This prospective observational study will evaluate whether the SLC16A11 risk variant influences the response to metformin in adults with type 2 diabetes. Participants will be classified as carriers or noncarriers and followed for 6 months while receiving extended-release metformin titrated to the maximum tolerated dose, between 1,500 and 2,250 mg/day. The primary outcome is the change in glycated hemoglobin, with additional assessment of seven-point capillary glucose profiles, liver enzymes, visceral fat, lipid profile, and lactate concentrations. The study plans to include 154 participants to compare treatment response between both genetic groups and explore the potential value of a more personalized therapeutic approach.