A few weeks ago, in a column about the impact of marijuana legalization, I noted that there is not much evidence to support the frequently voiced fear that allowing medical use encourages teenagers to smoke pot. A new study by three economists reinforces that point, finding that the adoption of medical marijuana laws is not associated with increases in cannabis consumption by high school students. "Our results are not consistent with the hypothesis that legalization leads to increased use of marijuana by teenagers," write D. Mark Anderson of Montana State University, Benjamin Hansen of the University of Oregon, and Daniel Rees of the University Colorado in a working paper published by the National Bureau of Economic Research.
Anderson et al. used data from three sources: the National Youth Risk Behavior Survey, the National Longitudinal Survey of Youth, and the Treatment Episode Data Set. "These analyses provide further evidence that youth marijuana consumption does not increase with the legalization of medical marijuana," they write. "Our results are not consistent with the hypothesis that the legalization of medical marijuana caused an increase in the use of marijuana among high school students. In fact, estimates from our preferred specification are small, consistently negative, and are never statistically distinguishable from zero."
The impact of general legalization, of course, might be different. Assuming that legal marijuana businesses in places such as Colorado and Washington eventually displace the black market, teenagers will find it harder to buy pot directly, since licensed sellers, unlike your average street dealer, check IDs to make sure buyers are at least 21. But it may become easier for teenagers to obtain pot indirectly, via legal buyers. Still, Anderson et al.'s findings are significant, because in some states (including Colorado, Washington, and California) the rules for obtaining medical marijuana are loose enough that it's easy for recreational consumers to pose as patients. In fact, critics commonly complain that medical marijuana in those states is legalization by another name. Rees nevertheless told The Washington Post that the overall results of this study hold true for individual states as well. "No single state stood out," he said. "The effect of passing a medical marijuana law on youth consumption appears to be zero across the board."