GLP1R and type 2 diabetes mellitus: Recently, GLP-1-based drugs, including GLP-1 analogues and dipeptidyl peptidase-IV (DPP-IV) inhibitors that inhibit breakdown of GLP-1, have been developed for treating T2D (9–11), but patients given GLP-1-based drugs suffer from side effects such as nausea and vomiting (12).