OBJECTIVES: To evaluate cost-effectiveness of adding ezetimibe to simvastatin versus a switch to rosuvastatin or atorvastatin for high CHD risk patients who cannot attain treatment goal (LDL-C ≥ 100 mg/dL) on their current simvastatin dosage from Thai payer perspective.  METHODS: A published Markov model (Cook et al. 2004) was used to project lifetime costs and outcomes of lipid-lowering treatment in primary and secondary CHD prevention. Lipid efficacy data were obtained from clinical trials. Risks of CHD events and non CHD-related mortality rates were estimated by using Framingham Heart Study risk equations and information from Ministry of Public Health (MOPH), respectively. Disease-related costs were obtained from published local studies. Drug prices were those published by MOPH. All costs were expressed in THB 2010 values. Future costs and outcomes were discounted at 3%. Two scenarios were compared in the analysis: the addition of ezetimibe to simvastatin 20 mg versus switching to rosuvastatin 10 mg and the addition of ezetimibe to simvastatin 40 mg versus switching to atorvastatin 40 mg. RESULTS: Ezetimibe co-administration increased life expectancy (LY) by 0.15 and 0.26 years and resulted in 0.07 and 0.12 additional quality-adjusted life years (QALY) when compared to a switch to rosuvastatin and a switch to atorvastatin, respectively. The QALY gained would yield lifetime cost-savings of Baht 1,106 and 2,137 per patient for such comparisons. Similar results were obtained where costs and outcomes were either discounted or undiscounted. The sensitivity analyses showed that results were robust to changes across scenarios.      CONCLUSIONS: This analysis suggested that addition of ezetimibe to simvastatin is the dominant treatment strategy (more effective and less costly) in both scenarios. The results are very imperative to assist policy decision-making in order to increase access to second-line treatment option for patients not achieving lipid treatment goals with simvastatin monotherapy in Thailand.