Grade Level Differences in Trends in Adolescent Marijuana Use in Washington State, 2004-2016

Introduction. Along with Colorado, Washington was the first state to pass a recreational marijuana law in 2012. Given concerns about the impact of retail marijuana on adolescent use, ongoing monitoring of changes in adolescent marijuana use in Washington is needed. In this presentation, we will examine trends in marijuana use among 8^th, 10^th, and 12^th graders in Washington state, with a focus on investigating differences by grade level and race/ethnicity.

Methods. We used data from the biennial Healthy Youth Surveys from 2004-2016, a statewide, representative sample of 8^th, 10th, and 12^th grade students (n=161,992). We used multiple logistic regression to conduct trend analyses, and assessed linear and quadratic trends in marijuana use from 2004-2016 for the full sample and stratified on grade level and race/ethnicity, and adjusted for school clustering and sex. Outcomes include any past 30-day marijuana use and frequent use (ie, >6 times in the past 30 days).

Results. There was a modest linear increase in past 30-day marijuana use over the study period (14.7%-16.4%) for the full sample. In analyses stratified by grade, we observed: [1] no change in past 30-day use among 10th graders (17.0%-17.2%, aOR=1.00, 95% CI: 0.98-1.00), [2] a statistically significant linear decrease among 8th graders (9.2%-6.4%, aOR=0.96, 95% CI: 0.94-0.99), and a statistically significant linear increase among 12th graders (19.4%-26.5%, aOR=1.05, 95% CI:1.04-1.07). The increase was particularly high for Hispanic/Latino 12th graders (12.9%-25.2%, 1.12, 95% CI: 1.03-1.07).

Conclusions. Although we observed a modest increase in marijuana use among 8th, 10th, and 12th graders combined in Washington State from 2004-2016, further analyses show that there are differences by grade level; increases in use were found among 12^th grade students. Increases in use were largest among Hispanic/Latinos students, and future research should test explanations for this increase, one such explanation is that there were more foreign-born Hispanics in earlier survey years, and being born outside the US is a protective factor in marijuana use. Findings highlight the need for further study into developmental/cultural explanations for age differences to inform prevention and intervention efforts.