Legalizing Medical Marijuana Not Linked to Rise in Violent Crime

As marijuana laws become more relaxed in the US and more states legalize marijuana for medicinal use, crime rates do not increase, according to a new study in the journal PLOS One. 

Opponents of marijuana legalization in the US have cited the threat in increasing crime rates as a reason to keep the drug illegal, but lead study author Robert Morris, an associate professor of criminology at University of Texas at Dallas, said the legalization of medicinal cannabis is not correlated with increased crime.

In fact, Morris says, marijuana legalization may be associated with a reduction of certain types of crime.

"We're cautious about saying, 'Medical marijuana laws definitely reduce homicide.' That's not what we're saying," Morris said in a statement. "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."

Morris and his colleagues began their research in 2012 after repeatedly hearing claims that medical marijuana legalization posed threats to public health in the form of violent crime and property crime.

To see if these claims were justified, the researchers tracked crime rates across all 50 states between 1990 and 2006. In that period, 11 states legalized marijuana for medical use. After 2006, an additional four states legalized medicinal marijuana. Currently 20 states and the District of Colombia have made medical marijuana legal.

The researchers analyzed rates of homicide, rape, robbery, assault, burglary, larceny and auto theft in every state between 1990 and 2006, finding no increase in any of the seven crime times after the legalization of marijuana.

Overall, robbery and burglary rates were not affected by marijuana legalization, a find the study authors run contrary to what many opponents to marijuana legalization believe.

Even factoring for socioeconomic and demographic variables have have been established as links to fluctuations in crime rate, poverty, education, unemployment and incarceration, the researchers still did not find any link to a rise in crime upon the legalization of medical marijuana.

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

In the future, the researchers plan to study the effects on crime related to the legalization of recreational marijuana use in Washington state and Colorado.

Morris said that it's too soon to say whether there are any definite drawbacks to legalizing medical marijuana, but the study does now a link to a related increase in violent crime.