The amine group of tryptamine possesses a nitrogen with two hydrogens where functional groups can be substituted. Let’s start with the simple case where both of these substitutions are identical. The best known example is dimethyltryptamine, abbreviated as DMT (D for di meaning two, M for the methyl alkyl substitions, and T for the tryptamine backbone). There are other tryptamines like DMT with longer symmetrical alkyl chains which have similar effects and are named in a similar manner.
DMT is typically smoked as other consumption routes are ineffective due to MAO degradation, but the longer alkyl chains do not have this issue and are all orally active. There is no theoretical limit to the alkyl chain length, but potency decreases as chain length increases. DBT is the longest simple chain dialkylated tryptamine commonly bioassayed in man.
We can also consider asymmetrical cases where the two substitutions are different. The possible combinations quickly increase in number as the following table up to alkyl chains of three carbons in size illustrates. Asymmetric compounds are referred to by giving initials to both of their substitutions (shortest chain first) and ending with a T to signify the tryptamine backbone.
Linked compounds have a full entry in TiHKAL.
These two rulesets for symmetric and asymmetric substitutions allow us to refer to a huge variety of n-alkylated tryptamines using abbreviations in a simple and consistent manner.
Shulgin, A. #2 DBT. Tryptamines I Have Known and Loved. Transform Press, 1997.