Provided are a novel class A GPCR antagonist, a production method for same, and a novel compound which interacts with the binding site of a class A GPCR Na+- water molecule cluster. A compound, or a salt thereof, having a structure in which are bonded a class A GPCR-binding compound and a functional group that binds to a class A GPCR Na+- water molecule cluster binding site. A class A GPCR antagonist production method comprising a step for binding, to another compound, a compound that binds to a class A GPCR Na+- water molecule cluster binding site.