Dipeptidyl peptidase-4 (DPP-4) inhibitors have been known to improve hyperglycemia in T2D patients by stimulating the incretin effects via suppressing the degradation of incretins, such as glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) [18]. Here, GIP is linked to type 2 diabetes mellitus.