The legalization of medical marijuana has sparked debate across the nation for decades. Some have argued that medical marijuana's legalization will lead to higher crime rates. But according to a new study at UT Dallas, legalization of medical cannabis is not an indicator of increased crime.

It actually may be related to reductions in certain types of crime, said Dr. Robert Morris, associate professor of criminology and lead author of the study published in the journal PLOS ONE.

"We're cautious about saying, 'Medical marijuana laws definitely reduce homicide.' That's not what we're saying," Morris said. "The main finding is that we found no increase in crime rates resulting from medical marijuana legalization. In fact, we found some evidence of decreasing rates of some types of violent crime, namely homicide and assault."

The UT Dallas team began its work in summer 2012 after repeatedly hearing claims that medical marijuana legalization posed a danger to public health in terms of exposure to violent crime and property crime.

The study tracked crime rates across all 50 states between 1990 and 2006, when 11 states legalized marijuana for medical use: Alaska, California, Colorado, Hawaii, Maine, Montana, Nevada, Oregon, Rhode Island, Vermont and Washington. Since the time period the study covered, 20 states and Washington, D.C., have legalized marijuana for medical use.

Using crime data from the FBI's Uniform Crime Report, the researchers studied rates for homicide, rape, robbery, assault, burglary, larceny and auto theft, teasing out an effect for the passing of medical marijuana laws.

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None of the seven crime types increased with the legalization of medical marijuana.

Robbery and burglary rates were unaffected by medical marijuana legalization, according to the study. These findings run counter to the claim that marijuana dispensaries and grow houses lead to an increase in victimization because of the opportunities for crime linked to the amount of drugs and cash that are present.

Morris said the models accounted for an exhaustive list of sociodemographic and econometric variables that are well-established links to changes in crime rates, including statistics on poverty, unemployment, college education, prison inmates and even the amount of beer consumed per person per year. Data came from the U.S. Census Bureau, the Bureau of Economic Analysis and the Bureau of Labor Statistics.

"The results are remarkable," Morris said. "It's pretty telling. It will be interesting to see what future studies hold."

Once data are available, the researchers plan to investigate the relationship between recreational marijuana legalization and crime in Washington and Colorado, where the legalized marijuana marketplace is taking shape.

While it's too soon to say if there are definitive drawbacks to legalizing marijuana for medical purposes, Morris said, the study shows that legalization does not pose a serious crime problem, at least at the state level.

"This new information, along with continued education of the public on the realities of the negative aspects of smoking marijuana -- which there are considerable negative attributes -- will make the dialogue between those opposed and in favor of legalization on more of an even playing field," Morris said. "It takes away the subjective comments about the link between marijuana laws and crime so the dialogue can be more in tune with reality."

UT Dallas doctoral student Michael TenEyck, assistant professor Dr. J.C. Barnes and associate professor Dr. Tomislav V. Kovandzic, all from the criminology program, also contributed to the study as co-authors.