CTW0415 is an experimental drug from the piperidine family, which acts as a selective positive allosteric modulator of the 5-HT<sub>2C</sub> receptor, with higher potency than older drugs such as VA012. Structure-activity relationship studies showed that small variations to chain length and side chain substitution could lead to preferential binding for either 5-HT<sub>2C</sub> or the related 5-HT<sub>2A</sub> receptor, which subsequently led to the discovery of the related 5-HT<sub>2A</sub> selective positive allosteric modulator CTW0404.