PSB-SB-487 is an experimental drug which is used as a pharmacological research tool. It is a coumarin derivative which is an antagonist at the former orphan receptorGPR55. Unlike older GPR55 antagonists such as O-1918, PSB-SB-487 has good selectivity over the related receptor GPR18, with an IC50 of 113nM at GPR55 vs 12500nM at GPR18.[1] However it has poorer selectivity over other related receptors, acting as a weak antagonist at CB1 with a Ki of 1170nM, and a partial agonist at CB2 with a Ki of 292nM.[2]