The goal of this paper is to estimate the impact of state laws that permit medical use of marijuana on other risky health behaviors, such as smoking, binge drinking, and use of other illicit drugs. Marijuana is the most commonly used drug in the U.S. and emergency room visits and substance abuse treatment related to marijuana use has increased over time. Although marijuana is a Schedule I drug under the Controlled Substance Act of 1970, many states in recent decades have legalized marijuana use for certain medical conditions.  As more states allow medical use of marijuana, risk perceptions of using marijuana and possibly other drugs may decrease. It may also reduce the costs involved in getting marijuana (since MML protects patients to use marijuana for medical purposes). 

There are several mechanisms by which legalized medical marijuana use might affect other risky health behaviors.  Marijuana could act as a “gateway drug”, leading to subsequent consumption of hard drugs such as heroin or cocaine (e.g. Mills and Noyes, 1984; Newcomb and Bentler, 1986; Deza, 2012).  Furthermore, marijuana may be a complement to, or substitute for, other substances (e.g. Pacula, 1998; Farrelly et al., 1999, 2001; Williams et al., 2004; Chaloupka et al., 1999; Dinardo and Lemiuex, 2001; Yoruk and Yoruk, 2011).  Recent studies have examined the impact of medical marijuana policies on youth marijuana consumption and tend to find a positive association (Cerda et al., 2012; Wall et al., 2011; Lynne-Landsman et al., 2013). A contribution of my study is that it examines the adult population.

In this paper, I examine the data from the restricted-use National Survey of Drug Use and Health (NSDUH), which is a repeated cross sectional dataset that spans 2004 to 2011.  It collects information from roughly 70,000 randomly selected individuals in the US of age 12 or older.  From 2004-11, 8 states have allowed marijuana use for medical purpose.  Exploiting this variation across states over time, I estimate difference-in-differences models to examine the impacts of these policy changes on risky health behaviors.  I also estimate regressions by relevant subgroups such as adolescents, adults with chronic medical conditions, and by race, education, and gender. I examine outcomes on medical and non-medical marijuana use, drinking, smoking, driving under the influence of drugs or alcohol, other drug use, marijuana abuse, and non-drug related outcomes such as suicide and number of arrests in the past year.  

I find positive and significant relationships between MML and 1) medical marijuana use and 2) smoking in the past month.  For alcohol, I find a negative and significant relationship between MML and drinking alcohol in the past month.  This supports previous research that alcohol and marijuana are substitutes. This study provides early estimates of the impact of recent medical marijuana laws on risky health behaviors.  This is useful for both understanding the possible unintended consequences of such laws and for better understanding the determinants of risky health behaviors.