Chemistry
Harmala alkaloids are MAO-inhibiting beta-carbolines. The three most studied harmala alkaloids in the B. caapi vine are harmine, harmaline and tetrahydroharmine. Harmine and harmaline are selective and reversible inhibitors of monoamine oxidase A (MAO-A), while tetrahydroharmine is a weak serotonin reuptake inhibitor (SRI). This inhibition of MAO-A allows DMT to diffuse unmetabolized past the membranes in the stomach and small intestine, and eventually cross the blood–brain barrier (which, by itself, requires no MAO-A inhibition) to activate receptor sites in the brain. Without RIMAs or the MAOI of MAO-A, DMT would be oxidised (and thus rendered biologically inactive) by monoamine oxidase enzymes in the digestive tract.
Individual polymorphisms in the cytochrome P450-2D6 enzyme affect the ability of individuals to metabolize harmine. Some natural tolerance to habitual use of ayahuasca (roughly once weekly) may develop through upregulation of the serotonergic system. A phase 1 pharmacokinetic study on ayahuasca (as Hoasca) with 15 volunteers was conducted in 1993, during the Hoasca Project. A review of the Hoasca Project has been published.
Read more about this topic: Ayahuasca
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