Marijuana use among teenagers in Washington declined after the state legalized recreational marijuana in 2012, contradicting earlier estimates about the trend, according to a new study by Multnomah County Epidemiologist Julia Dilley, Ph.D., in partnership with researchers from the Oregon Health Authority, Washington Liquor and Cannabis Board, and RAND Corporation.
Marijuana use dropped a small, but statistically significant amount among eighth graders and 10th graders in Washington between 2014 and 2016, the study found.
Markets opened in July 2014 to sell pot in Washington to people 21 and older. Parents, public health experts and local governments worried legalization would make it easier and more acceptable for teens to use the drug. A 2017 study of teen cannabis use following legalization found teens perceived marijuana as less harmful and reported that Washington youth in 8th and 10th grade used marijuana slightly more than in prior years, although the study did not find changes in use among 12th graders in Washington, or youth in any grades in Colorado, which also legalized recreational marijuana use in the same year.
That study relied on information from Monitoring the Future, a national survey of teen behavior and attitudes. The national survey was not designed to provide state-representative estimates, however. It included a relatively small sample for the state of Washington.
The new study relied on results from the Washington Healthy Youth Survey, taken from a random sample of public schools every two years. More schools and more students are captured in the state survey, and those students are more representative of the state’s youth population. For example, the Washington youth survey included more students from lower-income families and more students of color than the Monitoring the Future survey.
Rates of marijuana use might be influenced by local policies about retail licenses or by demographics. And the effects of legalization may be hard to tack down in an emerging market that will take time to mature.
As part of continuing to study the effect of legalization on youth, Dilley and her partners are working on additional papers that parse the state health survey data to compare the effects of legalization on urban and rural communities, people of different ages and genders, and communities of color.
“What our study shows is, it’s too early to draw conclusions about the effect of legalization. We just need to keep looking at this,” researcher Dilley said. “We need more information, over time, from different places, and within specific groups.”
