Tetrahydroharmine is a monoamine oxidase inhibitor (MAOI) that occurs naturally in several plants around the world, including banisteriopsis caapi, one of the two main plant ingredients in ayahuasca. Unlike its closely related alkaloids harmine and harmaline, which occur in several other plant species, THH is unique to b. caapi.
THH, while acting as an inhibitor of monoamine oxidase A, is also a seratonin reuptake inhibitor (SRI), which blocks the neurotransmitter serotonin from being recycled in the nervous system and ending its effects. As with all SRIs, this results in an increased concentration and neurotransmission of serotonin.
