In the pharmacotherapy of T2DM, beside insulin, there are many other classes of drugs that have received approval for use: biguanides, sulphonylureas, glinides, thiazolidindiones, alpha-glucosidase inhibitors, dipeptidyl peptidase-4 (DPP-4) inhibitors, glucagon-like peptide 1 (GLP-1) analogs/GLP-1 receptor agonists, sodium-glucose–linked transporter 2 (SGLT-2) inhibitors [91], and recently approved, dual gastric inhibitory polypeptide (GIP)/GLP-1 receptor agonist [92]. Here, DPP4 is linked to type 2 diabetes mellitus.