Does health insurance increase health care utilization? evidence of ex-post moral hazard from the Social Security Scheme in Thailand

Expanding health insurance improves access to care, but it may also increase healthcare utilization and fiscal pressure on public systems. Using multiple waves of the Thailand Socio-Economic Survey, this study applies a difference-in-differences (DD) approach combined with propensity score matching to estimate the causal effect of Social Security Scheme (SSS) coverage. The results show that insurance coverage increases healthcare utilization, consistent with behavioral responses associated with ex-post moral hazard, although part of this increase reflects improved access to necessary care. The magnitude of the effects varies across types of medical expenditures, estimation methods, and study periods. These findings highlight the importance of balancing expanded healthcare access with the financial sustainability of the SSS. Policymakers may consider targeted cost-management measures, efficiency improvements, and strengthened preventive health policies while maintaining equitable access to healthcare services.