Introduction: Pharmacogenetics can be used in clinical analysis to assess the efficiency of drugs according to the patient’s genetic profile, and it is becoming important for population genetics and precision medicine. The type 2 diabetes mellitus (T2DM) is highly prevalent all over the world, including Peru. Among the different drugs for T2DM, metformin is used the most and patient’s response to it can be influenced by the Val/Met polymorphism of the OCT1 (SLC22) gene, where Met is associated with a lower response. The frequencies of these polymorphisms vary according to ethnic origin. Objective: To evaluate the distribution of the Val/Met polymorphism in the OCT1 gene in samples of Lima and Puno, and to assess their impact on pharmacogenetics of T2DM. Design: Descriptive, cross-sectional study. Settings: Faculties of Pharmacy and Biochemistry, and Medicine, Universidad Nacional May...