The legalization of recreational marijuana: how likely is the worst-case scenario?

Last fall, voters in Colorado and Washington approved measures legalizing the recreational use of marijuana. In the near future, residents of these states who are 21 years of age and older will be able to purchase marijuana at retail stores (Donlan, 2013). Although it can be challenging to predict future behavior, Mark Kleiman, a prominent drug policy expert, described what might be characterized as the worstcase scenario. According to Kleiman, this scenario would involve three elements: more heavy drinking, “carnage on our highways,” and a “massive” increase in the use of marijuana by minors (Livingston, 2013). Below, we discuss the likely effects of legalizing marijuana for recreational use on alcohol consumption, traffic fatalities, substance use among high school students, and other outcomes of interest to policymakers and the public. Our discussion draws heavily on studies that have examined the legalization of medical marijuana. These studies are relevant because, in states such as California, Colorado, Oregon, and Washington, the legalization of marijuana for medicinal purposes approaches de facto legalization of marijuana for recreational purposes. One of the key unknowns in the debate over legalization concerns the relationship between alcohol and marijuana use. Researchers have attempted to produce causal estimates of this relationship by exploiting cross-sectional policy and price variation (Pacula, 1998; Williams et al., 2004). We note that these estimates could easily be spurious and that more reliable estimates based on clearly defined natural experiments show that alcohol and marijuana are substitutes. Because the social costs associated with the consumption of alcohol clearly outweigh those associated with the consumption of marijuana, we conclude that legalizing the recreational use of marijuana is likely to improve public health, although plenty of unanswered questions remain.