New evidence of the powerful impact of US medical marijuana laws

Medical marijuana laws reduce violent crime in US counties on the Mexican border, according to research by Evelina Gavrilova, Takuma Kamada and Floris Zoutman, which is forthcoming in the Economic Journal.

Their study compares US states that introduce medical marijuana laws with those that do not. They find that when a state on the Mexican border introduces a medical marijuana law, the violent crime rate is reduced by 13% on average.

The reduction in crime is strongest in counties close to Mexico. When inland states introduce medical marijuana laws, this does not have a significant effect on violent crime in inland states. Instead, there are ''spillover'' effects: when inland states introduce medical marijuana laws, this decreases crime in the border region.

Analysing county-level crime data from the Uniform Crime Reports and Supplementary Homicide Records collected by the FBI between 1994 and 2012, the authors also find that:

• Among the US border states, the effect of medical marijuana laws is largest in California (a reduction of 15%) and weakest in Arizona (a reduction of 7%)

• The crimes most strongly affected are robberies (a reduction of 19%) and homicides (a reduction of 10%).

• Homicides that relate to the drug trade reduce by 41%.

The mechanism through which medical marijuana laws affect crime in the border region is likely to be related to Mexican drug trafficking organisations. Medical marijuana laws allow local farmers to cultivate and distribute marijuana, thus replacing illegal marijuana supplied by the drug traffickers.

The loss in revenue results in a decrease in activity by the drug trafficking organisations. This results in a reduction in violence in the border region where the Mexican organisations are most active.

The study provides new insights into methods to reduce violent crime related to drug trafficking. Current efforts have mostly focused on deterrence strategies that aim to reduce the supply of illicit drugs.

The results of this study suggest that violent crime can instead be reduced by introducing legal ways of producing, selling and obtaining drugs within the United States.

Finally as a disclaimer, the study considers the effect of medical marijuana laws on violent crime. Public health and other social consequences of medical marijuana laws have not been considered.

''Is Legal Pot Crippling Mexican Drug Trafficking Organizations? The Effect of Medical Marijuana Laws on US Crime'' by Evelina Gavrilova, Takuma Kamada and Floris Zoutman is forthcoming in the Economic Journal. Evelina Gavrilova and Floris Zoutman are associate professors at the Norwegian School of Economics. Takuma Kamada is a PhD candidate at Pennsylvania State University.

Evelina Gavrilova

Associate Professor at Norwegian School of Economics