State medical marijuana laws can be seen as one indicator of group-level approval of marijuana use. These laws legalize marijuana use, when authorized by a physician, for medical purposes such as alleviation of nausea and vomiting from chemotherapy, wasting in AIDS patients, and chronic pain unresponsive to opioids (Procon.org). Between 1996 and 2011, 16 states passed laws legalizing marijuana use for medical purposes. Medical marijuana laws can be used to represent state-level norms on marijuana use because generally, a substantial relationship exists between public opinion and policy decisions (Brooks, 2006; Burstein, 2003, 2006; Nielsen, 2010) and specifically, because community norms regarding substance use (e.g., drinking and cigarette smoking) are directly related to policy and enforcement efforts (Lipperman-Kreda and Grube, 2009; Lipperman-Kreda et al., 2010). For example, Khatapoush et al. found that among individuals aged 16-25 in California, marijuana use did not increase in 1996 after legalization of medical marijuana, but marijuana use was higher in California than in other 10 comparison states in 1995, 1997 and 1999 (Khatapoush and Hallfors, 2004). This suggests that state-level norms may have contributed to both the legalization of medical marijuana and to higher rates of use in California in comparison to other states.
