RS-102221 is a drug developed by HoffmannâÂÂLa Roche, which was one of the first compounds discovered that acts as a potent and selective antagonist at the serotonin 5-HT<sub>2C</sub> receptor, with around 100àselectivity over the closely related 5-HT<sub>2A</sub> and 5-HT<sub>2B</sub> receptors. It has anxiolytic effects in animal studies, increases the effectiveness of SSRI antidepressants, and shows a complex interaction with cocaine, increasing some effects but decreasing others, reflecting a role for the 5-HT<sub>2C</sub> receptor in regulation of the dopamine signalling system in the brain.