Building Evidence-Based Prevention Mechanisms Into Cannabis Legalization Policy and Regulations

Cannabis (“marijuana”) refers to the crude and varying cannabinoid components of several cannabis plant varietals, including the two most common varietals consumed in the United States, Cannabis indica and Cannabis sativa. Cannabis has gone through varying phases of legality in the United States; however, it has been illegal under federal law since enactment of the Controlled Substances Act of 1970 (Pub L No. 91-513), where it remains classified as a Schedule I drug (i.e., no currently accepted medical use, high potential for abuse, and lack of accepted safety data). Despite its federal illegality, many states have enacted more permissive cannabis laws.

As of June 2019, ten states and the District of Columbia have enacted nonmedical adult-use cannabis laws, a heterogeneous set of provisions effectively allowing adults aged 21 years or older to purchase, possess, cultivate, and consume cannabis for nonmedical adult-use (“recreational”) purposes. These state-level statutory changes have been fervently debated and there is concern that any permissive change in the legality of cannabis, including specific provisions such as allowing retail shops, may increase prevalence of cannabis use and problematic use, as well as related adverse consequences.

Cannabis is the most commonly used illicit substance by adults in the United States. Current research reports that adults’ risk perceptions of cannabis are declining while use is increasing.¹ In 2017, 9.9% of US adults aged 18 years or older reported past-30-day (“current”) cannabis use and 48.2% reported lifetime use (https://www.samhsa.gov/data/report/2017-nsduh-detailed-tables). Although cannabis use appears most harmful to youths and emerging adults, adult use is not without risk. Hasin et al. found that approximately 30% of cannabis users met criteria for a cannabis use disorder.² In addition, cannabis use risks include impaired driving, accidents and injury, cognitive impairment, psychiatric symptoms, and unknown long-term effects.^1,3

Research assessing the impacts of cannabis legalization (i.e., medical or nonmedical adult use) laws on adult cannabis use is still developing and is further complicated by law, regulatory, and other state-level differences. In a small study of Washington State parents, Kosterman et al. found that cannabis use frequency and disorders increased after nonmedical adult-use legalization.⁴ To date, most studies have assessed medical cannabis legalization enactment or implementation. Hasin et al. examined early, late, and nonadopting medical cannabis legalization states and found that cannabis use prevalence and disorders among adults increased in states that enacted medical legalization while decreasing in nonenacting states.³ Similarly, Williams et al. found that cannabis use increased among adults aged 26 years or older in permissive medical cannabis states but did not change in less permissive states.⁵ In contrast to Hasin et al., authors found that medical cannabis legalization did not have an impact on rates of cannabis use disorders, a more harmful potential effect of legalization.^3,5 Major knowledge and methodological gaps remain, including assessment of and adjustment for the heterogeneity inherent in state-led design, regulation, and enforcement of these cannabis legalization laws—as well as their effects, which may include changing social norms; patterns of use; modes of consumption; potency; substance use and mental health disorders; hospitalizations, accidents, and injury; and long-term health outcomes.

In a novel study presented in this issue of AJPH, Everson et al. (p. 1294) assess adult cannabis use outcomes by using a sophisticated methodological approach to isolate changes following implementation of a specific provision, retail cannabis market (“access”). The study’s novelty lies in its detailed account of state-specific heterogeneity, including regulation (e.g., number of permitted retail stores, seed-to-sale tracking), implementation (e.g., number and dates of active retail stores at varying locations), and community-level indicators (i.e., proximity, geospatial density, and per-capita density) for a localized assessment of access to retail cannabis on adult cannabis use behaviors. Authors report that current and frequent cannabis use grew significantly between 2009 and 2016 in Washington State, but changes were not significant until there was greater access to cannabis retailers. Specifically, cannabis use rates significantly increased for adults residing in proximity to a retail cannabis store (≤ 18.4 miles), and frequent use significantly increased for adults living very close to a store (≤ 0.8 miles). On the basis of these findings, authors suggest that policymakers consider density limits as a strategy to prevent heavy cannabis use in adults, an important proactive public health consideration for states enacting cannabis legalization.

Research on adult-use cannabis legalization is in a nascent stage and is only beginning to examine the heterogeneity in cannabis legalization efforts and potential differential impacts of varying provisions.⁶ These findings are important in light of the methods often used in the current literature assessing varying legalization change(s), which use a homogenous binary (yes or no) indicator for legalization enactment or implementation, potentially masking if varying statutes, regulation, provisions, and enforcement affect outcomes or cohorts differently. This study elucidates both the methodological limitation of binary coding of legalization and the need for more complex constructs of legalization in future studies. Furthermore, the full effects of legalization may be lagged; thus, assessing both time and variation are also key to a more comprehensive understanding. The lack of federal direction combined with state policy preceding what is collectively known scientifically necessitates innovative methods to establish a baseline and measurement of the variations inherent in state laws in a constantly evolving cannabis law landscape. As we have learned from the tobacco and alcohol industries and regulation, once science discerns differential effects of laws and specific provisions, evidence-based prevention mechanism(s) can be built into legalization policy and regulations.