A reexamination of medical marijuana policies in relation to suicide risk
Introduction
Over the past two decades, 23 states and the District of Columbia have legalized marijuana for medical use in the U.S. (Anderson et al., 2014, Pacula et al., 2013). These policies were adopted at different times, allowing researchers to analyze the effects of policy changes as a natural experiment: differences in medical marijuana policies between states over time allow investigators to draw inferences about whether policy that could facilitate access to marijuana are causally associated with key public health outcomes (Anderson et al., 2013, Anderson et al., 2014, Cerdá et al., 2012, Choo et al., 2014, Gorman and Charles Huber, 2007, Harper et al., 2012, Lynne-Landsman et al., 2013, Pacula et al., 2013, Rylander et al., 2014, Schuermeyer et al., 2014, Wall et al., 2011). In one of the more intriguing examples of such a study, Anderson and colleagues examined the association between legalization of medical marijuana and changes in state suicide rates over the period 1990–2007 (Anderson et al., 2014). Their results suggested that legalization of medical marijuana led to a decrease in suicide rates. Specifically, they reported that legalization was associated with a 5% decrease in the suicide rate for men overall, about a 10% decrease in the suicide rate of men aged 20 through 29, and a nearly 14% decrease in men aged 30 through 39.
If the legalization of marijuana for medical purposes truly leads to reductions in suicide rates, this would have important implications for public health and policy. Suicide is among the ten leading causes of death in the United States and the 4th leading contributor to years of potential life lost among people under 65 (Centers for Disease Control and Prevention, 2014, Murphy et al., 2013). Any true effect on suicide rates should be seriously considered in the policy debates surrounding both medical and recreational marijuana. However, a protective effect against suicide is surprising given that neurodevelopmental and psychiatric effects—including suicide risk—are among the primary health concerns associated with regular marijuana use (Batalla et al., 2013, Hall and Degenhardt, 2009, Meier et al., 2012, Moore et al., 2007, Price et al., 2009, Van Ours et al., 2013, Volkow et al., 2014). Given the relevance of such a finding to policy, the suggestion that medical marijuana policies might lead to lower rates of suicide warrants closer scrutiny.
In the present study, we sought to extend the work exploring the association between medical marijuana policy and reduced suicide risk (Anderson et al., 2014). We utilized data from individual death records, which allowed us to adjust for demographic variables at an individual level. This was not possible in the prior study, which analyzed state suicide rates instead of individual death records. Yet adjusting for demographic variables could be important because they may be associated with suicide rates, and, as key characteristics of state electorates, could influence state policy change. For example, race and educational attainment, which were not addressed in the prior study, are well known to be associated with suicide rates (Centers for Disease Control and Prevention (CDC), 2013, Crosby et al., 2013, Crosby et al., 2011). We also adjusted for several additional state policies and characteristics that past research suggests could be relevant. For example, we have recently shown that state tobacco control policies may influence suicide risk (Grucza et al., 2014). Tobacco control policies also likely influence the prevalence of marijuana use (Chaloupka et al., 1999, Farrelly et al., 2001, Williams et al., 2004), and may influence alcohol use which could be an important determinant of suicide risk (Kaplan et al., 2014, Krauss et al., 2014, Young-Wolff et al., 2013a, Young-Wolff et al., 2013b). We also included measures of state political orientation, per-capita mental health spending, and health insurance coverage, all of which may be associated with suicide risk (Kposowa, 2013, Tondo et al., 2006, Yoon and Bruckner, 2009) and are plausibly related to state policy environments. If these factors changed concurrently with adoption of medical marijuana policy, lack of explicit control for them could lead to biased estimates of the association between medical marijuana policy and suicide. Finally, we incorporated more recent data into our analyses, reflecting newly adopted state medical marijuana policies.
Section snippets
Overview
As an initial step, we conducted analyses comparable to those used in the prior report on medical marijuana policy and suicide, employing data from the same time period and including the same set of covariates (Anderson et al., 2014). However, our analyses utilized individual-level data modeled via logistic regression, whereas the previous report described the association between log-transformed state-level suicides rates modeled from aggregated data using linear regression. Because of these
Results
Initial analyses examined the association between medical marijuana policies and suicide risk over the period 1990–2007 to allow for comparison with results obtained by Anderson et al. (2014). Model development is described in Table S1 (see Supplemental Material); results are shown in Tables S2 and S3 (see Supplemental Material). Similar to the prior results, medical marijuana policies exhibited a significant protective association among men overall, and among the 20–29 and 30–39 year age
Discussion
In this report, we show that the association between state medical marijuana policy and suicide risk was not statistically significant, nor even suggestive of a protective effect, after adjustment for key covariates. Though an earlier report demonstrated an apparent correspondence between the legalization of medical marijuana and a decrease in suicide rates among men (Anderson et al., 2014), incorporation of demographic variables and additional state characteristics into the regression models
Role of the funding source
The authors are responsible for the content; the NIH played no role in the development of this content aside from funding.
Contributors
Richard A. Grucza conceived and designed the study, conducted analyses, and led writing of the manuscript. Michael Hur and Melissa J. Krauss conducted analyses and critically reviewed the manuscript. Arpana Agrawal and Andrew D. Plunk drafted portions of the manuscript and critically reviewed it. Patricia A. Cavazos-Rehg critically reviewed the manuscript. Frank J. Chaloupka advised on analyses and critically reviewed the manuscript. Laura J. Bierut advised on the interpretation of the data and
Conflicts of interest
L.J.B. is listed as an inventor on Issued U.S. Patent 8,080,371,“Markers for Addiction” covering the use of certain genetic polymorphisms in determining the diagnosis, prognosis, and treatment of addiction.
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