Tetrahydroharmine

Tetrahydroharmine, also known as 7-methoxy-1,2,3,4-tetrahydroharman, is a fluorescent indole alkaloid and β-carboline that occurs in the tropical liana species Banisteriopsis caapi.

Use and effects

THH has been reported to produce psychoactive effects similar to those of harmaline in humans. It has been reported to be about one-third as potent as harmaline at a dose of 300mg orally. THH is believed to be one of the constituents of Banisteriopsis caapi responsible for the hallucinogenic effects of the plant. The duration of THH is unknown.

THH, like other harmala alkaloids in B. caapi, namely harmaline and harmine, is a reversible inhibitor of monoamine oxidase A, but it also inhibits the reuptake of serotonin. THH contributes to B. caapi's psychoactivity as a serotonin reuptake inhibitor. In contrast to other β-carbolines, THH shows minimal affinity for the serotonin 5-HT_2A receptor -THH, K_i = 5,890nM for S. Similarly, THH shows negligible affinity for the serotonin 5-HT_1A and 5-HT_2C receptors and the dopamine D₂ receptor.

The elimination half-life of tetrahydroharmine is 4.7 to 8.8hours.

The chemical synthesis of tetrahydroharmine has been described.

Harmala alkaloids are considered Schedule 9 prohibited substances under the Poisons Standard. A Schedule 9 substance is a substance which may be abused or misused, the manufacture, possession, sale or use of which should be prohibited by law except when required for medical or scientific research, or for analytical, teaching or training purposes with approval of Commonwealth and/or State or Territory Health Authorities.

THH is not a controlled substance in Canada as of 2025.