Age-related Changes in Past-Month Alcohol, Cannabis, and Simultaneous Use in a Statewide Sample of Young Adults in Washington State.

Abstract

It is unknown whether age-related decreases in substance use (maturing out) are observed in the legalized cannabis context. This study evaluated age-related changes in past-month alcohol use frequency, cannabis use frequency, and any simultaneous alcohol and marijuana/cannabis (SAM) use among young adults who engaged in the respective substance use behavior. Young adults, residing in Washington State at enrollment (N=6,509; 68.3% female; ages 18-25), provided 3-5 years of annual data in a longitudinal, cohort-sequential design from 2015 to 2019, a period after nonmedical cannabis was legalized and implemented. Multilevel growth models were conducted; post-stratification weights were applied to make the sample more similar to the Washington young adult general population in demographic characteristics. Among those who reported alcohol use at 1+ timepoints, days of alcohol use increased from age 18 to approximately age 25 and then decreased until age 30. Among those who reported cannabis use at 1+ timepoints, days of cannabis use increased from age 18 until approximately age 23 and then decreased until age 30. Among those who reported SAM use at 1+ timepoints, the probability of SAM use increased from age 18 until approximately age 24 and then decreased until age 30. Age-related changes in SAM use were largely explained by concurrent changes in alcohol and cannabis use frequency. Maturing out was observed for alcohol, cannabis, and SAM use among those who used each respective substance, with evidence that age-related changes in SAM use were tied to alcohol and cannabis use frequency.