GCG and type 2 diabetes mellitus: Though heterogeneities in treatment protocol and drug dosage existed, results showed that add-on therapy of GLP-1 analogues (liraglutide, exenatide, and lixisenatide) and DPP-4 inhibitors (linagliptin, sitagliptin, and aloglitpin) were effective in improving glycaemic control among type 2 diabetic patients.