Underage drinking and illicit drug use, especially marijuana use, are closely linked according to data from the 2011 National Survey on Drug Use and Health. Twenty percent of underage drinkers reported using at least one illicit drug within two hours of last using alcohol, compared to 4.9% of those aged 21 or older. Marijuana was by far the most commonly used substance at 19.2% for drinkers under 21 and 4.4% for older drinkers.
The authors of the analysis suggest the need to follow any changes in Washington and Colorado where recreational marijuana is legalized. Since there seem to differences in how teens use marijuana and how adults use marijuana, it will be important to study the impact of legalization on teens separately from the impact on adults.