Marijuana use increased and the drug's perceived harmfulness decreased among eighth- and 10th-graders in Washington after marijuana was legalized for recreational use by adults but there was no change among 12th-graders or among students in the three grades in Colorado after legalization for adults there, according to a new study published online by JAMA Pediatrics.
Washington and Colorado became the first two states to legalize recreational use of marijuana for adults in 2012, followed by handful of other states since. The potential effect of legalizing marijuana for recreational use has been a topic of considerable debate.
Magdalena Cerdá, Dr.P.H., M.P.H., of the University of California Davis School of Medicine, Sacramento, and coauthors examined the association between legalizing recreational use of marijuana for adults in the two states and changes in perception of harmfulness and self-reported adolescent marijuana use before and after legalization.
The authors used data from nearly 254,000 students in the eighth, 10th and 12th grades who took part in a national survey of students. They compared changes prior to recreational marijuana legalization (2010-2012) with post-legalization (2013-2015) and with trends in other states that did not legalize recreational marijuana.
In Washington among eighth- and 10th-graders, perceived harmfulness declined 14.2 percent and 16.1 percent, respectively, while marijuana use increased 2.0 percent and 4.1 percent, respectively. Among states that did not legalize recreational marijuana use, perceived harmfulness decreased 4.9 percent and 7.2 percent among eighth- and 10th-graders, respectively, and marijuana use decreased by 1.3 percent and 0.9 percent, respectively, according to the results.
No changes were seen in perceived harmfulness or marijuana use among Washington 12th-grades or students in the three grades in Colorado, for which researchers offer several explanations in their article.
The authors also offer several potential explanations for the increase in marijuana use among eighth- and 10th-graders in Washington, including that legalization may have increased availability through third-party purchases. Limitations of this study include that it relied on self-reported marijuana use. Also, analysis specific to the states of Washington and Colorado may not be generalizable to the rest of the United States.
"Although further data will be needed to definitively address the question of whether legalizing marijuana use for recreational purposes among adults influences adolescent use, and although these influences may differ across different legalization models, a cautious interpretation of the findings suggests investment in evidence-based adolescent substance use prevention programs in any additional states that may legalize recreational marijuana use," the article concludes.