GLP1R and diabetes mellitus: GLP-1 receptor agonists and DPP-4 inhibitors are included in the 2012 American Diabetes Association (ADA)/European Association for the Study of Diabetes (EASD) and 2013 American Association of Clinical Endocrinologists (AACE) guidelines as second-line therapy for patients who do not achieve glycemic control with metformin therapy and lifestyle modifications alone.