Associations between county-level e-cigarette-inclusive Tobacco 21 law population coverage and e-cigarette use behaviors among United States adolescents in Monitoring the Future.

BACKGROUND AND AIMS: In the United States (US), Tobacco 21 (T21) laws set the minimum legal sale age for all tobacco products to 21 years. This study aimed to examine whether e-cigarette-inclusive T21 laws were associated with e-cigarette use behaviors and related disparities among US adolescents. DESIGN: We used nationally representative, repeated cross-sectional Monitoring the Future data to compare self-reported current e-cigarette use (2014-2022) and first e-cigarette initiation (2015-2022) among adolescents in counties with 100% ('full') versus <100% ('partial or no') e-cigarette-inclusive T21 law population coverage using modified Poisson regression, examining differences by sex, race and ethnicity, parental educational attainment and college educational expectations through interactions. SETTING: United States. PARTICIPANTS: 8th, 10th and 12th graders. MEASUREMENTS: County-level e-cigarette-inclusive T21 law population coverage was determined using Tobacco 21 Population Coverage Database and US Census Bureau population data. Current e-cigarette use was defined as any past 30-day use among the entire sample. First e-cigarette initiation was defined as first use in the current grade among adolescents who had not initiated use prior to the current grade. FINDINGS: Compared with 8th, 10th and 12th graders in counties with partial or no e-cigarette-inclusive T21 law coverage, 8th [marginal effect (ME) = -1.8%, 95% confidence interval (CI) = -3.1% to -0.6%], 10th (ME = -2.6%, 95% CI = -4.6% to -0.6%) and 12th graders (ME = -2.7%, 95% CI = -5.2% to -0.1%) in counties with full coverage had a lower current e-cigarette use prevalence. For current e-cigarette use, we also observed statistically significant interactions by sociodemographic factors. Across all grades, full [8th: predicted prevalence (PP) = 5.9%, 95% CI = 4.7%-7.1%; 10th: PP = 11.8%, 95% CI = 10.2%-13.4%; 12th: 18.1%, 95% CI = 15.6%-20.6%] versus partial or no coverage (8th: PP = 7.5%, 95% CI = 6.2%-8.8%; 10th: PP = 16.3%, 95% CI = 15.0%-17.6%; 12th: 23.4%, 95% CI = 21.9%-24.8%) was associated with lower current e-cigarette use among males but not females. By race and ethnicity, associations were statistically significant across all grades, but the magnitude and direction of these associations varied by subgroup and grade. Among 12th graders, full (PP = 16.1%, 95% CI = 13.9%-18.3%) versus partial or no coverage (PP = 20.5%, 95% CI = 19.0%-22.1%) was associated with lower current e-cigarette use among those who said they 'probably will' graduate from a four-year college but not among those with other educational expectations. We did not find sufficient evidence to support an association between e-cigarette-inclusive T21 law coverage and first e-cigarette initiation overall or across sociodemographic subgroups. CONCLUSIONS: E-cigarette-inclusive Tobacco 21 laws appear to be associated with lower current e-cigarette use among US adolescents. However, we lacked sufficient evidence to support an association with first e-cigarette use initiation. We also observed sociodemographic differences in these associations for current e-cigarette use.