Background In the USA, many states do not pre-empt municipalities from enacting stricter tobacco-control policies than state or federal laws. Several municipalities in Massachusetts have passed progressive local laws aimed at reducing adolescent tobacco use. We exploited this variability to examine the associations between county-level flavoured tobacco product restrictions, tobacco 21 policies and smoke-free laws prohibiting e-cigarettes with adolescent cigarette and e-cigarette use in Massachusetts, and to assess whether policy effects varied by age.

Methods We conducted difference-in-differences models to link changes in county-level tobacco-control policies to changes in adolescents’ use of cigarettes and e-cigarettes using 2011–2017 biennial Massachusetts Youth Health Surveys.

Results Counties with greater implementation of flavoured tobacco product restrictions were associated with a decrease in the level of cigarette use among users (Coefficient −1.56; 95% CI −2.54 to −0.58). A significant interaction (p=0.03) revealed the largest reductions among 14 and 18 year olds. Increasing flavoured tobacco product restrictions were also associated with reductions in the likelihood of e-cigarette use (Coefficient −0.87; 95% CI −1.68 to −0.06). Increasing tobacco 21 restrictions were associated with decreases in cigarette use only among 18 year olds, while there was no evidence of associations between smoke-free laws with use of either tobacco product.

Conclusions Adolescents in Massachusetts decreased their use of cigarettes and e-cigarettes in response to local restrictions that limited the sale of flavoured tobacco products to adult-only retail tobacco stores. Local legislation can reduce adolescent tobacco use and municipalities should enact stricter tobacco-control policies when not pre-empted by state law.