Pirenperone

Pirenperone (INN, USAN, BAN; developmental code names R-47456, R-50656) is a serotonin receptor antagonist described as an antipsychotic and tranquilizer which was never marketed. It is a relatively selective antagonist of the serotonin 5-HT2 receptors and has been used in scientific research to study the serotonin system. In the 1980s, the drug was found to block the effects of the lysergic acid diethylamide (LSD) in animals, and along with ketanserin, led to the elucidation of the 5-HT2A receptor as the biological mediator of the effects of serotonergic psychedelics.