Beyond Tobacco Prevention: The Effects of Tobacco 21 Laws on Young Adults' Body Weight

Tobacco 21 (T21) laws effectively reduce youth tobacco use by preventing initiation. This study examines their impact on body weight among young adults aged 18-20. Using 2009-2019 Behavioral Risk Factor Surveillance System data and a two-way fixed-effects difference-in-differences (DID) design, we find limited evidence of broad weight changes in either direction across the BMI distribution. Obesity declines due to modest weight reductions concentrated near the upper BMI threshold, with no significant changes in overweight status or average BMI. Event study shows that the obesity decline emerges in the first post-T21 year and attenuates afterward. Results are robust to alternative specifications, including an imputation DID approach addressing staggered adoption. Effects are driven by "never smokers", consistent with a prevention-based pathway, and are more pronounced among males and non-White individuals, with heterogeneity observed across education levels in the upper BMI tail. Supplemental analyses using Youth Risk Behavior Survey data show reduced adverse weight outcomes among high schoolers aged 18+. T21 laws increase exercise, improve diets, and reduce sedentary behavior, underage drinking, marijuana use, and mental distress. Overall, T21 laws avoid the typical cessation-related weight gain and modestly improve weight outcomes among at-risk young adults, suggesting broader public health benefits beyond tobacco prevention.