Association of Metformin Use With Risk of Venous Thromboembolism in Adults With Type 2 Diabetes: A General-Population–Based Cohort Study

Metformin is hypothesized to protect against the risk of venous thromboembolism (VTE); however, there is a paucity of data supporting this hypothesis. Among individuals aged 40-90 years with a diagnosis of type 2 diabetes in the Health Improvement Network database (2000-2019), we compared the risks of incident VTE, pulmonary embolism, and deep vein thrombosis among metformin initiators with those among sulfonylurea initiators. Individuals were followed from their first prescription refill to an incident VTE, drug discontinuation, switching or augmenting, plan disenrollment, or the end of the study, whichever occurred first. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using the Cox model, adjusting for confounders using inverse probability of treatment weighting. Among 117,472 initiators of metformin and 13,835 initiators of sulfonylureas, 555 (1.3/1,000 person-years) and 75 (2.1/1,000 person-years) VTE cases occurred in each group, respectively. The multivariable-adjusted HR was 0.65 (95% CI: 0.51, 0.84). The corresponding risks for pulmonary embolism (adjusted HR = 0.71, 95% CI: 0.50, 1.01) and deep vein thrombosis (adjusted HR = 0.64, 95% CI: 0.48, 0.87) were also lower in metformin initiators than in sulfonylurea initiators. Our study provided empirical evidence to support a lower risk of VTE after initiation of metformin as compared with sulfonylureas among patients with type 2 diabetes.