SCH 202676 is a reversible inhibitor of both agonist and antagonist binding to diverse G protein-coupled receptors (GPCRs). It blocks the binding of radiolabeled ligands to human opioid, adrenergic, muscarinic, dopaminergic, adenosine, and purinergic receptors. It displays IC50 values of 0.1 to 1.8 μM for modulating ligand binding. SCH 202676 may modulate GPCRs via thiol modification.