This study highlights the key role that macro-level factors, such as policy changes and community norms about substance use, play in shaping marijuana use and abuse/dependence. Future studies are also needed on the consequences of increased marijuana use, such as accidents, aggression, school drop out, psychosis, HIV and sexually transmitted disease rates (Fergusson et al., 2003a; Fergusson et al., 2003b; Hall and Degenhardt, 2009) as well as on the particular impact of medical marijuana legalization on youth, who bear a disproportionate burden of marijuana-related disorders (Budney and Moore, 2002), and are vulnerable to the advertising effects of other substances such as tobacco (Hanewinkel et al., 2011). In particular, future studies in the United States and elsewhere can build on our findings by comparing trends in community norms, marijuana use and abuse/dependence before and after the legalization of marijuana, to understand the relative contribution of medical marijuana legalization and community norms on changes in marijuana use and abuse/dependence.
