GCG and type 2 diabetes mellitus: The oral therapies that are currently widely used for the treatment of patients with T2DM act mainly by reducing HGP (e.g., biguanides), promoting insulin action (e.g., thiazolidinediones), stimulating insulin release (e.g., sulfonylurea drugs), inhibiting the absorption of intestinal glucose (e.g., α-glucosidase inhibitors), and increasing the endogenous glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) levels (e.g., sitagliptin and saxagliptin) [3].