This study reports on allelic and genotypic frequencies of OCT1, OCT2, OCT3 polymorphisms among metformin-treated DMT2 patients. It also reports the association with HbA1c control on 59 DMT2 patients. They were genotyped through real-time PCR (TaqMan assays). Metformin plasmatic levels were determined through mass spectrometry. Neither the analysis of HbA1c control by SNPs in SLC22A1, SLC22A2, and SLC22A3, nor the dominant genotypic model analysis yielded statistical significance across genotypes in polymorphisms rs72552763 (p=0.4678), rs622342 (p= 0.2215), rs316019 (p=0.2209), and rs2076828 (p=0.215). HbA1c levels were different in rs72552763 (p= 0.0220) and rs622342 (p=0.0093) genotypes. The dominant genotypic model found the lowest HbA1c levels by GAT/GAT (p= 0.0058) and A/A (p=0.0108), in rs72552763 and rs622342 respectively. We may conclude that rs72552763 and rs622342 polymorphisms in SLC22A1, exercise a relevant effect in metformin response determined by HbA1c levels among Mexican-Mestizo DMT2 patients.