Dipeptidyl peptidase-4 (DPP-4) could inhibit the GLP-1 and GIP activity, so the inhibitors of DPP-4 along with several types of GLP-1 and GIP analogues have been applied in clinical therapy of T2DM; however, more research is needed to clarify the therapeutic use of these medications for T2DM (79) (Figure 1). Here, GCG is linked to type 2 diabetes mellitus.