Teen Marijuana Use before & after Legalizing Recreational Marijuana

Recreational marijuana use became legal in four more states this past November. It is now legal to possess, use, and grow a small amount of marijuana in California, Nevada, Massachusetts, Maine, Alaska, DC (currently on hold), Colorado, Oregon, and Washington. Medical marijuana use is legal in 28 states and DC, more than half of all US states. These historical shifts in marijuana policy have developed in a short number of years.


How are the new recreational policies affecting teen use of marijuana? Researchers from universities across the US, including ISR at UM, just published a study in JAMA Pediatrics focusing on the 2012 legalization of recreational use in Washington and Colorado. The investigators analyzed what adolescents said about how harmful they think marijuana is and about their own marijuana use, comparing before and after legalization.


The study used data gathered each year from 8th, 10th, and 12th graders across the US. A total of 253,902 students were surveyed from 2010 to 2015 as part of the Monitoring the Future project (MTF). MTF is a national, annual, cross-sectional survey of students in the contiguous US. The study compared perceived harmfulness of marijuana use and marijuana use among teens in Washington and Colorado prior to recreational marijuana legalization (2010-2012) with post-legalization (2013-2015). It also compared these results with the trends in other states that did not legalize recreational marijuana use during this period. Perceived harmfulness was counted if students saw great or moderate risk to health from smoking marijuana occasionally. Marijuana use was measured as any marijuana use in the past 30 days.


Results: In Washington, fewer 8th and 10th graders surveyed from 2013 to 2015 saw marijuana use as harmful, compared to those surveyed from 2010 to 2012. In addition, marijuana use itself increased. In particular, from the 2010-2012 period to the 2013-2015 period, perceived harmfulness declined 14% among 8th graders and 16% among 10th graders; marijuana use increased 2% (8th grade) and 4% (10th grade). States that did not legalize recreational marijuana use also saw declines in perceived harmfulness but by much smaller degrees: 5% among 8th graders and 7% among 10th graders. In the non-legalizing states marijuana use actually decreased by a little over 1% in 8th grade and just under 1% in 10th grade over the same period. The changes found in Washington among 8th and 10th graders were not found among 12th graders there. The changes were also not found in Colorado, where there were no significant differences in perceived harmfulness or marijuana use for any of the three grades.


In sum, after recreational marijuana use was legalized in Washington, perceived harmfulness of marijuana use decreased and marijuana use increased among 8th and 10th graders. Colorado teens did not show changes in perceived harmfulness or marijuana use after legalization. The findings may cautiously point to the importance of prevention programs targeting adolescent substance use in states with legal recreational marijuana use.


Cerda, M., Wall, M., Feng, T., Keyes, K.M., Sarvet, A., Schulenberg, J., O’Malley, P.M., Pacula, R.L., Galea, S., & Hasin, D.S. (2016). Association of state recreational marijuana laws with adolescent marijuana use. JAMA Pediatrics, Online. doi: 10.1001/jamapediatrics.2016.3624. https://www.ncbi.nlm.nih.gov/pubmed/28027345