Longitudinal examination of alcohol treatment episodes in the context of a changing minimum legal drinking age

Background: Establishing a safe drinking age is important because adolescent exposure to alcohol can impair neurological functioning and may be associated with greater vulnerability to alcohol use disorders; the latter assumption is based on small observational studies. Using large administrative databases, we examined whether exposure to a minimum legal drinking age (MLDA) under 21 was associated with later alcohol problems using alcohol treatment episodes as a proxy. Methods: From the Department of Health's Treatment Episode Data Set, we extracted alcohol-related treatment episodes from years 1992-2004 by state residence in five age cohorts. We used poisson regression to calculate incidence rate ratios for treatment based on age group exposure to the under-21 MLDA. Using states with historical 21-year MLDAs as the reference group, we calculated odds ratios of treatment for residents of states with an under-21 MLDA by year and age group. Results: Across 1992-2004, incident rate ratios of treatment were increased with exposure to under-21 MLDAs for 25-29 year-olds (IRR=2.1, p<.001) and 30-34 year-olds (IRR=1.6, p<.002) but not significantly so for older age groups. Odds ratios for treatment of residents in under-21 MLDA states were significantly higher for all ages through the mid 1990s, after which time rates converged with those with historically 21 year MLDA states. Discussion: Compared to residents of states whose MDLA was historically 21, residents of states with under-21 MLDAs were more likely to receive alcohol treatment, particularly those aged 25-34. With decreasing exposure to legal drinking under age 21, treatment rates across states have equalized.