SB-204741 is a drug which acts as a potent and selective antagonist at the serotonin 5-HT<sub>2B</sub> receptor, with around 135x selectivity over the closely related 5-HT<sub>2C</sub> receptor, and even higher over the 5-HT<sub>2A</sub> receptor and other targets. It is used in scientific research for investigating the functions of the 5-HT<sub>2B</sub> receptor.