Aim: Although, the effectiveness of metformin in diabetes treatment is well established, its preventive effect in the development of diabetes is still unclear in real world. We aimed to determine the effectiveness of metformin therapy as a single preventive agent in patients with prediabetes in a cohort study (IDPS).

Study Design: In this prospective observational study.

Place and Duration of Study: Isfahan Endocrine and Metabolism Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.

Methodology: We included 410 patients with prediabetes (168 metformin user, 242 non-users), who participated in IDPS. To determine the association between metformin use and incidence of type 2 diabetes, Cox proportional hazard method, Kaplan-Meier and log Rank test were used.

Results: In fully adjusted model for all confounders, significant hazard ratio (HR) for staying prediabetes rather than returning to normal was detected in male group of metformin non-user (HR: 2·41 [95% CI 1.01-5.79]; P<0·05) and those metformin non-user who had both Impaired Fasting Glucose and Impaired Glucose Tolerance (IFG & IGT) (HR: 2.13 [95% CI 1.05-4.34]; P=0·04).  There was no significant difference in terms of developing diabetes risk between metformin users and non-users.

Conclusion: This study evidenced that males and patients with IFG & IGT who had not used metformin are at higher risk to staying prediabetes than returning to normal.