Full length articleThe design of medical marijuana laws and adolescent use and heavy use of marijuana: Analysis of 45 states from 1991 to 2011
Introduction
Since 1975, marijuana has been the most widely used illicit drug among adolescents in the United States (Johnston et al., 2015). Patterns and attitudes of substance use are often established in adolescence and marijuana use typically begins in the middle to late adolescence (Hall and Degenhardt, 2009). The Monitoring in the Future survey reports that daily marijuana use increased among 8th, 10th and 12th graders from 2007 to 2011 before declining with 21.2% of 12th graders, 16.6% of 10th graders, and 6.5% of 8th graders reporting past 30-day marijuana use (Johnston et al., 2014). Keyes et al. (2016) reports that perceived harmfulness of marijuana is lower in states with MMLs. This is a grave public health concern since current research suggests that marijuana use may have both acute and long-term deleterious effects on the maturing adolescent brain (Camchong et al., 2016, Squeglia and Gray, 2016). Heavy marijuana use during adolescence could have more serious effects than use in adulthood (Jager and Ramsey, 2008) with studies of heavy adolescent marijuana users reporting learning and working memory impairments up to six weeks post cessation (Schweinsburg et al., 2008)
Marijuana cultivation and use were legal under federal and state laws throughout most of U.S. history; however, an increase in marijuana use coupled with political pressure in the early 1900s led twenty-nine states to pass laws prohibiting any sale or possession of marijuana. These state-level changes initiated federal-level prohibition marijuana policies, including the Marihuana Tax Act of 1937, making the nonmedical use of marijuana illegal (Pacula et al., 2002, Stack and Suddath, 2009) and effectively halted the medicinal use of marijuana (Belenko, 2000, Bilz, 1992, Pacula et al., 2002). The Federal Controlled Substance Act of 1970 replaced the Marihuana Tax Act, and additionally made it illegal under federal law for physicians to prescribe marijuana. Although, marijuana use, possession, cultivation, and physician prescribing has been illegal under federal law since the 1970, more recently states are challenging this prohibition.
As of September 2016, twenty-five states and the District of Columbia have enacted varying laws that effectively allow patients to use marijuana for medicinal purposes. State medical marijuana laws (MMLs) have been fervently debated. The American College of Pediatricians state concern that marijuana legalization policies may increase adolescent marijuana exposure and use, additionally stating that there is no scientific evidence that the potential healthful effects of legalizing medical marijuana use outweigh its documented adverse effects (American College of Pediatricians, 2016). Volkow et al. (2016) state concern that the efforts to normalize marijuana are being driven without regard for scientific evidence, gaps in our knowledge and the possibility of unintended consequences. Given the accelerated pace at which states are enacting similar MMLs, it is critical to have a better understanding of how previous state-enacted MMLs and their varying provisions affect adolescent marijuana use.
MMLs are enacted at the state-level, leaving great variation amongst MMLs across states in regards to the years of enactment/implementation, included provisions, the varying degree of liberalization of these provisions (e.g., medical marijuana dispensaries, number of usable ounces allowed for possession, etc.), and the fidelity of implementation and enforcement, which may theoretically affect the perceived riskiness, access, cost, and quantity of marijuana within a state. Despite these increasing concerns, there is still limited empirical information available (Wall et al., 2016).
Current research examining the effects of MMLs on adolescents shows mixed results. A literature search identified ten studies that used large national datasets to assess adolescent marijuana use amidst medical marijuana policy reform, with two studies supporting the perspective that MMLs are associated with higher marijuana use rates (Stolzenberg et al., 2016, Wall et al., 2011) and the other eight supporting the perspective that MMLs do not significantly change marijuana use rates (Anderson et al., 2014, Choo et al., 2014, Harper et al., 2012, Hasin et al., 2015, Lynne-Landsman et al., 2013, Pacula et al., 2013, Wall et al., 2016, Wen et al., 2015).
However, the analyses of the two studies finding increases in adolescent marijuana use post-MML were contradicted by replication studies that adjusted for state fixed effects (Harper et al., 2012, Wall et al., 2016). Most previous studies tend to be limited by the inclusion of a small number of states/years, and treat MMLs as uniform across states, rather than a heterogeneous set of provisions; However, research has begun to assess the heterogeneity in state-level MMLs and provisions (Chapman et al., 2016). Moreover, few studies have examined how MMLs affect heavy marijuana use rates among adolescents. This study used 20 years of data collection in 45 states to examine the effects of MMLs, varying provisions and the degree of provision liberalization on adolescent past-30-day marijuana and heavy marijuana use.
Section snippets
Data
Individual-level data (N = 715,014) consisted of state Youth Risk Behavior Surveillance (YRBS) data collected in up to 45 states biennially from 1991 to 2011. The YRBS is a cross-sectional school-based survey of representative samples of 9th through 12th grade students conducted by the Centers for Disease Control and Prevention (CDC) and various state and local agencies. State samples were drawn using a two-stage cluster sampling design that first randomly selected schools to participate, and
Results
The overall prevalence of adolescent past-30-day marijuana use across all study years was 22.7% among adolescents residing in MML states compared to 19.8% in non-MML states (unadjusted OR 1.08, [95% CI = 1.03, 1.13]). Past-30-day heavy marijuana use rates were 7.0% vs. 5.6%, respectively (unadjusted OR 1.12, [95% CI = 1.05, 1.21]). Fig. 1 presents the unadjusted mean values for past-30-day use and heavy use of marijuana in states with and without MMLs from 2001 to 2011. Table 3 presents unadjusted
Discussion
This study utilizing repeated, cross-sectional YRBS data collected from 45 states between 1991 and 2011 found that adolescents living in states with legalized medical marijuana tended to have higher past-30-day marijuana use and heavy marijuana use (≥20 times in past 30 days) rates compared to those living in non-MML states. However, we found no evidence during this study period of an increase in adolescent past-30-day marijuana use or heavy marijuana use after enactment of a MML. Interestingly,
Conflict of interest statement
No conflicts of interest to report.
Contributors
All of the authors contributed to the study conception and design, interpretation of findings, and manuscript preparation and revision. Julie K. Johnson originated the study, conducted the statistical analyses and drafted the manuscript. Sion Harris advised on the conception and design, statistical analysis, interpretation of findings and reviewed drafts of the manuscript. Dominic Hodgkin advised on the statistical analysis, interpretation of findings and reviewed drafts of the manuscript.
Financial disclosure
No financial disclosure to report.
Role of funding source
This research was supported by Grant 5F31DA036923-02 from the National Institute on Drug Abuse (PI: Johnson) and partially supported by Grant T32AA007567 from the National Institute on Alcohol Abuse and Alcoholism (PI: Constance Horgan; Sharon Reif). This article is the sole responsibility of the authors and does not reflect the views of either the National Institute on Drug Abuse or the National Institute on Alcohol Abuse and Alcoholism.
Submission declaration and verification
This manuscript has not been published in any other journal or place, is not under consideration for publication in any other journal, and will not be sent out to any journal while under consideration for publication with Drug and Alcohol Dependence.
Human participant protection statement
This was a secondary analysis of existing, public use, state-level data from 45 states participating in the Youth Risk Behavior Survey (YRBS) and complies with the HIPAA Privacy Rule.
Acknowledgments
The lead author would like to acknowledge: Peter Kreiner, PhD, Rosalie Pacula, PhD for their advisement at varying points during this study.
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