The risks of alcohol consumption differ by the presence or absence of simultaneous use of other substances, the most common one being marijuana. Simultaneous alcohol and marijuana use may increase alcohol-related risks and societal costs. This paper examined historical changes in simultaneous alcohol/marijuana use among young adult alcohol users from 1977–2016.

The authors used data on previous 12-month alcohol, marijuana, and simultaneous alcohol/marijuana use at six age points—19/20, 21/22, 23/24, 25/26, 27/28, and 29/30 years of age—among 11,789 individuals (6,484 women, 5,305 men) who reported using alcohol in the past 12 months and were participating in the Monitoring the Future study. The yearly prevalence of simultaneous alcohol/marijuana use among those who reported drinking alcohol in the past 12 months was calculated for each age group and associated trends across time were examined.

The number of early- and mid-young adult alcohol users who reported simultaneous alcohol and marijuana use increased significantly. The highest risk was found among alcohol users in their early 20s. The authors speculated that simultaneous alcohol and marijuana use by young adult drinkers increases as young adult marijuana use increases, and thus the number of young adult drinkers who report simultaneous alcohol and marijuana use may continue to increase with growing marijuana use. Based on these findings, they called for more research on how use of a secondary substance such as marijuana may influence how alcohol is used.

—Newswise