Substituted tryptamines, or simply tryptamines, also known as serotonin analogues (i.e., 5-hydroxytryptamine 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 system, 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 are found in fungi, plants and animals; and sometimes used by humans for the neurological or psychotropic effects of the substance. Prominent examples of tryptamine alkaloids include psilocybin (from "psilocybin mushrooms") and DMT. In South America, dimethyltryptamine is obtained from numerous plant sources, like chacruna, and it is often used in ayahuasca brews. Many synthetic tryptamines have also been made, including the migraine drug sumatriptan, and psychedelic drugs. A 2022 study has found the variety of tryptamines present in wild mushrooms may affect the therapeutic impact.

The tryptamine structure, in particular its indole ring, may be part of the structure of some more complex compounds, for example cyclized tryptamines like LSD, ibogaine, harmaline, mitragynine and yohimbine. A thorough investigation of dozens of tryptamine compounds was published by Alexander Shulgin and Ann Shulgin in 1997 under the title TiHKAL (Tryptamines I Have Known and Loved).

The doses, potencies, durations, and effects of psychedelic tryptamines have been reviewed by Alexander Shulgin and other authors.

The chemical syntheses of numerous tryptamines have been described by Alexander Shulgin in his book TiHKAL (Tryptamines I Have Known and Loved). A well-known and widely used synthetic approach for making tryptamines is the Speeter–Anthony route, which starts with indole. Other tryptamine synthesis routes have also been described, for instance starting with tryptamine rather than indole.

α-Alkyltryptamines are a group of substituted tryptamines which possess an alkyl group, such as a methyl or ethyl group, attached at the alpha carbon, and in most cases no substitution on the amine nitrogen. α-Alkylation of tryptamine makes it much more metabolically stable and resistant to degradation by monoamine oxidase, resulting in increased potency and greatly lengthened half-life. This is analogous to α-methylation of phenethylamine into amphetamine.

Many α-alkyltryptamines are drugs, acting as monoamine releasing agents, non-selective serotonin receptor agonists, and/or monoamine oxidase inhibitors, and produce psychostimulant, entactogen, and/or psychedelic effects. The most well-known of these agents are α-methyltryptamine (αMT) and α-ethyltryptamine (αET), both of which were used clinically as antidepressants for a brief period of time in the past and are abused as recreational drugs. In accordance with its action as a dual releasing agent of serotonin and dopamine, αET has been found to produce serotonergic neurotoxicity similarly to amphetamines like MDMA and PCA, and the same is also likely to hold true for other serotonin and dopamine-releasing α-alkyltryptamines such as αMT, 5-MeO-αMT, and various others.

A number of β-ketotryptamines (beta-ketotryptamines) are known. These compounds are α-alkyl-β-ketotryptamines and are analogous to the cathinones (β-ketoamphetamines) of the related phenethylamine family. Known β-ketotryptamines include BK-NM-AMT, BK-5F-NM-AMT, BK-5Cl-NM-AMT, and BK-5Br-NM-AMT. They act as monoamine releasing agents.