6-Hydroxytryptamine (6-HT or 6-HO-T) is a serotonin receptor modulator of the tryptamine family related to serotonin. It is a positional isomer of serotonin (5-hydroxytryptamine; 5-HT) and of 4-hydroxytryptamine (4-HT).
6-Hydroxytryptamine shows dramatically reduced affinity for serotonin receptors, including the serotonin 5-HT<sub>1A</sub>, 5-HT<sub>1B</sub>, 5-HT<sub>2A</sub>, and 5-HT<sub>2C</sub> receptors (K<sub>i</sub> = 1,590nM, 5,890nM, 11,500nM, and 5,500nM, respectively), compared to serotonin, 4-hydroxytryptamine, 5-methoxytryptamine, and certain other tryptamines. It did not produce hyperlocomotion in rodents but did partially reverse reserpine-induced hypoactivity. 6-Hydroxytryptamine appears to be less susceptible to metabolism by monoamine oxidase (MAO) than serotonin.
6-Hydroxytryptamine was first described in the scientific literature by the 1950s.
Certain ò-carbolines and harmala alkaloids, such as harmol, harmalol, and tetrahydroharmol, as well as their O-methyl (methoxy) analogues including harmine, harmaline, and tetrahydroharmine, are notable in being naturally occurring cyclized tryptamine derivatives of 6-hydroxytryptamine. The same is true of certain iboga alkaloids, such as tabernanthine and ibogaline. Tabernanthalog (DLX-007) is a synthetic simplified ibogalog analogue of tabernanthine that is under development for use as a potential pharmaceutical drug in the treatment of neuropsychiatric disorders.