Marijuana study has limitations

Jun 01, 16 Marijuana study has limitations

The Journal of the American Academy of Child & Adolescent Psychiatry (JAACAP), recently published a study claiming a significant drop in marijuana-related problems among teenagers, such as addiction and having trouble at school.

As with all review of scientific research, it’s important to understand a study’s limitations and how it fits into larger context. It is also to important to guard against news coverage and interpretations of research that make claims the data do not support.

Which brings us back to that study published in this month’s edition of JAACAP and the insistence coming from pro-marijuana-legalization pundits and sources that the findings are evidence that marijuana legalization is not harmful to youth. Indeed, an editorial responding to the research in the same edition of JAACAP states “no such inference is warranted.”

Among the limitations of this study:

  • The study combines all states and does not differentiate among those with legal and/or less restrictive “medical” marijuana policies and those that have not sanctioned the drug’s use at all.
  • The study examines data from 2002 to 2013 — a period just before retail sales and all of the marketing and advertising accompanying them started in 2014.
  • Data show marijuana use declined from 2002 to 2009, but increased afterwards. It’s important to note that late 2009 was the start of the boom in so-called “medical” marijuana dispensaries.
  • This study contradicts data from the U.S. Department of Health and Human Services, the National Survey on Drug Use and Health and the federally funded Monitoring the Future Study — all of which show an increase in kids using marijuana and needing treatment.
  • Finally, as Dr. Christian Hopfer, my colleague at the University of Colorado writes in his counterpoint editorial, it is possible “a decrease in conduct problems accounted for the decrease in the development of marijuana use disorders. Although this is not proof of a causal effect, one potential inference is that as marijuana use becomes more acceptable, more individuals without conduct or adult antisocial problems will use marijuana and that the risk of developing a use disorder is lower in individuals without comorbid conduct or adult antisocial problems.”

    Marijuana-related problems involving youth in states that have sanctioned the drug are mounting — as detailed here by the nonprofit organization Smart Approaches to Marijuana (I serve as a science advisor to learnabousam.org.). Colorado is the top state in the nation for adolescent marijuana use. The World Health Organization also has issued a report about marijuana’s impact on adolescents. It found harms to “several components of cognitive function, with the most robust effects on short term episodic and working memory, planning and decision-making, response speed, accuracy and latency.” The report also detailed studies that found “heavy cannabis use over several decades produced substantial declines in cognitive performance that may not be wholly reversible… (and) an association between poorer verbal memory and sustained daily use of cannabis throughout adult life.”

    Dr. Christian Thurstone is an associate professor at the University of Colorado, where he serves as director of medical training for the addiction psychiatry fellowship program. He is also medical director of one of Colorado’s largest adolescent addiction-treatment programs.

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