4-HO-MET or 4-hydroxy-N-ethyl-N-methyltryptamine, is a novel compound that was first synthesized by the American chemist Alexander Shulgin, who documented it in his 1997 book TiHKAL ("Tryptamines I Have Known and Loved").

4-HO-MET, or 4-hydroxy-N-ethyl-N-methyltryptamine, is a synthetic indole alkaloid molecule of the tryptamine chemical class. Tryptamines share a core structure comprised of a bicyclic indole heterocycle attached at R3 to an amino group via an ethyl side chain. 4-HO-MET is substituted at R4 of its indole heterocycle with a hydroxyl functional group OH−. It also contains a methyl group and an ethyl chain bound to the terminal amine RN of its tryptamine backbone (MET).

This compound pharmacodynamics is believed to come primarily from its activity at the 5-HT2A receptor as a partial agonist. However, the role of these interactions and how they result in psychoactivity remains subject to on-going scientific investigation.