In a new Cato Institute working paper, Harvard economist Jeffrey Miron finds little evidence that the loosening of marijuana prohibition in Colorado has had a noticeable impact on adult or underage cannabis consumption, traffic accidents, violent crime, drug treatment admissions, emergency room visits, drug-related deaths, educational outcomes, or economic growth. Miron, Cato's director of economic studies, considers trends in these indicators before and after 2009, when the medical marijuana industry took off due to regulatory developments that made it more secure, and 2012, when voters approved Amendment 64, which legalized marijuana for recreational use. Generally speaking, there is no significant change in these trends after those policy shifts. Here, for example, is how violent crime rates in Denver look:
In this case, data are available for the months following the beginning of legal recreational sales last January. Looking at murders, aggravated assaults, robberies, and burglaries, Miron concludes that "no measure indicates a significant change in crime after medical marijuana commercialization, legalization adoption, or full legalization implementation."
I have discussed some of these trends here, including crime, underage use, traffic fatalties, and drug treatment admissions. Miron also looks at several educational outcomes: school suspensions, standardized test scores, and high school graduation and dropout rates. Changes in marijuana policy do not seem to have had an impact on these outcomes, with the exception of drug-related suspensions, which rose after the commercialization of medical marijuana in 2009 and again after the legalization of recreational marijuana in 2012, even as total suspensions declined.
Miron not only finds little evidence of negative fallout from changes in Colorado's marijuana policies; he also finds little evidence that legalization has had a positive impact on the measures he considers. It does not seem to have slowed or accelerated economic growth, for example, or to have increased or reduced traffic accidents. Looking at "fatal car crashes, fatalities in car crashes, alcohol-related fatal car crashes, and fatalities in alcohol-related car crashes," Miron finds that "no measure exhibits a substantial change at the time of marijuana policy changes."
Miron concludes that "strong claims about Colorado's legalization, whether by advocates or opponents, are so far devoid of empirical support." As far as broad legalization goes, of course, it is still early going in Colorado, and negative or positive effects may become apparent in the coming years. Miron plans to keep an eye on trends in Colorado and other states that legalize marijuana, ultimately comparing them to data from other states to get a clearer idea of what happens after prohibition ends.