Substituted tryptamines, or simply tryptamines, also conceptualizable as serotonin analogues, are organic compounds which may be thought of as being derived from tryptamine itself. The molecular structures of all tryptamines contain an indole ring, joined to an amino (NH₂) group via an ethyl (−CH2–CH2−) sidechain. In substituted tryptamines, the indole ring, sidechain, and/or amino group are modified by substituting another group for one of the hydrogen (H) atoms.

Well-known tryptamines include serotonin, an important neurotransmitter, and melatonin, a hormone involved in regulating the sleep-wake cycle. Tryptamine alkaloids found in fungi, plants and animals are sometimes used by humans and other animals, notably, the jaguar, for their psychotropic effects. Prominent examples of tryptamine alkaloids include psilocybin (from "Psilocybin mushrooms") and DMT (from numerous plant sources, e.g. chacruna, often used in ayahuasca brews). Many synthetic tryptamines have also been made, including the migraine drug sumatriptan and its relatives, and psychedelic drugs.