GCG and type 2 diabetes mellitus: At present, there are multiple drugs for the treatment of type 2 diabetes, including traditional sulfonylureas (Stephen et al., 2018), biguanides (Schäfer, 1983), glinides (Chen et al., 2015), thiazolidinediones (Nanjan et al., 2018), α-glucosidase inhibitors (Kazufumi et al., 2014; Patel, 2015), glucagon-like peptide-1 (GLP-1) receptor agonists (Drucker, 2018), dipeptidyl peptidase IV (DPP-4) inhibitors, and sodium-glucose cotransporter 2 (SGLT2) inhibitors (Thornberry and Gallwitz, 2009; Kelly et al., 2019).