Although federal law has forbidden the use and distribution of marijuana in the United States since 1937, states have experimented with marijuana liberalisation policies for the past five decades. State decriminalisation policies were originally enacted in the 1970s, followed by patient medical access laws in the 1990s, and more recently, states have experimented with recreational market legalisation. As a result, there is a wide range of marijuana liberalisation policies across the United States, which is sometimes overlooked or overlooked when evaluating recent legislative developments. Take, for example, the current condition of marijuana policy in the United States at one moment in time. As indicated in Figure 1, as of January 1, 2016, 21 states1 had decriminalised some marijuana possession charges (NCSL 2016a), 26 states had authorised medical marijuana, and 16 states had enacted CBD-only laws (NCSL 2016b) to protect patients.
The tremendous policy variation over time and across states would appear to give researchers ample opportunities to quantitatively assess the effect of marijuana liberalization policies on a variety of health and social outcomes. However, the scientific literature has been slow to develop, and what exists in the literature offers generally mixed and largely insignificant findings. This has led many to conclude that the previous liberalization policies must be harmless and that ongoing legalization would similarly generate very little harm to society. Indeed, recent surveys of people’s attitudes about marijuana show a clear shift in favor of legalization (Caulkins et al. 2015).
A number of factors have driven the policy changes observed over the past several decades, including rising state budgetary costs associated with arresting and incarcerating nonviolent drug offenders (Raphael & Stoll 2013, Reuter et al. 2001), growing scientific evidence of the therapeutic benefits of cannabinoids found in the marijuana plant (Hill 2015, Koppel et al. 2014), and strained state budgets that have caused legislatures to look for new sources of tax revenue (Caulkins et al. 2015, Kilmer et al. 2010).
As we will argue throughout this article, however, at least three reasons suggest that we use caution in drawing conclusions from the mixed empirical evidence or, more importantly, in assuming that a change to legally protected commercial markets would result in outcomes similar to those of the previous experiments. First, the literature has largely treated both decriminalization and medical marijuana policies as if they were simple dichotomous choices, implemented similarly across states. Such a treatment ignores the significant heterogeneity in these policies that can differentially influence harms and benefits and also contributes to what appear to be mixed results from evaluations. Second, the vast majority of policy evaluations conducted thus far examine the effect of the policy in terms of changes in prevalence rates in the general population, which assumes that the proportion of casual and heavy users, who are pooled together in these simple prevalence rates, remains stable even as the policy changes. Finally, research has been slow to consider the extent to which these changes in policies influence the method by which the typical user consumes marijuana. The potential acute harm associated with smoking a joint is different from that associated with consuming an edible or dabbing wax, particularly given that the average potency of the product typically differs and the body’s rate of absorption of THC varies by method (Huestis 2007).
In this article, we review the existing literature on the effects of decriminalization and medical marijuana laws on marijuana use and marijuana use disorders in light of these limitations. Unlike other reviews, our goal is not to summarize all the existing literature on the effects of decriminalization and medicalization. Rather, the purpose of this review is to provide a better understanding of what can be gleaned from the literature when more consideration is given to the complexities of these policies, the populations examined, and the measures of use considered. Doing so allows us to convey the need for more research, in terms of measurement and analysis, before we can truly understand the impacts of marijuana liberalization policies.
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