High Times: The Effect of Medical Marijuana Laws on Student Time Use

Marijuana use is strongly correlated with low educational attainment such as school dropout and truancy. Medical literature suggests that marijuana use could change motivation and cognitive abilities and therefore it could harm educational outcomes. However, empirical evidence on the causal link between marijuana use and educational outcomes is rather limited due to lack of exogenous variation. In fact, there is only a small number of studies, and it is unclear to what extent their findings are driven by unobserved heterogeneity.

Twenty-three states and the District of Columbia have passed medical marijuana laws. Several existing studies have shown that these laws increase marijuana use among adults. In this paper, we estimate the effects of medical marijuana laws on student time use based on American Time Use Survey. We apply a difference-in-difference research design and estimate a flexible fixed effects model that controls for state fixed effects and their specific time trends, year fixed effects, month fixed effects, days of week fixed effects, and students demographics.  

We find that medical marijuana laws decrease homework and in-class time but increase television time among part-time college students. Out estimates suggest that on an average day, after the passage of medical marijuana laws, part-time college students spend 42 minutes less on doing homework, 37 minutes less on attending class, but 60 minutes more on watching television. When time is measured in terms of a proportion of non-sleep time, these effects are estimated to be around 4–5% of non-sleep time. In addition, we find that the increase in television time is driven by the intensive margin, while changes at the extensive margin play an important role in the decreases in homework and in-class time.

Consistent with the existing finding that these medical marijuana laws do not affect juvenile drug use, there is no effect among high school students. However, we do not find similar effects on time sue among full-time college students either. Interestingly, the effects appear to be somewhat heterogeneous and stronger among disadvantaged students. Among part-time college students, the estimated effects among Blacks students are more than twice greater than among White students. Overall, our findings suggest that marijuana use may causally harm educational outcomes among relatively disadvantaged students.