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Violent Crime Drops Where People Have Access to Marijuana, Study Suggests

Two scientific papers suggest the dire warnings we've heard about marijuana for decades don't hold water.

Opponents of marijuana legalization, particularly members of law enforcement, frequently claim that liberalizing cannabis laws will lead to an increase in incidences of criminal activity, such as burglary, robbery, and driving under the influence. But two recent scientific papers report that just the opposite is true.

In the most recent paper, published online in March in the scientific journal PLoS ONE, researchers at the University of Texas at Dallas reported that the enactment of laws legalizing people’s access to medical marijuana is not associated with any rise in statewide criminal activity, and that it may even be related to reductions in incidences of violent crime.

Investigators tracked crime rates across all 50 states in the years between 1990 and 2006, during which time 11 states—Alaska (1998), California (1996), Colorado (2000), Hawaii (2000), Maine (1999), Montana (2004), Nevada (2000), Oregon (1998), Rhode Island (2006), Vermont (2004), and Washington (1998)—legalized the use, home cultivation, and (in some cases) the retail dispensing of marijuana for medical purposes. (A total of 20 states and the District of Columbia have now approved similar laws.) Authors reviewed FBI Uniform Crime Report data to determine whether there exists any association between the enactment of medicinal cannabis laws and rates of statewide criminal activity, specifically the number of reported crimes involving homicide, rape, robbery, assault, burglary, larceny, and auto theft. Their analysis is the first to look at multiple offenses across multiple states and time periods to determine whether medical marijuana legalization impacts state crime rates.

Authors reported that the passage of medical marijuana laws is not associated with an increase in any of the seven crime types assessed, but that liberalized laws are associated with decreases in certain types of violent crime. Authors wrote:

“The central finding gleaned from the present study was that MML (medical marijuana legalization) is not predictive of higher crime rates and may be related to reductions in rates of homicide and assault. Interestingly, robbery and burglary rates were unaffected by medicinal marijuana legislation, which runs counter to the claim that dispensaries and grow houses lead to an increase in victimization due to the opportunity structures linked to the amount of drugs and cash that are present.”

They concluded:

“In sum, these findings run counter to arguments suggesting the legalization of marijuana for medical purposes poses a danger to public health in terms of exposure to violent crime and property crimes. To be sure, medical marijuana laws were notfound to have a crime exacerbating effect on any of the seven crime types. On the contrary, our findings indicated that MML (medical marijuana legalization) precedes a reduction in homicide and assault. While it is important to remain cautious when interpreting these findings as evidence that MML reduces crime, these results do fall in line with recent evidence and they conform to the longstanding notion that marijuana legalization may lead to a reduction in alcohol use due to individuals substituting marijuana for alcohol. Given the relationship between alcohol and violent crime, it may turn out that substituting marijuana for alcohol leads to minor reductions in violent crimes that can be detected at the state level.”

Commenting on the findings in an accompanying news release, the study’s lead author, Robert Morris, associate professor of criminology, said, "The results are remarkable.… It takes away the subjective comments about the link between marijuana laws and crime so the dialogue can be more in tune with reality."

The paper’s results, specifically the notion that cannabis liberalization may lead to a reduction in alcohol-induced criminal activity, are similar to those previously documented in a study published last year in the Journal of Law and Economics. In that study, researchers at Montana State University, the University of Oregon, and the University of Colorado assessed whether the enactment of medical cannabis laws was associated with a reduction in incidences of alcohol-related traffic fatalities for the years 1990 to 2010. It was.

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