A team of investigators from Columbia University, the University of California at Davis, the University of Michigan, and Boston University evaluated whether students’ perceptions of marijuana had changed following the legalization of medical cannabis in their states.
Authors reported that the passage of medical cannabis laws was associated with an increase in the perceived harmfulness of marijuana among 8th graders, as well as a significant decline in their self-reported use of the substance. A similar change in the perception of cannabis was not observed in older adolescents.
Investigators concluded: “[A]mong 8th grade students, in states with MML (medical marijuana laws) compared to those without, perceived harmfulness increased after MML were passed, a result contrary to the overall national time trend. These findings indicate that in a national landscape of decreasing perceived harmfulness, young adolescents in states that pass MML have a lower overall decrease in perceived harmfulness than adolescents in states without MML. Given that perceived harmfulness of marijuana is strongly associated with less use of marijuana, this indicates that over time, young adolescents in MML states could be expected to be less likely to use marijuana than adolescents in those states pre-passage.”
Separate data published in 2015 in The American Journal of Drug and Alcohol Abuse similarly determined that the proportion of young adolescents who report that they strongly disapprove of marijuana use has risen over the past decade.
Full text of the study, “Medical marijuana laws, marijuana use and perceived harmfulness: 1991-2014,” appears in Addiction.