4-Methoxytryptamine (4-MeO-T; developmental code name PAL-548) is a serotonin receptor modulator of the tryptamine and 4-hydroxytryptamine families. It is the O-methyl derivative of 4-hydroxytryptamine (4-HT) and a positional isomer of 5-methoxytryptamine and 6-methoxytryptamine.
The drug has been found to act as a potent serotonin 5-HT<sub>2A</sub> receptor full agonist, with an of 9.02nM and an of 108%. It was inactive as a monoamine releasing agent, including of serotonin, norepinephrine, and dopamine, in rat brain synaptosomes (all = >10,000nM), but was a very low-potency serotonin reuptake inhibitor ( = 4,114nM).
4-Methoxytryptamine was first described in the scientific literature by at least 1962.