Cannabis legalization in the US. Where do we go from here?

1 Department of Epidemiology, Mailman School of Public Health, New York, NY, USA. Submitted Apr 11 2022, accepted for publication Apr 14 2022. Suggested citation: Martins SS, Levy NS, Bruzelius E, Segura LE. Cannabis legalization in the US. Where do we go from here? Trends Psychiatry Psychother. 2022;44(Suppl 1):e20220001. http://doi.org/10.47626/2237-6089-2022-0001 Cannabis legalization in the US. Where do we go from here?

Silvia S. Martins, 1 Natalie S. Levy, 1 Emilie Bruzelius, 1 Luis E. Segura 1 Cannabis is the most commonly used illegal drug globally. [1][2][3][4] Use often begins in adolescence [5][6][7] and heavy adolescent and young adult cannabis use is associated with serious negative consequences. 5,6,[8][9][10][11] For example, longitudinal studies show that weekly cannabis use and development of abuse or dependence in adolescence are associated with increased risk of school dropout, truancy, and unemployment. 10 Cannabis use has also been associated with depression, anxiety disorder, and suicidal ideation across the life course, and may be associated with other adverse outcomes in certain populations or settings. [12][13][14][15] Cannabis use was legal in the United States (US) in the 1800s and was commonly used therapeutically. [16][17][18] However, following the development of synthetic painkillers 19 and a period of considerable media attention to cannabis-related violence, Congress outlawed recreational use in 1937 and made access for medical use burdensome. 16,17,19 In 1970, cannabis was defined federally as a Schedule I substance with "no… accepted medical use" effectively making all cannabis use illegal. 20 However, in 1996, California passed Proposition 215, allowing for medical use of cannabis in the state. 21 Since then, cannabis laws have changed rapidly across the US. As of January 2022, 18 states and Washington (DC) had fully legalized cannabis use for adults aged ≥ 21 years and an additional 18 states had legalized medical cannabis. 22 Opponents of cannabis legalization suggest that it would increase the availability of cannabis, making its use and attendant negative consequences more widespread. 23 The possibility of increased cannabis use among youth is of particular concern. In this article we will present evidence from several of our research group's studies evaluating the relationship between enactment of medical and/or recreational cannabis laws and cannabis use outcomes in the US. We will also briefly present data from other research teams on the role of cannabis dispensaries in changing patterns of cannabis use.

Recent trends in cannabis use in the US overall and by cannabis legalization status
Our work has identified differing trends in cannabis use by demographic characteristics. While cannabis use is generally more common among men than women, 24 the prevalence of use increased for both groups from 2002 to 2014. However, we further found that increases were greater for men (+4.0%) than for women (+2.7%), leading to a widening of the gender gap over time (p < 0.001). This divergence was primarily driven by increased prevalence among men in the lowest income level (+6.2%) from 2007 to 2014. 25 Among women, trends also suggest increased cannabis use during pregnancy. We found that between 2002-2014, past month use among pregnant women increased 62% nationally. 26 Our work has also uncovered age differences in cannabis use, including significant increases in the prevalence of past-year cannabis use among older adults from 2006/07 to 2012/13, with a 57.8% relative increase for adults aged 50-64 (linear trend P < 0.001) and a 250% relative increase for those aged ≥ 65 (linear trend P = 0.002). 27 We have also found that

Medical cannabis laws and cannabis use outcomes
Using National Surveys of Drug Use and Health (NSDUH) restricted-use individual-level data, we found that from 2004 to 2013, states that passed medical cannabis laws had higher prevalence of pastmonth cannabis use before passing medical cannabis laws compared with states that never passed these laws. 29 We also found evidence of increases in both the prevalence of past-month cannabis use and the prevalence of perceiving cannabis as easily available after the passage of medical cannabis laws among those 26 and older. Comparing the period after passage of medical cannabis laws with the period before passage, the adjusted odds ratio (aOR) for past-month cannabis use was 1.24 (95% confidence interval [95%CI] 1.16-1.31) and for perceived availability was 1.11 (95%CI 1.07-1.15). However, no differences in prevalence were observed for younger age groups.
We have also used NSDUH data to examine whether the age-specific impact of medical cannabis laws on the prevalence of cannabis use, daily cannabis use, and past-year cannabis use disorder varies by gender.
We found that among those 26+, past-month cannabis use increased significantly for men from 7.0% before to 8.7% after enactment of medical cannabis laws (+1.7%, p < 0.001) and for women from 3.1% before to 4.3% after enactment (+1.1%, p = 0.013). In this age group, daily cannabis use among those reporting past-month cannabis use also increased significantly after enactment for both genders (men: 16.3% to 19.1%, +2.8 %, p = 0.014; women: 9.2% to 12.7%, +3.4%, p = 0.003). We did not observe any significant increases in past-year cannabis use disorder prevalence for any age or gender group after medical cannabis law enactment. 30 The empirical findings from our studies were also supported by a systematic review of articles testing quantitative differences in cannabis use among 10 to 25-year-olds following liberalization of cannabis policy (decriminalization and legalization). 31 Two independent readers identified 41 original research reports for review. The highest quality studies found no evidence of a change in medical cannabis use following cannabis decriminalization or legalization for medical purposes.
A slight increase in recreational use was observed for adolescents and youth after recreational legalization.
An implicit assumption of all studies investigating the effects of medical cannabis laws on cannabis use is that all individuals residing in a state are aware of state policies and can adjust their behavior accordingly. We interrogated this assumption and found that from 2004-2013, an average of 68.6% of individuals in states that never passed medical cannabis laws correctly identified that their state had not legalized cannabis for medical use. In states that ever passed a medical cannabis law, 67.7% correctly identified that their state did not have medical cannabis laws before medical cannabis law enactment, while only 44.8% correctly identified that their state had a medical cannabis law after enactment of the law. 32 We also found that adolescents had lower medical cannabis law knowledge than adults, consistent with earlier findings that the effects of medical cannabis law on cannabis use were restricted to adults only.
Our research has also explored how enactment of different types of medical cannabis law programs impact subsequent patterns of cannabis use. We compared changes in the prevalence of cannabis use, frequent cannabis use, and cannabis use disorder in states with highly regulated ("medicalized") medical cannabis law programs to those in states with "nonmedical" medical cannabis law programs. We found that more loosely-regulated medical cannabis law programs were associated with increases in pastmonth cannabis use and frequent cannabis use among adults 26+ after medical cannabis laws were enacted. No increases in cannabis use prevalence were observed in states with more highly regulated medical cannabis law programs. Additionally, there were no increases in adolescent or young adult cannabis use outcomes following medical cannabis law passage, irrespective of program type. 33 Relatedly, we also explored how the stringency of medical cannabis law regulations affects enrollment rates on medical cannabis programs. We found that fourteen of the twenty-four programs assessed were nonmedical (more loosely regulated) and collectively

Recreational cannabis laws and cannabis use outcomes
More recently, our team has turned its attention to expanding the limited available research on the effects of recreational cannabis laws on cannabis use outcomes.
Using 2008-2016 NSDUH data, we found that similarly to medical cannabis laws, changes in cannabis outcomes were primarily only observed for those 26  While the significant association between recreational cannabis laws and cannabis use disorder in this age group warrants additional interrogation, the increasing prevalence of cannabis use disorder among those 12-17 years of age is concerning regardless of its cause and should continue to be monitored.
We have also pursued studies exploring how patterns of cannabis use following recreational cannabis law enactment may differ by race and ethnicity.
We found that compared with the period before recreational cannabis law enactment and after medical cannabis enactment, the odds of past-year cannabis use after enactment increased among Hispanic (aOR:  43 Our study was the first study to explore racial/ethnic-specific and age-stratified associations with recreational cannabis laws, particularly focusing on the period after enactment of preexisting medical cannabis laws. Separating out the effects of these laws is of utmost importance since studies conducted prior to recreational cannabis law enactment identified differential trends in cannabis outcomes over time by race/ethnicity. In an effort to minimize racial inequalities in cannabis legislation enforcement, future studies will need to examine patterns of cannabis use in the context of persistent racial/ethnic disparities in cannabis arrests and incarceration. 44,45 Cannabis dispensaries and cannabis use A growing body of research focuses on intended and unintended effects of cannabis use, consequences of cannabis availability, and the effects of dispensary programs on local communities. Interestingly, increased density of dispensaries has been associated with increased cannabis hospitalizations, 46 poison center calls, 47 and a higher likelihood of adolescent cannabis use. 48 Budney and Borodovsky 49 argue for more stringent regulations related to levels of access created by medical and recreational dispensaries, particularly cannabis product potency and how cannabis products are consumed. As more states adopt recreational cannabis laws and more time has passed since their enactment, additional studies will be needed to explore the persistent effects of legalization.

Limitations
The studies described above are not without limitations. First, almost all of the analyses described here relied on self-reported cannabis use and the social desirability of reporting cannabis use and consequent measurement error may have changed differentially by state medical and recreational cannabis law status.
In the NSDUH, the dataset used for most of the studies described here, the use of computer-assisted interviews reduces these concerns. 50

Conclusion
In conclusion, existing US studies have shown increases in cannabis use outcomes following the enactment of medical and recreational cannabis laws, but these increases are limited to adults. To date, no changes in the prevalence of any cannabis use or daily/ near daily use have been observed among adolescents after medical or recreational legalization. 30,40,[51][52][53] A recent study 40 found increases in cannabis use disorder after recreational legalization among 12 to 17-year-olds who used cannabis in the past year, from 22.8% to 27.2%; however, the authors cautioned that associations between recreational cannabis law passage and these increases could reasonably be attributed to random error or unmeasured confounding. Additional work is needed to replicate and interrogate whether this change is attributable to legalization, particularly as the prevalence of cannabis use in this age group declined from 2002-2018. 1 Ultimately, accurate empirical evidence, rather than ideology, should guide decision-making around cannabis policies. At present, there is little evidence to suggest widespread negative effects on cannabis use outcomes following the enactment of medical or recreational cannabis laws. Epidemiologic research is ongoing on the effects of cannabis policies, as well as on variations in such policies, and longitudinal studies with longer follow-up times are sorely needed.