MPEP is a potent and selective antagonist of the metabotropic glutamate receptor 5 (mGlu5), demonstrating an IC50 of 36 nM. It shows negligible activity at other mGlu receptor subtypes (mGlu1b/2/3/4a/7b/8a/6). This compound is widely used in neuroscience research to investigate mGlu5 function in vitro and in animal models of neurological disorders.