GCG and type 2 diabetes mellitus: The groups of oral drugs used in T2DM include biguanides, sulfonylureas, α-glucosidase inhibitors, thiazolidinediones, dipeptidyl peptidase IV (DPP-4) inhibitors, glucagonlike-peptide-1 (GLP-1) agonist, sodium-glucose transporter-2 (SGLT-2) inhibitors [1].