Tobacco 21 policies in California and Hawaii and sales of cigarette packs: a difference-in-differences analysis.

OBJECTIVE: To measure the association of raising the minimum legal age of tobacco sales to 21 years (T21) statewide with monthly sales of cigarette packs in California and Hawaii, the first two states to implement T21 statewide.
METHODS: State monthly cigarette tax revenues from state departments of taxation were analysed for 11 states from January 2014 through December 2018 (n=660). Monthly cigarette packs sold were constructed using cigarette tax revenue and cigarette tax rate in each state. A difference-in-differences regression method was used to estimate the association of statewide T21 policies with monthly cigarette packs sold in California and Hawaii, separately, compared to the western states that did not implement such policies. Both models were controlled for year-month fixed effects, cigarette tax rates, smoke-free air laws, Medicaid coverage of smoking cessation, minimum legal sales ages for e-cigarettes and state marijuana laws, in addition to state demographic characteristics (sex, age, education, race/ethnicity and population size).
FINDINGS: Implementation of T21 statewide was associated with a reduction of 9.41 (95% CI=-15.52 to -3.30) million monthly packs sold in California and 0.57 (95% CI=-0.83 to -0.30) million monthly packs sold in Hawaii, compared to regional states. These translate to a reduction of 13.1%-18.2%, respectively, in monthly packs sold relative to mean values before the implementation of T21.
CONCLUSIONS: Raising the minimum legal age for tobacco sales to 21 years could reduce cigarette sales as part of a comprehensive tobacco control strategy that complements and builds on proven approaches to achieve this goal. © Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.