Oral drugs used to treat type 2 diabetes mellitus (T2DM) are divided into six big groups: biguanides (e.g. Metformin), sulfonylureas (e.g. Glimepiride), meglitinides (e.g. Repaglinide), thiazolidinediones (e.g. Pioglitazone), dipeptidyl peptidase IV inhibitors (DPP4, e.g. Linagliptin), and α-glucosidase inhibitors (e.g. Acarbose). Here, DPP4 is linked to diabetes mellitus.