It would be difficult to conduct a randomized trial of alcohol initiation in human adolescents, but a natural experiment of this kind was created by changing minimum legal drinking age (MLDA) laws in the United States during the 1970’s and 1980’s. From the repeal of alcohol prohibition in 1933 until the early 1970’s, most US states maintained a minimum legal alcohol drinking age of 21 years. Then, in the early 1970’s, as the federal voting age was being lowered to 18, 26 states lowered the age of majority for possession or purchase of alcohol as well (Wechsler & Sands, 1980). By the mid-1970’s, research studies began to report a link between lower drinking ages and rising rates of motor vehicle crashes among young drivers; 16 states increased their MLDA’s between 1976 and 1983 and in 1984, Congress passed the National Minimum Drinking Age Act (23 USC §158) directing the Secretary of Transportation to withhold a percentage of otherwise allocable federal highway funds from States “in which the purchase or public possession … of any alcoholic beverage by a person who
