Type 2 diabetes (T2D) is a global epidemic, and nations are struggling to implement effective healthcare strategies to reduce the burden. While efficacy studies demonstrate that metformin can reduce incident T2D by half among younger, obese adults with prediabetes, its real-world effectiveness are understudied, and its use for T2D prevention in primary care is low. We describe the design of a pragmatic trial to evaluate the incremental effectiveness of metformin, as an adjunct to a simple lifestyle counseling.