"Our results are not consistent with the hypothesis that the legalization of medical marijuana caused an increase in the use of marijuana and other substances among high school students. In fact, estimates from our preferred specifications are consistently negative and are never statistically distinguishable from zero."
"There is little evidence that marijuana use is related to the legalization of medical marijuana in either of these data sources [*], a result that is consistent with research showing that marijuana use among adults is more sensitive to changes in policy than marijuana use among youths (Farrelly et al. 1999; Williams 2004)."
[*] data sources are the National Longitudinal Survey of Youth 1997 (NLSY97) and the Treatment Episode Data Set (TEDS)
Anderson, D. Mark; Hansen, Benjamin; and Rees, Daniel I, "Medical Marijuana Laws and Teen Marijuana Use," Social Science Research Network (May 2012), pp. 18-19.