Harmala alkaloids as reversible MAO-A inhibitors — what "reversible" changes

The beta-carboline alkaloids of Peganum harmala (Syrian rue) and Banisteriopsis caapi — harmine, harmaline, tetrahydroharmine — are reversible inhibitors of MAO-A (RIMAs). "Reversible" is the whole story of how they behave and where the danger is. Why reversibility matters An irreversible MAOI (phenelzine) destroys the enzyme; recovery needs new enzyme synthesis over ~2 weeks. A reversible inhibitor sits on the enzyme and can be displaced. For dietary tyramine this is protective — a large tyramine load can outcompete the inhibitor — so the tyramine (cheese) reaction risk is lower with RIMAs than with irreversible MAOIs. Lower, not absent. The interaction that is NOT forgiving Reversibility does nothing to protect against serotonin toxicity. Harmala alkaloids + any serotonergic drug (SSRIs, SNRIs, tramadol, MDMA, dextromethorphan, St John's wort) is a serotonin-syndrome risk, and this is the mechanism behind the serious ayahuasca drug-interaction warnings. The classic preparation also pairs the MAO-A inhibition with an oral tryptamine (DMT) that MAO would otherwise destroy — which is the entire point of the combination and also where its acute risk lives. Pharmacokinetics Tetrahydroharmine additionally has SERT (serotonin reuptake) activity of its own, so the plant mix is not a pure MAOI. Mechanism and the neurotransmitter map: https://wiki.soapbox.community/wiki/Monoamine_Oxidase_Inhibitors_and_Neurotransmitter_Systems The oral-DMT / metabolic-redirection logic: https://wiki.soapbox.community/wiki/Oilahuasca Sources: Callaway JC et al., "Pharmacokinetics of Hoasca alkaloids in healthy humans", J Ethnopharmacol 1999; Gillman PK on serotonin toxicity.