GLP1R and type 2 diabetes mellitus: Metformin, a biguanide, used to be the only initial pharmacological therapy recommended by the American Diabetes Association (ADA) for T2DM until the advent of GLP-1 RA, approved by the FDA for treatment of T2DM in 2005 [3] and SGLT-2i, approved by the FDA for treatment of T2DM in 2013 [4].