G protein-coupled receptors (GPCRs) regulate nearly every physiological process in mammals and serve as targets for more than 30% of drugs. Allosteric modulators of GPCRs have attracted considerable attention due to their unique pharmacological advantages: they can preserve the signal transduction characteristics of endogenous ligands, reduce side effects, expand the range of signal transduction, and even restore the function of pathogenic mutant receptors. However, the development of allosteric modulators targeting GPCRs faces significant bottlenecks. To date, only two well-known GPCR allosteric modulators have entered clinical trials: emraclidine, which targets the M4 receptor for the treatment of schizophrenia, and SBI-553, which targets NTSR1 to mitigate addiction. The slow progress in developing GPCR allosteric modulators for therapeutic use is mainly attributed to the lack of systematic screening and pharmacological characterization methods, as well as the gap in understanding the molecular mechanisms of allosteric regulation.