Age-Related Changes in Past-Month Alcohol, Cannabis, and Simultaneous Use in a Statewide Sample of Young Adults in Washington State
Alcohol and cannabis use during young adulthood remain significant public health concerns due to their high prevalence and associated adverse consequences, with approximately 20-25% of young adults engaging in simultaneous alcohol and cannabis use (SAC), defined as using both substances such that their effects overlap. Previous research has demonstrated that SAC use is associated with increased alcohol consumption, prolonged cannabis intoxication periods, and greater alcohol-related consequences, and while maturing out effects in substance use have been observed with increasing age, limited knowledge exists regarding age-related changes in SAC use within legalized cannabis contexts and whether such changes can be attributed to concurrent variations in alcohol and cannabis use frequency. Therefore, the present study aimed to examine age-related changes in past-month alcohol and cannabis use frequency and the probability of past-month SAC use among young adults in Washington State, where nonmedical cannabis use has been legalized since 2012, utilizing a longitudinal data from 2015 to 2019.
The study utilized an accelerated longitudinal cohort-sequential design from the Washington Young Adult Health Survey, targeting 6,509 young adults aged 18-25 residing in Washington State. Data collection was conducted through baseline and annual follow-up surveys, with past-30-day alcohol and cannabis use frequency measured by having participants enter the number of use days as integers, while SAC use was assessed by measuring the frequency of simultaneous alcohol and cannabis use with overlapping effects using categorical responses, which were subsequently recoded into dichotomous variables. The collected data were analyzed using negative binomial growth models for age-related changes in alcohol and cannabis use frequency, and logistic growth models for age-related changes in the probability of SAC use, with all models employing multilevel growth modeling that centered age at 21 years and year at 2017, while controlling for biological sex, race/ethnicity, and geographic region.
The results revealed that alcohol use frequency exhibited a curvilinear pattern with a peak at approximately age 25, increasing from 1.48 days at age 18 to 5.20 days at age 25, then decreasing to 2.75 days at age 30. Cannabis use frequency also showed a curvilinear pattern with a peak at approximately age 23, increasing from 3.70 days at age 18 to 5.29 days at age 23, then decreasing to 3.18 days at age 30. Regarding SAC use probability, the initial model without controlling for alcohol and cannabis use frequency demonstrated a curvilinear pattern with a peak at approximately age 24, increasing from 0.48 at age 18 to 0.60 at age 24, then decreasing to 0.46 at age 30, suggesting a maturing out effect during young adulthood. However, when alcohol and cannabis use frequency were controlled, the statistically significant association between age and SAC use probability disappeared, showing a non-significant linear decrease from age 18 to 30, indicating that age-related changes in SAC use can be largely attributed to concurrent changes in alcohol and cannabis use frequency. These findings demonstrate that the traditional maturing out pattern is maintained even in the context of cannabis legalization, with important implications for prevention strategy development, as the reduction in SAC use is partially explained by decreases in individual substance use frequency.
Takeaway: Age-related changes in simultaneous alcohol and cannabis use among young adults are largely driven by concurrent changes in individual substance use frequency rather than representing an independent developmental pattern.