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 receptor GPR55. Unlike older GPR55 antagonists such as O-1918, PSB-SB-487 has good selectivity over the related receptor GPR18, with an IC<sub>50</sub> of 113nM at GPR55 vs 12500nM at GPR18. However it has poorer selectivity over other related receptors, acting as a weak antagonist at CB<sub>1</sub> with a Ki of 1170nM, and a partial agonist at CB<sub>2</sub> with a Ki of 292nM.