Trends in Simultaneous Alcohol and Marijuana Use Among US Young Adults, 1977-2014

Introduction: Young adulthood (ages 19-30) is a period of elevated vulnerability for participation in high-risk behaviors, including simultaneous alcohol and marijuana (SAM) use. SAM use results in additive effects on a range of cognitive, perceptual and motor functions, with clearly increased risk for behaviors such as driving. SAM use has been significantly and positively associated with social consequences, alcohol dependence, depression, and other health problems. This paper examines historical trends in SAM use prevalence across young adulthood among national samples of US young adults.

Methods: Data on past 12-month alcohol, marijuana, and SAM use at one or more of three modal ages (19/20, 23/24, 27/28) were collected from 11,758 individuals from 1977-2014. Participants were in the longitudinal Monitoring the Future panel study, beginning as high school seniors in the classes of 1976-2013. Historical trends by modal age in any 12-month SAM use, frequent SAM use (simultaneous alcohol use most or every time marijuana was used), and alcohol and marijuana use were estimated using the Joinpoint Regression Program.

Results: Recent (combined 2012-2014) SAM use prevalence estimates among all respondents were 25%, 24%, and 18% for ages 19/20, 23/24, and 27/28, respectively. Comparative estimates for frequent SAM use were 4%, 6%, and 5%. Since 1977, an average of 80% of all young adults (regardless of modal age) who reported past 12-month marijuana use also reported any SAM use. For each modal age examined, significant decreases in any SAM use prevalence were observed through the early 1990s. From the early 1990s onwards, modeled trends indicate any SAM use prevalence remained stable among those at the end of young adulthood, but increased significantly among early- and mid-young adults (with the strongest rate of increase observed at modal age 23/24). Observed trends closely followed those for any past 12-month marijuana use. In contrast, trends in frequent SAM use generally paralleled those for past 12-month alcohol use. A significant and linear decrease over time in the prevalence of reporting frequent SAM use was observed for early young adults. For mid- and late-young adults, significant decreases were observed until the early 1990s, after which rates remained statically stable.

Conclusions: Any SAM use has been increasing among US early- and mid-young adults, and can be expected to closely follow overall marijuana use prevalence levels. These findings suggest the importance of screening and prevention messaging targeting young adults (both users and their peers) to increase awareness of the pharmacological risks associated with combining alcohol and marijuana use over and above those associated with use of either substance separately.