2C-T-21.5 is a lesser-known psychedelic drug related to compounds such as 2C-T-21 and 2C-T-28. It was originally named by Alexander Shulgin and discussed in his book PiHKAL,[1] but was not synthesised at that time. 2C-T-21.5 was ultimately synthesised and tested by Daniel Trachsel some years later. It has a binding affinity of 146 nM at 5-HT2A and 55 nM at 5-HT2C. It produces typical psychedelic effects, being slightly less potent but somewhat longer acting than 2C-T-2 or 2C-T-21,[2][3][4] with an active dose of 12–30 mg, and a duration of action of 8–14 hours. Unlike 2C-T-21 it will not form the highly toxic fluoroacetate as a metabolite, instead producing the less toxic difluoroacetic acid.[5][6]
^Trachsel D, Lehmann D, Enzensperger C (2013). Phenethylamine: Von der Struktur zur Funktion. Nachtschatten Verlag AG. pp. 789–791. ISBN978-3-03788-700-4.
^WO 2023/156450, Nivorozhkin A, Hartsel JA, Canal CE, Salituro FG, Mueller TA, Greene BJ, Belser A, Avery KL, Reichelt AC, Varty GB, Palfreyman M, "Therapeutic phenethylamine compositions and methods of use.", published 24 August 2023, assigned to Cybin Irl Ltd.