All are proved to delay or prevent diabetes in those with impaired glucose tolerance, except

Intensive changes in lifestyle (diet and exercise for 30 min/d five times/week) in individuals with IGT prevented or delayed the development of type 2 DM by 58% compared to placebo. In the same study, metformin prevented or delayed diabetes by 31% compared to placebo.A number of agents, including a-glucosidase inhibitors, metformin, thiazolidinediones, GLP-1 receptor pathway modifiers, and orlistat, prevent or delay type 2 DM but are not approved for this purpose. Pharmacologic therapy for individuals with prediabetes is currently controversial because its cost-effectiveness and safety profile are not known. Ref: Harrison 19e pg: 2406