In addition to the many drugs currently used to treat diabetes (e.g., nateglinide, metformin, dipeptidyl peptidase-4 (DPP-4) inhibitors, linagliptin, and α-glycosidase inhibitors) [82,83,84,85,86], there are ongoing efforts to develop new natural drugs to the treatment of diabetes without side effects (Table 2). Here, DPP4 is linked to diabetes mellitus.