The legalization of marijuana for recreational purposes in some U.S. states is currently limited
to adults. However, the potential impacts on adolescent marijuana use are of
Marijuana use significantly increased and its perceived harm
decreased among eighth- and 10th-graders in Washington state following
enactment of recreational marijuana laws, suggested a UC Davis and
Columbia University Mailman School of Public Health to be published
online in JAMA Pediatrics
. There was no change in use or perceived harm among 12th graders or among similar grades in Colorado.
‘Legalization of recreational marijuana use significantly reduced perceptions of marijuana's harmfulness by eighth and 10th graders and increased their past-month marijuana use.’
The journal also posted editorials on the impact of legalization of marijuana by Wayne Hall and Megan Weier and by Alain Joffe.
The authors believe the study
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 researchers compared data on the perceived harmfulness of
marijuana use to health and self-reported marijuana use for nearly
254,000 students in the eighth, 10th and 12th grades in Colorado,
Washington and 45 other contiguous U.S. states who participated in the
Monitoring the Future survey.
The survey measures drug, alcohol and cigarette use and related
attitudes among adolescent students nationwide. The authors compared
Washington and Colorado with 45 other states in the contiguous U.S. that
did not legalize recreational marijuana use. In a sensitivity analysis,
they also compared Washington and Colorado data with 20 states with
medical marijuana laws but no recreational marijuana laws; results were
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.
Magdalena Cerdá, an epidemiologist with the UC
Davis Violence Prevention Research Program and first author of the
study, said, "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."
While more targeted research is needed to determine the influence of
legalized recreational marijuana use among adolescents and how well the
Washington state and Colorado experiences can be generalized to the
rest of the U.S., the authors believe that states considering legalized
recreational use may also want to consider investing in evidence-based
substance abuse prevention programs for adolescents.
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, D.C., followed suit in 2014, and voters in California,
Massachusetts and Nevada approved recreational use this past November.
"The perceived harmfulness of marijuana has declined sharply in the
U.S. in the last few years, despite the fact that there are adverse
consequences associated with marijuana use in some adults and in
adolescents," said Deborah Hasin, a professor of epidemiology at
Columbia University's Mailman School of Public Health and in psychiatry
at Columbia University and principal investigator of the study.
"Epidemiologic monitoring of these consequences as more states
legalize recreational use, and public education about potential health
consequences, are important to protect public health," Hasin said.
Cerdá noted that the study suggests that legalization of marijuana
in Washington reduced stigma and perceived risk of use, which could
explain why younger adolescents are using more marijuana after
"Other potential reasons for the increase in use include increased
access to marijuana through third-party purchases, and lower price,"
Cerdá said. "Older adolescents may also have had their attitudes and
beliefs about marijuana formed before recreational marijuana use was
legalized, making it less likely their use would change after