Objectives: One recent analysis of brand to generic switching patterns in a large, nationally representative pharmacy claims database from January 2005 to June 2006 suggested that 3% of patients taking atorvastatin were switched to simvastatin. However, 38% of these switches were to less potent doses. This analysis sought to assess the long-term impact of this switching pattern in the US. Methods: A Markov model simulated the future cardiovascular health of Americans aged 35-74 years who were initially free of cardiovascular disease (CVD), but who met NCEP-ATPIII criteria for lipid-lowering treatment. Follow-up occurred until age 75 years. Decision analysis was used to compare the effects of prescribing all subjects atorvastatin versus prescribing 97% atorvastatin and 3% simvastatin. Subjects were profiled on participants of the 1999-2004 NHANES. The risks of CVD and death were estimated from application of a Framingham risk equation and derived from US mortality statistics, respectively. The costs of CVD and statins were derived from administrative health-care claims data. A uniform 3% annual discount rate was applied. Results: The analysis estimated a cohort of 24,037,997 Americans. If all were to be prescribed atorvastatin, 24.0% would be expected to suffer a cardiovascular event and 24.2% to die by age 75. If 3% were to be prescribed simvastatin at the observed pattern, the equivalent figures would be 24.1% and 24.3%, representing an excess of 2317 cardiovascular events and 9987 deaths, respectively. There would be a net cost saving associated with the switch, but at $42,400 per year of life lost and $27,700 per QALY lost. Conclusions: In the US, many patients are being inappropriately switched from atorvastatin to generic simvastatin, which might lead to an increase in cardiovascular events and overall mortality for little health-economic gain.