MAOI (Irreversible Monoamine Oxidase Inhibitor) Pregnancy: §4.6: do not use during pregnancy, especially during the first and last trimesters, unless there are compelling reasons. There is no evidence as to drug safety in human pregnancy, nor evidence from animal work that it is free from hazard. Breastfeeding: it is not known if phenelzine is excreted in breast milk — because of the potential for serious adverse effects to the infant, a decision should be made whether to discontinue the drug or not to breast-feed.

Phenelzine

Brand names: Nardil

Phenelzine is a non-selective, irreversible monoamine oxidase inhibitor (MAOI) used in the treatment of depression, including atypical and treatment-resistant cases.

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: One 15 mg tablet three times a day

Route: Oral

Frequency: Three times a day

Max: If no response is evident after two weeks the dosage may be increased to a maximum of one 15 mg tablet four times a day. Doses of up to two 15 mg tablets three times a day may be used in hospitals.

Source: UK SPC (eMC) for Nardil 15 mg film-coated tablets, §4.2 (https://www.medicines.org.uk/emc/product/228/smpc). ADULTS: one 15 mg tablet three times a day; a response is usually seen within the first week; if no response is evident after two weeks the dosage may be increased to a maximum of one 15 mg tablet four times a day; doses of up to two 15 mg tablets three times a day may be used in hospitals. The effectiveness of the drug may not become apparent in less than 4 weeks of therapy. After a satisfactory response has been achieved the dosage may be reduced very gradually to a suitable maintenance level, which may be as low as one 15 mg tablet every other day. ELDERLY (over 65 years): as for adults; postural hypotension may be an unwanted effect of MAOIs in the elderly; elderly patients tend to receive multiple drug therapies so the possibility of increased risk of drug interactions should be borne in mind — this medicine should only be used with great caution in elderly patients. Despite these problems, MAOIs (including phenelzine) have been found to be useful in the treatment of depression in the elderly. PAEDIATRIC (not expressed as a per-kg dose in the SPC): this medicine is NOT indicated for children under 16 years of age. Verify any under-18 use against a children's formulary. WITHDRAWAL/SURGERY (§4.4): abrupt withdrawal should be avoided where possible because of the possibility of a withdrawal syndrome; phenelzine should be withdrawn two weeks before elective surgery/dentistry. Use only with great caution in agitated patients or those with cardiovascular disease, epilepsy, blood dyscrasias, porphyria or diabetes, and in patients taking diuretics; observe blood pressure frequently to detect any pressor response and discontinue therapy if palpitations or frequent headaches occur; follow closely for postural hypotension. METHOD OF ADMINISTRATION: oral administration. NOTE: the retrieved §4.5 text is TRUNCATED at the source-fetch limit — the dietary restriction list is incomplete; verify the full §4.5 (tyramine-containing foods and drug interactions) before prescribing.

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

Hypersensitivity to the active substance or to any of the excipients
Phaeochromocytoma
Cerebrovascular disease
Congestive heart failure
A history of liver disease, or abnormal liver function tests
Combination with other MAOIs, 5HT1 agonists, dibenzazepine derivative drugs or other antidepressants
Combination with guanethidine, dextromethorphan, or with CNS depressants such as alcohol and narcotic analgesics — death has been reported in patients receiving a single dose of pethidine
Patients taking phenelzine should not undergo elective surgery
Not indicated in the manic phase

Side effects

Hypertensive crises are the most important reaction associated with phenelzine — associated with intracranial bleeding and sometimes fatal (frequency of hypertension: unknown); common orthostatic hypotension
Common: dizziness, drowsiness, hyperreflexia, myoclonic jerks; uncommon headache, paraesthesia, seizure, peripheral neuropathy
Common: insomnia, anorgasmia; uncommon nervousness, euphoric mood, behavioural disorder, confusional state, hallucinations; suicidal ideation and suicidal behaviour (frequency unknown)
Common: nausea, vomiting, dry mouth, constipation; common oedema, asthenia, fatigue; common blurred vision
Common: serum transaminase increased; uncommon elevated liver enzymes, weight increased, arrhythmia; very rare fatal progressive necrotising hepatocellular damage and neuroleptic malignant syndrome (occasionally fatal)

Interactions

Other MAOIs, 5HT1 agonists, dibenzazepine derivative drugs and other antidepressants — must not be combined
Pethidine and other narcotic analgesics, and CNS depressants including alcohol — must not be combined; death has been reported after a single dose of pethidine
Guanethidine and dextromethorphan — must not be combined
Self-medication, particularly cold cures, cough cures, hay fever medications, anti-appetite medicines, weight reducing preparations and 'pep' pills — patients should be warned against these
Food interactions: patients should avoid high protein food that has undergone breakdown by aging, fermentation, pickling, smoking or bacterial contamination, and should avoid cooked or plain cheese and Oxo (the retrieved §4.5 food list is truncated at the source-fetch limit — verify the complete list)
Elective surgery/dentistry — phenelzine should be withdrawn two weeks beforehand; concurrent electroconvulsive therapy requires caution

Clinical monograph

How it works

It irreversibly inhibits monoamine oxidase, increasing central availability of serotonin, noradrenaline and dopamine; restoration of enzyme activity requires synthesis of new monoamine oxidase.

Prescribing in practice

Patients must avoid tyramine-rich foods and sympathomimetic or serotonergic drugs because of the risk of severe hypertensive crisis (the 'cheese reaction') and serotonin syndrome.
Adequate washout periods are required when switching to or from other antidepressants, including a longer interval after stopping fluoxetine.
Postural hypotension, insomnia and hepatotoxicity may occur, and abrupt withdrawal should be avoided.

Monitoring

Monitor blood pressure, mental state and liver function, and remain alert for signs of hypertensive crisis or serotonin toxicity.

Counselling the patient

You will be given a list of foods and medicines to avoid, including mature cheese, cured meats and yeast extracts; follow it carefully.
Tell any healthcare professional or pharmacist that you take a MAOI before starting any new medicine, including over-the-counter remedies.
Seek urgent help if you develop a severe throbbing headache, palpitations or chest pain.

Evidence & guidelines

The dietary and drug interaction precautions for irreversible MAOIs such as phenelzine are well established and reinforced by MHRA and SPC guidance.

Reference: Maudsley Prescribing Guidelines (13th Ed); 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.

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Pathways