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_2A receptor full agonist, with an EC₅₀Tooltip half-maximal effective concentration of 9.02 nM and an E_maxTooltip half-maximal effective concentration of 108%. It was inactive as a monoamine releasing agent, including of serotonin, norepinephrine, and dopamine, in rat brain synaptosomes (all EC₅₀ = >10,000 nM), but was a very low-potency serotonin reuptake inhibitor (IC₅₀Tooltip half-maximal effective concentration = 4,114 nM).

4-Methoxytryptamine was first described in the scientific literature by at least 1962.