Differential impact of South Korea’s 2019 E-cigarette advisory on adult tobacco product use: an interrupted time series analysis by product type and subgroup

In October 2019, South Korea’s Ministry of Health and Welfare issued a national advisory urging the public to refrain from using liquid-type/ electronic cigarettes (e-cigarettes) due to international concerns over vaping-related lung injuries. This study evaluates changes in e-cigarette use trends using nationally representative repeated cross-sectional survey data. We conducted an interrupted time-series (ITS) analysis using age-standardized prevalence data on current use of cigarettes, e-cigarettes (2013–2023), and heated tobacco products (HTPs, 2019–2023) from the Korea National Health and Nutrition Examination Survey. ITS regression models with Newey–West standard errors assessed pre-intervention trends, immediate level changes, and post-intervention trend differences. Subgroup analyses were performed by gender, age, region, and income. We also conducted sensitivity analyses using ± 1-year intervention timings and presented counterfactual projections. E-cigarette use had been increasing before 2019 (+ 0.43% points/year, 95% CI: 0.11, 0.75), and a decline was observed in 2019 relative to prior trends (–1.33 pp, 95% CI: − 2.54, − 0.12), with no significant change in trend post-intervention. Subgroup effects varied, with men (–2.35 pp, 95% CI: − 4.39, − 0.30), middle-aged adults (e.g. 40–49 years: − 2.94 pp, 95% CI: − 5.36, − 0.52), and low-income individuals (–2.65 pp, 95% CI: − 3.07, − 2.24) showing the largest reductions. No compensatory increases were observed in cigarette or HTP use. Sensitivity tests confirmed the robustness of results to alternate intervention dates. The 2019 EVALI outbreak and the South Korean government’s advisory were associated with a decline in e-cigarette use at the population level, particularly among high-use subgroups. These findings suggest a potential role for timely public health advisories and risk communication in shaping behavior, even in the absence of binding regulations. The intervention illustrates how timely risk communication may contribute to measurable changes in health behavior at the population level.