GLP1R and type 2 diabetes mellitus: DPP-4 inhibitors (i.e., alogliptin, linagliptin, saxagliptin, sitagliptin, and vildagliptin), that are able to inhibit the enzyme dipeptidyl peptidase (DPP) IV and lead to increased levels of GLP-1 are drugs that are approved to treat T2DM.