Previous work has shown that medical marijuana markets have spill-over effects on recreational markets, increasing adult prevalence rates. It remains unclear, however, whether the increase in use reflects a rise in uptake or a decrease in quitting. To shed light on this issue, we study the impact of medical marijuana markets on the decision to quit. People quit using marijuana when the costs of continuing use outweigh the benefits, which prior literature had consistently demonstrated occurs around the ages of 27 to 30, when more adult responsibilities set in (Hall and Pacula, 2003; Terry et al., 2017). If state medical marijuana policies provide legal protections that spill over to recreational users or reduce the cost of using by lowering the search costs and monetary price (Anderson et al., 2013), then such policies could lead to lower quit rates and hence longer durations of use. This impact on quitting behavior is important to consider for at least two reasons. First, most of the identified health and social impacts associated with marijuana use are attributed to long term use, including dependence, cardiovascular risk, and respiratory problems (Hall 2015), anxiety and depression (Van Ours and Williams, 2011, 2012; Anderson et al., 2013); and poor schooling outcomes (Van our and Williams, 2009; McCaffrey et al., 2010; Marie and Zolitz, 2017}. Second, evidence from the tobacco literature clearly demonstrates that tobacco control policies influence smoking initiation and cessation differentially. As a result, estimates of policy impacts on static measures of demand at a point-in-time confound heterogeneous responses across those who are making decisions about initiating and those who are deciding whether to quit.
Using individual-level longitudinal information on marijuana use in the NLSY97, we exploit geographic and temporal variation in the presence and legal protection of marijuana dispensaries impact quitting behavior. Our results reveal no evidence of any impact when the sample is pooled and assumed to be homogenous in their responsiveness to these policies. Allowing for heterogenous effects across gender and race/ethnicity reveals important differences, however. White males delay quitting in response to the presence of operating retail dispensaries, while black males respond to the legal protection of retail dispensaries, and Hispanic males delay quitting in response to both the legal protection and presence of operating retail medical marijuana dispensaries. Females are not sensitive to either the presence or protection of retail medical marijuana dispensaries. We conclude that the decision to quit using marijuana among men, and therefore the duration of use, is sensitive to the operation of marijuana markets, but it is the legal protection of these markets that influence duration for minorities, possibly because of the differential enforcement of marijuana laws against minorities.
