Non-selective irreversible MAOI Pregnancy: Do not use in pregnancy, especially during the first and last trimesters, unless there are compelling reasons - there is no evidence of drug safety in human pregnancy nor animal evidence that it is free from hazard, and the effect of psychotropic drugs on the fine brain structure of the foetus is unknown. Contraindicated during lactation, as there is no information on secretion into breast milk. (SPC 4.6)

Isocarboxazid

Isocarboxazid is an irreversible, non-selective monoamine oxidase inhibitor (MAOI) used for depression, generally when other antidepressants have been ineffective.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 30 mg daily, in single or divided doses, until improvement is obtained

Route: Oral

Frequency: Once daily or in divided doses

Max: Up to 60 mg daily - only if no improvement has been seen by 4 weeks, according to the patient's tolerance, for no longer than 4-6 weeks and with close monitoring because of the increased risk of adverse reactions

The maximal effect is only observed after a period varying from 1 to 4 weeks. Once the optimal effect is achieved the dose should be reduced to the lowest amount sufficient to maintain the improvement - clinical experience has shown this to be usually 10-20 mg daily, but up to 40 mg daily may be required in some cases. Elderly: more likely to experience adverse reactions such as agitation, confusion and postural hypotension; half the normal maintenance dose may be sufficient to produce a satisfactory clinical response. Children: not indicated for paediatric use. eMC SPC section 4.2.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Any impairment of hepatic function
Cerebrovascular disorders
Severe cardiovascular disease
Actual or suspected phaeochromocytoma
Hypersensitivity to the active substance or any of the excipients
Combination with SSRIs - serious and sometimes fatal serotonin syndrome reported; start an SSRI only 2 weeks after stopping isocarboxazid, and start isocarboxazid at least a week after stopping an SSRI or related antidepressant (at least 5 weeks for fluoxetine)

Side effects

Orthostatic hypotension, in some patients with disturbances of cardiac rhythm; peripheral oedema
Dizziness, dryness of the mouth, nausea and vomiting, constipation
Blurred vision
Insomnia, drowsiness, weakness and fatigue
Increased appetite and weight gain
Infrequent: headache, sweating, paraesthesiae, peripheral neuritis, hyperreflexia, agitation, overactivity, muscle tremor, confusion, difficulty in micturition, impaired erection and ejaculation, skin rashes; rarely blood dyscrasias (purpura, granulocytopenia)

Interactions

SSRIs and related antidepressants - risk of serious/fatal serotonin syndrome; observe the washout intervals above (SPC 4.3)
Disulfiram - administer with caution; severe toxicity including convulsions and death seen with an MAOI plus disulfiram in rats (US label, Drug Interactions)
Other psychotropic agents - concomitant use generally not recommended because of possible potentiating effects (US label)
MAO inhibitory effects may persist for a substantial period after stopping - allow an interval of 10 days before starting another agent (US label)

Clinical monograph

How it works

It irreversibly inhibits monoamine oxidase, reducing the breakdown of noradrenaline, serotonin and dopamine and thereby increasing their availability in the brain.

Prescribing in practice

Concurrent intake of tyramine-rich foods or interacting sympathomimetic or serotonergic medicines can precipitate a hypertensive crisis or serotonin syndrome, so strict dietary and drug restrictions are essential.
Adequate washout periods are required when switching to or from other antidepressants to avoid dangerous interactions.
Avoid combination with other serotonergic agents, including SSRIs, certain opioids and triptans.

Monitoring

Monitor blood pressure and watch for signs of hypertensive crisis and serotonin syndrome, alongside mood and suicidal ideation.

Counselling the patient

Provide the dietary restriction card and explain which foods and drinks to avoid.
Do not take other medicines, including over-the-counter remedies, without checking for interactions.
Seek urgent help for severe headache, palpitations or neck stiffness.

Evidence & guidelines

Isocarboxazid is an established MAOI reserved for depression unresponsive to other treatments, with well-recognised dietary and drug interactions documented in current prescribing references.

Reference: NICE NG222; Maudsley; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Drugs

Tranylcypromine · Non-selective irreversible MAOI

Pathways