MAOI tyramine reaction — MRCPsych Paper A MCQ

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EasyPsychopharmacologyMAOI tyramine reactionMRCPsych Paper A

A 36-year-old woman taking phenelzine develops a severe headache, palpitations and marked hypertension shortly after eating mature cheese. Which mechanism best explains this reaction?

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Correct answer: E — MAO inhibition reducing tyramine metabolism and increasing noradrenaline release

Phenelzine is an irreversible, non-selective monoamine oxidase inhibitor. Inhibition of intestinal and hepatic MAO reduces the first-pass metabolism of dietary tyramine. Tyramine therefore reaches the systemic circulation and acts as an indirect sympathomimetic, promoting noradrenaline release from sympathetic nerve terminals. The resulting adrenergic surge causes the characteristic severe headache, palpitations and marked hypertension—the MAOI–tyramine or “cheese” reaction. Alpha-2 antagonism can also enhance noradrenergic transmission but is not phenelzine’s mechanism and does not explain the dietary trigger. SERT inhibition would raise concern for serotonin toxicity, usually with mental-state and neuromuscular abnormalities such as agitation and clonus. GABA-A modulation and muscarinic blockade do not explain this hypertensive reaction.

Reference: Royal College of Psychiatrists, Use of monoamine oxidase inhibitors (MAOIs) in psychiatric practice, Dietary restrictions section, July 2020. https://www.rcpsych.ac.uk/docs/default-source/improving-care/better-mh-policy/position-statements/ps03_20.pdf