Marijuana liberalization policies: why we can't learn much from policy still in motion [Point/Counterpoint] (2014)

California legalized the use of marijuana for medicinal purposes nearly 17 years ago, representing a major challenge to the federal government’s scheduling of marijuana as a Schedule I drug in the 1970 Controlled Substance Act. As many predicted, California was simply the first. As of May 2013, 19 states and the District of Columbia now provide legal protection to patients, and in many cases caregivers, for possession and supply of marijuana for medicinal purposes. In November 2012, Colorado and Washington went even further, legalizing the sale and possession of marijuana for recreational purposes. Given the tremendous natural experiment that is taking place, one might expect that much would already be known about the benefits and harms of liberalizing marijuana policies. Unfortunately, however, the tremendous uncertainty regarding what protections actually exist, and for whom, in addition to the enormous heterogeneity in the medical marijuana laws (MMLs) that continue to change over time, has meant that we do not yet know as much as we should.
The questions of whether marijuana is medicine and whether recreational marijuana use is harmless are necessarily intertwined in all of the debates over policy reform, but these are not the focus of this discussion. There is legitimate evidence that active cannabinoids available in the marijuana plant are useful in the treatment of some medical conditions and symptoms (Institute of Medicine, 1999; Leung, 2011; Watson, Benson, & Joy, 2000) and have been for centuries (Eddy, 2010; Grinspoon, 2005). As such, it is not surprising that the American Medical Association (AMA) adopted a resolution in 2009 urging the federal government to review the case for rescheduling marijuana, noting that doing so would facilitate research and development of cannabinoid-based medicine and avoid the patchwork of inadequate state laws that do not focus on establishing clinical guidelines or standards for medically prescribing marijuana (AMA, 2009). There is also evidence in the biomedical and public health literatures of reasonable pathways through which marijuana can harm health or affect health outcomes (see Hall & Degenhardt, 2009; Hall & Pacula, 2003; Room et al., 2010; or Caulkins et al., 2012 for extensive reviews). However, the causal linkage between recreational marijuana use and many of these health outcomes has yet to be fully established and continues to be a matter of scientific inquiry due to imprecise information on amounts consumed or potency of the substance used. Nonetheless, state liberalization policies move forward, and scientists are trying to use these natural experiments to assist in the identification of benefits and harms from these policies. [Extract]