6-MeO-THH, also known as 6-methoxy-1,2,3,4-tetrahydroharman, is a ò-carboline (or more specifically a pinoline) derivative and a structural isomer of tetrahydroharmine (7-MeO-THH). It is mentioned in Alexander Shulgin's book TiHKAL (Tryptamines I Have Known and Loved), stating that 6-MeO-THH is very similar to the other carbolines. The compound has been isolated from certain plants of the Virola family.
6-MeO-THH is reported to be hallucinogenic similarly to other ò-carbolines like harmaline. Limited testing suggests that it possesses mild psychoactive effects at a dose of 1.5mg/kg (~100mg for a 70-kg person) orally and is said to be about one-third as potent as 6-methoxyharmalan and three times as potent as harmaline. Its dose range and duration are unknown.
Very little is known about the psychoactivity of 6-MeO-THH in humans. Studies in rats have shown it to bind to a number of serotonin 5-HT<sub>1</sub> receptors and 5-HT<sub>2</sub> receptors, dopamine D<sub>2</sub> receptors, benzodiazepine receptors, and imidazoline receptors.
The chemical synthesis of 6-MeO-THH has been described.
6-MeO-THH is not a controlled substance in Canada as of 2025.