This is the first study to document a long-term association between policies governing access to alcohol in young adulthood and risk of alcohol or substance use disorders in later adulthood. We find a clinically large and statistically robust association. For example, adults who would have been legally allowed to purchase alcohol before age 21 were about 33% more likely to have a past-year alcohol or drug use disorder than adults who could not legally purchase alcohol until age 21 (odds ratio 1.33, p < .0001), and the association persists even among respondents in their 40’s and 50’s. These surprisingly strong results are consistent with the hypothesis that late adolescence may be a ‘sensitive period’ for an environmental exposure closely tied to the timing of changing minimum legal purchase age laws. However, the MLDA effects do not seem to be working through age of drinking initiation, per se; instead, we hypothesize that the long term effects of MLDA exposure may work through the frequency and intensity of drinking or the social networks and social norms around drinking that develop in late
