US Adult Illicit Cannabis Use, Cannabis Use Disorder, and Medical Marijuana Laws 1991-1992 to 2012-2013
Deborah S. Hasin, Aaron L. Sarvet, Magdalena Cerda, Katherine M. Keyes, Malka Stohl, Sandro Galea, Melanie M. Wall
JAMA Psychiatry, 2017, 74, (6), 579–610.
Are US state medical marijuana laws one of the underlying factors for increases in risk for adult cannabis use and cannabis use disorders seen since the early 1990s?
In this analysis using US national survey data collected in 1991-1992, 2001-2002, and 2012-2013 from 118 497 participants, the risk for cannabis use and cannabis use disorders increased at a significantly greater rate in states that passed medical marijuana laws than in states that did not.
Possible adverse consequences of illicit cannabis use due to more permissive state cannabis laws should receive consideration by voters, legislators, and policy and health care professionals, with appropriate health care planning as such laws change.
Over the last 25 years, illicit cannabis use and cannabis use disorders have increased among US adults, and 28 states have passed medical marijuana laws (MML). Little is known about MML and adult illicit cannabis use or cannabis use disorders considered over time.
To present national data on state MML and degree of change in the prevalence of cannabis use and disorders.
Design, Participants, and Setting
Differences in the degree of change between those living in MML states and other states were examined using 3 cross-sectional US adult surveys: the National Longitudinal Alcohol Epidemiologic Survey (NLAES; 1991-1992), the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC; 2001-2002), and the National Epidemiologic Survey on Alcohol and Related Conditions–III (NESARC-III; 2012-2013). Early-MML states passed MML between NLAES and NESARC (“earlier period”). Late-MML states passed MML between NESARC and NESARC-III (“later period”).
Main Outcomes and Measures
Past-year illicit cannabis use and DSM–IV cannabis use disorder.
Overall, from 1991-1992 to 2012-2013, illicit cannabis use increased significantly more in states that passed MML than in other states (1.4–percentage point more; SE, 0.5; P = .004), as did cannabis use disorders (0.7–percentage point more; SE, 0.3; P = .03). In the earlier period, illicit cannabis use and disorders decreased similarly in non-MML states and in California (where prevalence was much higher to start with). In contrast, in remaining early-MML states, the prevalence of use and disorders increased. Remaining early-MML and non-MML states differed significantly for use (by 2.5 percentage points; SE, 0.9; P = .004) and disorder (1.1 percentage points; SE, 0.5; P = .02). In the later period, illicit use increased by the following percentage points: never-MML states, 3.5 (SE, 0.5); California, 5.3 (SE, 1.0); Colorado, 7.0 (SE, 1.6); other early-MML states, 2.6 (SE, 0.9); and late-MML states, 5.1 (SE, 0.8). Compared with never-MML states, increases in use were significantly greater in late-MML states (1.6–percentage point more; SE, 0.6; P = .01), California (1.8–percentage point more; SE, 0.9; P = .04), and Colorado (3.5–percentage point more; SE, 1.5; P = .03). Increases in cannabis use disorder, which was less prevalent, were smaller but followed similar patterns descriptively, with change greater than never-MML states in California (1.0–percentage point more; SE, 0.5; P = .06) and Colorado (1.6–percentage point more; SE, 0.8; P = .04).
Conclusions and Relevance
Medical marijuana laws appear to have contributed to increased prevalence of illicit cannabis use and cannabis use disorders. State-specific policy changes may also have played a role. While medical marijuana may help some, cannabis-related health consequences associated with changes in state marijuana laws should receive consideration by health care professionals and the public.
Over the last 20 years, laws and attitudes regarding cannabis have changed. As of November 2016, 28 states have passed medical marijuana laws (MML). Many adults now favor legalizing recreational use, and fewer view cannabis as risky. Despite this view, while some can use cannabis without harm, potential consequences include impaired functioning, vehicle crashes, emergency department visits, psychiatric symptoms, and addiction. Over time, the prevalence of adult illicit use and related consequences has increased. Thus, identifying factors underlying increased adult illicit use is important. State MML may be one such factor.
Little is known about MML and adult cannabis outcomes. Two national studies showed greater use and DSM–IV–diagnosed disorders in MML states but did not examine differences before and after MML. One national study did so, finding increased post-MML cannabis use and cannabis disorders. However, this study only addressed 2004 to 2012, adults 20 years and older, and 10 states that changed MML status. To our knowledge, no study of differences before and after MML has used adult national data predating all MML, differentiated between earlier and more recent periods, or separately examined particular states. Differences between states that passed MML early vs late are important because the national normative context differed for early-MML states, when few such laws existed, and late-MML states, enacted when more states had MML. Also, earlier data can show if trends in cannabis use and disorder in late-passing states began prior to their MML. Further, California and Colorado warrant separate, secondary examination. In 1996, when California passed the first MML, its cannabis rates were higher than other states, and thus its MML may have had little additional effect. Colorado (MML passed in 2000) experienced unique policy changes in 2009-2010 (eAppendix 1 in the Supplement) followed by increases in medical user applications from 500 per month to greater than 10 000 per month and from no known dispensaries to greater than 900, potentially exerting additional impact on cannabis outcomes during the later period.
We examined MML, illicit cannabis use, and cannabis use disorders in 3 cross-sectional adult surveys: the 1991-1992 National Longitudinal Alcohol Epidemiologic Survey (NLAES), the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), and the 2012-2013 National Epidemiologic Survey on Alcohol and Related Conditions–III (NESARC-III). Over this period, the national context for MML changed. In 1991-1992, no Americans lived in MML states; in 2001, 18.9% lived in MML states, and in 2012, more than one-third (34.3%) lived in MML states. We therefore addressed 3 questions. First, between 1991-1992 and 2012-2013 (the overall study period), were changes in the prevalence of illicit cannabis use and disorders greater in states that ever had MML vs never had MML? Second, between 1991-1992 and 2001-2002 (for convenience, termed the earlier period), did changes in prevalence differ between states that did and did not pass MML during this time, including and excluding California? Third, between 2001-2002 and 2012-2013 (for convenience, termed the later period), did changes in prevalence differ between never-MML states, states passing MML during the earlier period, and states passing MML during the later period? In investigating the later period, we again kept California separate and also separated Colorado, given its 2009-2010 changes.