In South Korea, the market for over-the-counter drug advertising (OTCA) has been increasing in recent years; however, research on OTCA has received scant attention from a psychological perspective. Identifying the antecedents and underlying mechanisms of behavioral responses to OTCA helps us understand how consumers engage in health-related decisions. This study focused on a notable theoretical framework that determines behavioral responses to OTCA. Specifically, this study examined the sequential relationship between health consciousness, attention to OTCA, attitude toward OTCA, and behavioral responses to OTCA. It also tested the boundary conditions of the effect of attitude toward OTCA on behavioral responses by examining the moderating role of subjective health knowledge. A nationwide online survey was conducted. The results showed signifificant dual mediating effffects of attitude and attention on behavioral responses. However, subjective health knowledge did not signifificantly moderate the sequential relationship between attitude toward OTCA and behavioral responses. These fifindings have implications for strategy, policy, and practice in both public health fifields and the advertising industry. Advertising practitioners and healthcare professionals can gain valuable insights into how to enhance consumers’ health-related decision-making for sustainable health promotion.