Does Legalized Marijuana Result in More Teen Use?

A new study on teen cannabis use tries to cut through the politics.

Posted Apr 20, 2017

The debate over legalizing marijuana continues to be heard at many state capitols, including in my home state of Vermont. Consistently, one of the biggest flashpoints has to do with whether or not legalization would increase cannabis use among adolescents, something that even most legalization advocates do not want to see. This is why many advocates have been championing some data from Colorado that generally indicate that there has not been an increase in youth use in that state since cannabis was legalized in 2014. Those more concerned about legalization, however, have pointed out that a) these numbers generally don’t compare Colorado to anything, and b) a lot more states other than Colorado have now legalized marijuana. What about them?

Just a few months ago, perhaps one of the best scientific studies on the subject was published in the journal JAMA Pediatrics. What gave this study some additional gravitas was that it looked at rates of teen cannabis use in both Colorado and Washington state (the other state that legalized in 2014), and it used data from nonlegalizing states as a comparison. The main variables of interest were self-reported cannabis use in the past month and a rating of perceived harmfulness of marijuana. These items came from a well-known longitudinal survey called the Monitoring the Future Study which queried over a quarter million youth in 8th, 10th, and 12th grade. Comparison were made on rates for the period right before and after legalization.

So far so good, right? Things seems well teed up to provide that more definitive answer we’ve all been looking for. Unfortunately, very different results were obtained for Washington state relative to Colorado. In Washington, perceived harm from cannabis fell while past month usage significantly increased for both 8th and 10th graders, compared to non-legalizing states. Specifically, past-month usage increased in 8th graders from 6.2% to 8.2% while in 10th graders it rose from 16.2% to 20.3%. These increases compared to a slight decrease in use for nonlegalizing states across the same time period. For Colorado, however, no significant differences were found in either usage or perceived harmfulness when compared to nonlegalizing states.

The authors of the study seemed at a bit of a loss to explain the discrepancy, but hypothesized that one potential reason was that Colorado already had a very active medical marijuana presence prior to recreational legalization which may have resulted in the teen increase having already occurred by 2014. Indeed, data support this view. Washington, by contrast, did not have such a developed industry prior to legalization and as a result saw more of a culture shift after legalization in 2014.

These speculations aside, information about teen marijuana use relative to legalization status has been a fascinating study in how data can be cherry picked and interpreted to fit whatever conclusions one would like to make. Marijuana use among Colorado teens does appear relatively flat recently, yet during the same time period Colorado’s ranking in rates of teen cannabis use has “risen” to #1 in the country, mainly because non-legalizing states have seen their rates drop slightly. This has led to dueling headlines emphasizing one of these aspects over another.

Even the bottom line of “we have no idea what will happen,” seems to be a platform from which to move in different directions. To some, it’s further confirmation that the sky isn’t falling and that we can rest easy knowing that legalization does not result in a clear uptick in adolescent use. To others, the same data is additional ammunition for the idea that we still don’t really know what is going on and should therefore move very cautiously into this unknown territory where it will be very difficult to change course.

@copyright by David Rettew, MD

David Rettew is author of Child Temperament: New Thinking About the Boundary Between Traits and Illness and a child psychiatrist in the psychiatry and pediatrics departments at the University of Vermont College of Medicine.

Follow him at @PediPsych and like PediPsych on Facebook.


Cerda M, Wall M, et al. (2017).  Association of state recreational marijuana laws with adolescent Marijuana use. JAMA Pediatrics; 171(2): 142-149.