By sustained inhibiting dipeptidyl peptidase 4 (DPP4), the enzyme degrading GLP-1 in the blood, this class of drug elevates blood active GLP-1 level by around 1-fold and effectively lowers HbA1c of T2D by 0.6–0.8% (Herman et al., 2006; Esposito et al., 2015). Here, GLP1R is linked to type 2 diabetes mellitus.