OBJECTIVES: In January 2009, an authorization form was implemented which required Dutch clinicians to justify the prescription of branded statins, leading to significant switching of patients from atorvastatin to generic simvastatin. However, current prescription data indicates that much of this switching is occurring at less than equipotent doses. We sought to assess the potential consequences in terms of cardiovascular disease. METHODS: Data from a pharmacy database covering the majority of drug dispenses in the Netherlands informed dose-specific patterns of switching from atorvastatin to generic simvastatin. Dose-specific, LDL-C-modifying potencies of the two statins were derived from a recently-published meta-analysis. The relationship between reduction in LDL-C achieved by statin therapy and relative reduction in risk of coronary and stroke risk was derived from a recently-published meta-regression. This showed that for every 0.65mmol/L (25mg/dL) reduction in LDL-C, the relative risk (RR) (95% confidence interval [CI]) for a coronary and stroke event were 0.84 (95%CI 0.82-0.86) and 0.90 (95%CI 0.86-0.94), respectively. RESULTS: Out of the 39,031 Dutch patients who were switched from atorvastatin to generic simvastatin in the first quarter of 2009, 33.7%, 47.2% and 19.1% were switched to less potent, equipotent and more potent doses of simvastatin, respectively. The net (weighted-average) effect would have been a 5.6% increase in LDL-C. Assuming a baseline LDL-C of 2.5 mmol/L (98 mg/dL), the predicted relative increases (95%CI) in the risks of coronary and stroke events were 3.4% (3.0-3.9%) and 2.1% (1.3-3.0%), respectively. The equivalent figures for a baseline LDL-C of 3.0 mmol/L (117 mg/dL) were 4.1% (3.6-4.6%) and 2.6% (1.5-3.6%), and for a baseline LDL-C of 3.5 mmol/L (137 mg/dL), they were 4.8% (4.2-5.4%) and 3.0% (1.8-4.2%). CONCLUSIONS: In The Netherlands, many patients are being switched from atorvastatin to generic simvastatin at inferior doses, which might lead to a significant increase in future cardiovascular events.