SLC22A1 and type 2 diabetes mellitus: The aims of our study were to evaluate the efficacy of metformin and the digestive tolerance to metformin in 73 newly-diagnosed type 2 diabetic patients based on M420del (rs72552763), R61C (rs12208357) and G401S (rs34130495) polymorphism of SLC22A1 gene encoding for OCT1.