages & disadvantages of Isocarboxazid
Advantages
- Can be effective for depression that has not responded to other antidepressants.
- An established specialist option when other treatments have failed.
- Works through a different mechanism from newer antidepressants.
Disadvantages
- Requires a strict low-tyramine diet to avoid dangerous blood-pressure surges.
- Interacts dangerously with many medicines, including other antidepressants and decongestants.
- Precautions continue for weeks after stopping, and a washout is needed before switching.
Practical use
Good to know
A strict low-tyramine diet is essential: avoid mature and aged cheeses, cured, smoked or aged meats, yeast and meat extracts (such as Marmite, Bovril and OXO), some fermented foods and certain drinks. Eating these can cause a dangerous rise in blood pressure (a hypertensive crisis); a sudden, severe, throbbing headache, often with a stiff neck, sweating or palpitations, is an emergency. It interacts dangerously with many medicines, including other antidepressants, some painkillers (especially pethidine), and decongestants and stimulants in cold and flu remedies. The precautions continue for a couple of weeks after stopping, a washout is needed before starting or switching to another antidepressant, and it should never be stopped abruptly. Carry an MAOI warning card and tell any health professional you take an MAOI.
Who should not take it / use with caution
- It must not be combined with other antidepressants, certain painkillers such as pethidine, or decongestants and similar stimulant medicines.
- People with phaeochromocytoma, significant liver disease, or certain heart and circulation problems should not take it.
- Anyone unable to follow the dietary and medicine restrictions, or with a history of serious MAOI reactions, should avoid it.
Monitoring
- Blood pressure is checked, and you are taught to recognise the warning signs of a hypertensive crisis.
- Mood and any thoughts of self-harm are reviewed, especially early in treatment.
- Adherence to the diet and medicine restrictions is reviewed at appointments.
Side effects
- Dizziness (especially on standing), drowsiness or insomnia, dry mouth and constipation.
- Weight changes, swelling of the ankles and difficulty passing urine.
- Dangerously, a hypertensive crisis from tyramine — a sudden severe throbbing headache needs emergency care.
Key interactions
- Other antidepressants (including SSRIs and tricyclics) must be avoided, with a washout when switching.
- Some painkillers, especially pethidine, and decongestants or stimulants can cause severe reactions.
- Many cold and flu remedies and certain foods interact, so always check before taking anything new.
Available as: Tablets taken by mouth.
Answers
Isocarboxazid: frequently asked questions
Why must I avoid certain foods?
Isocarboxazid blocks the enzyme that breaks down tyramine, so high-tyramine foods like mature cheese and cured meats can cause a dangerous rise in blood pressure.
What are the warning signs of a serious reaction?
A sudden, severe throbbing headache, often with a stiff neck, sweating or palpitations, can signal a hypertensive crisis and needs emergency help.
Can I take cold and flu remedies?
Not without checking, as many contain decongestants that can react dangerously with isocarboxazid; always ask a pharmacist first.
How long do precautions last after stopping?
The effect lingers for a couple of weeks, so the diet and medicine precautions, and a washout before switching, are still needed after you stop.
Can I switch straight to another antidepressant?
No, a washout period is needed before starting most other antidepressants, because combining them too soon can be dangerous.
The wider class
About MAOI antidepressants
Isocarboxazid belongs to the maoi antidepressants class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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