Marijuana use significantly increased and its perceived harm decreased among eighth- and 10th-graders in Washington state following enactment of recreational marijuana laws, according to a study published online in JAMA Pediatrics. There was no change in use or perceived harm among 12th graders or among similar grades in Colorado.
The authors believe the study, conducted by UC Davis and Columbia University Mailman School of Public Health, is the first in the nation to assess changes in teens’ perceptions and marijuana use before and after legalized recreational use, and compare these attitudes and use in 45 other contiguous states where marijuana use is not legal.
The data showed that legalization of recreational marijuana use significantly reduced perceptions of marijuana’s harmfulness by 14% and 16% among eighth and 10th graders and increased their past-month marijuana use by 2% and 4% in Washington state but not in Colorado.
Among states without legalized marijuana use, the perceived harmfulness also decreased by 5% and 7% for students in the two grades, but marijuana use decreased by 1.3% and 0.9%. Among older adolescents in Washington state and all adolescents surveyed in Colorado, there were no changes in perceived harmfulness or marijuana use in the month after legalization.
The investigators attribute the lack of change in attitudes and marijuana use among teens in Colorado after legalization to a more robust commercialization effort prior to the law taking effect.
Colorado had very developed medical marijuana dispensary systems before recreational use became legal, with substantial advertising which youth were exposed to. Colorado also had lower rates of perceived harmfulness and higher rates of use compared to Washington state and other states where recreational use is not legal.
“While legalization for recreational purposes is currently limited to adults, potential impacts on adolescent marijuana use are of particular concern,” said Magdalena Cerdá, an epidemiologist with the UC Davis Violence Prevention Research Program and first author of the study.
“Some adolescents who try marijuana will go on to chronic use, with an accompanying range of adverse outcomes, from cognitive impairment to downward social mobility, financial, work-related and relationship difficulties. We need to better understand the impact of recreational marijuana use so we’re better prepared to prevent adverse consequences among the most vulnerable sectors of the population,” Cerdá said.
The potential effect of legalizing marijuana for recreational use has been a topic of considerable debate since Washington and Colorado first legalized its use for adults in 2012. Alaska, Oregon and Washington, DC, followed suit in 2014, and voters in California, Massachusetts and Nevada approved recreational use this past November.