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Original Investigation
November 13, 2019

Association Between Recreational Marijuana Legalization in the United States and Changes in Marijuana Use and Cannabis Use Disorder From 2008 to 2016

Author Affiliations
  • 1Division of Epidemiology, Department of Population Health, New York University School of Medicine, New York
  • 2Violence Prevention Research Program, Department of Emergency Medicine, University of California, Davis, Sacramento
  • 3Department of Biostatistics, Columbia University Mailman School of Public Health, New York, New York
  • 4Department of Epidemiology, Columbia University Mailman School of Public Health, New York, New York
  • 5Division of Translational Epidemiology, Vagelos College of Physicians and Surgeons, Columbia University, New York, New York
  • 6Division of Translational Epidemiology, New York State Psychiatric Institute, New York
JAMA Psychiatry. Published online November 13, 2019. doi:https://doi.org/10.1001/jamapsychiatry.2019.3254
Key Points

Question  How did marijuana use and cannabis use disorder change during 2008 to 2016 after the legalization of recreational marijuana in the United States?

Findings  In this multilevel, difference-in-difference survey study with 505 796 respondents comparing marijuana use before and after the legalization of recreational marijuana in the United States, the proportion of respondents aged 12 to 17 years reporting cannabis use disorder increased from 2.18% to 2.72%, while the proportion of respondents 26 years or older reporting frequent marijuana use increased from 2.13% to 2.62% and those with cannabis use disorder, from 0.90% to 1.23%.

Meaning  This study’s findings suggest that possible increases in the risk for cannabis use disorder among adolescent users and increases in frequent use and cannabis use disorder among adults after legalization of recreational marijuana use may raise public health concerns and warrant ongoing study.

Abstract

Importance  Little is known about changes in marijuana use and cannabis use disorder (CUD) after recreational marijuana legalization (RML).

Objectives  To examine the associations between RML enactment and changes in marijuana use, frequent use, and CUD in the United States from 2008 to 2016.

Design, Setting, and Participants  This survey study used repeated cross-sectional survey data from the National Survey on Drug Use and Health (2008-2016) conducted in the United States among participants in the age groups of 12 to 17, 18 to 25, and 26 years or older.

Interventions  Multilevel logistic regression models were fit to obtain estimates of before-vs-after changes in marijuana use among respondents in states enacting RML compared to changes in other states.

Main Outcomes and Measures  Self-reported past-month marijuana use, past-month frequent marijuana use, past-month frequent use among past-month users, past-year CUD, and past-year CUD among past-year users.

Results  The study included 505 796 respondents consisting of 51.51% females and 77.24% participants 26 years or older. Among the total, 65.43% were white, 11.90% black, 15.36% Hispanic, and 7.31% of other race/ethnicity. Among respondents aged 12 to 17 years, past-year CUD increased from 2.18% to 2.72% after RML enactment, a 25% higher increase than that for the same age group in states that did not enact RML (odds ratio [OR], 1.25; 95% CI, 1.01-1.55). Among past-year marijuana users in this age group, CUD increased from 22.80% to 27.20% (OR, 1.27; 95% CI, 1.01-1.59). Unmeasured confounders would need to be more prevalent in RML states and increase the risk of cannabis use by 1.08 to 1.11 times to explain observed results, indicating results that are sensitive to omitted variables. No associations were found among the respondents aged 18 to 25 years. Among respondents 26 years or older, past-month marijuana use after RML enactment increased from 5.65% to 7.10% (OR, 1.28; 95% CI, 1.16-1.40), past-month frequent use from 2.13% to 2.62% (OR, 1.24; 95% CI, 1.08-1.41), and past-year CUD from 0.90% to 1.23% (OR, 1.36; 95% CI, 1.08-1.71); these results were more robust to unmeasured confounding. Among marijuana users in this age group, past-month frequent marijuana use and past-year CUD did not increase after RML enactment.

Conclusions and Relevance  This study’s findings suggest that although marijuana legalization advanced social justice goals, the small post-RML increase in risk for CUD among respondents aged 12 to 17 years and increased frequent use and CUD among adults 26 years or older in this study are a potential public health concern. To undertake prevention efforts, further studies are warranted to assess how these increases occur and to identify subpopulations that may be especially vulnerable.

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    2 Comments for this article
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    An Obvious Outcome?
    Raymond Small, MD, MPH | Physicianet Consulting Group, LTD
    Is anyone actually surprised by the findings of this study/survey? The conclusions seem rather obvious to my way of thinking. Make a once illicit substance readily available for purchase and void of prior criminality--with its consequences--and more and more people are going to use and/or abuse it, invariably magnifying negative aspects of usage; warranting public health concerns. Consider stats purporting that the rates of opioid abuse and the morbidity and mortality from overdosage have decreased notably in states that have legalized recreational cannabis. Is this not a net positive; a lesser of two evils in favor of THC legalization? Calculation of a "risk versus benefit" ratio should be utilized in this still controversial and polarizing subject as much as it is in more mainstream medicine and public health agencies.
    CONFLICT OF INTEREST: None Reported
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    Prohibition and consumption
    Silver Damsen, PhD | University of Illinois, Urbana-Champaign
    I'm surprised, but then not that there is little thought about the fact that the 17-12 year-old group can't purchase legal marijuana in the first place. Thus, making marijuana more readily available through legal channels for those over 21 shouldn't impact those under 18. Teens purchased their marijuana illegally before adult legalization and are still purchasing it illegally after adult legalization. The cost of legal marijuana also tends to be significantly higher than those purchased through illegal means. So, it would not seem at all likely that adults are purchasing legal marijuana that they are then re-selling illegally to teens.

    This statistic alone should challenge the hypothesis that making a drug legal increases the chances that it will be abused. The increase is also so small as to be questionable as statistically significant in the first place.

    Thus, it makes more sense to at least consider other variables as contributing to the increase in over-consumption (that is if we assume the change is even statistically significant). If one looks at the history of prohibition, the pattern is that the more a drug is prohibited, the more dangerous its consumption tends to be. Thus, an overall increase in prohibition advertising and Just Say No campaigns are also likely contributers, as would be stress in society. To understand the last aspect Bruce Alexander's Rat Park experiments would be required reading.

    I hate to have to point this out to professional researchers, and that I do shows the pathetic state of research on drug consumption, but far too much research, including this piece here, does not look at the social history of drug consumption that prior to prohibition about 100 years ago that opioids, coca (the original form of cocaine), and marijuana were safely consumed for thousands of years. Thus, a more useful study would be what was going on around a hundred years ago that worked to create prohibition and how has prohibition impacted consumption?

    That these researchers seem entirely unfamiliar with the the data that says that prohibition increases dangerous consumption but doesn't decrease overall use. This is because the normal Supply and Demand model that justifies prohibition doesn't apply to drugs because the Demand for drugs is inelastic. Thus, while in normal conditions if the price for a commodity is increased, the Demand will go down, but this doesn't hold for drugs. Rather, if the cost is increased it just means that those that purchase the drug will suffer more to acquire it. Curiously, overall and once society has stabilized after making a formally illegal drug legal again, not only dangerous consumption but overall consumption tends to go down. However, true enough it would not be realistic to expect it to stop entirely.

    Also, relevant would be to compare this increase (which again I'm not seeing as that statistically significant) to what has been reported as the increase in alcohol over-use after the end of prohibition. For a time, consumption of alcohol showed signs of over-consumption, but this stabilized over time.

    But most relevant of all is that prohibition doesn't work. We have a hundred years of it failing to show that it doesn't work. And this study seems badly constructed from the outset simply by including those that can't purchase legal marijuana and not even attempting to discuss or define that for teens drugs will be illegal even if all prohibition ends for adults. However, it does point out that prohibition itself doesn't keep someone from getting a drug they want.
    CONFLICT OF INTEREST: None Reported
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