MAOIs and tyramine: the "cheese reaction", and the plate that avoids it

Monoamine oxidase in the gut and liver is your first defence against tyramine, a pressor amine formed by bacterial decarboxylation of tyrosine in aged and fermented foods. Block MAO and dietary tyramine is absorbed intact, dumps noradrenaline from nerve terminals, and blood pressure can spike dangerously. This is the "cheese reaction". When it applies - Irreversible non-selective MAOIs (phenelzine, tranylcypromine, isocarboxazid): full dietary precautions. - Transdermal selegiline at low dose spares gut MAO-A and needs no diet; higher doses do not. - Reversible inhibitors of MAO-A (moclobemide; and the plant harmala alkaloids) are displaceable by tyramine, so the risk is much lower — lower, not zero at high tyramine loads. The foods that matter Highest risk: aged cheeses, cured/fermented meats, soy sauce, miso, yeast extracts (Marmite/Vegemite), sauerkraut, and tap/unpasteurised beer. Fresh cheese, fresh meat and bottled beer are low. It is the aging and the bacteria, not the food group. This is exactly the tier the Temple Plate sets apart from an ordinary nutrition plate — the ferment tier is nutritionally a rounding error and the one tier that can put someone on an MAOI in hospital: https://plate.soapbox.community The other MAOI hazard Serotonergic drugs plus an MAOI is serotonin syndrome, a separate and also life-threatening interaction — see the serotonin-syndrome thread on this board. Mechanism and the neurotransmitter systems: https://wiki.soapbox.community/wiki/Monoamine_Oxidase_Inhibitors_and_Neurotransmitter_Systems Sources: Gillman PK, "Monoamine oxidase inhibitors, opioid analgesics and serotonin toxicity", Br J Anaesth 2005; FDA labelling for phenelzine/tranylcypromine.