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Does Legal Cannabis Affect Crime? Not in Washington and Colorado, Study Finds

By Leo Bear-McGuinness

Published: Oct 08, 2019   
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One of the great arguments for legalizing cannabis – that it would reduce crime rates – has been challenged by a new statistical study, which found that there hasn’t been any significant change in violent or property crime rates in Colorado and Washington since each legalized recreational marijuana.

However, the findings may be specific the western and north-western states, as another study published in the Economic Journal in 2017 found that states on the US-Mexico border that legalized medical marijuana saw a decrease in violent crimes from 12.5 to 5.6 percent.

Green streets

Published in Justice Quarterly, and funded by a grant from the National Institute of Justice, the new study compared monthly crime rates in Colorado and Washington to crime rates in 21 states that haven't legalized cannabis for recreational or broad medical purposes.

“We were able to get the crime rates data from FBI uniform crime report – from 1999 to 2016, which was the most recent data that we had at the time of the study,” Ruibin Lu, an assistant professor of criminal justice at Stockton University and the study’s first author, told Analytical Cannabis.

“We were focusing on the FBI part one crimes, so, homicide, sexual assault, robbery, aggravated assault, burglary, larceny, and all of that. We see [sic] what was the change after the legalization and after the retail sales, and we compare those change in Washington, Colorado to the states that did not legalize marijuana.”

Other crime researchers have suggested that cannabis legalization could increase violent crime rates if it boosted youth delinquency and provided burglars with vulnerable businesses. But despite a brief increase in larceny in Washington immediately following legalization, Lu and her co-authors found that recreational cannabis sales had minimal to no effect on major crimes in both states.

“Property crime rates increased temporarily after the legalization, and aggravated assaults also temporarily increased in Washington,” Lu said. “And if we look at a long term, the changes [that] occurred in Washington [and] Colorado are not significantly different from the changes [that] occurred in other parts of the country.”

Marijuana and motive

The researchers do note that the study has its limitations. For example, marijuana’s effect on non-invasive crimes wasn’t investigated – a separate study has linked Colorado’s legalization to an increase in car accidents – and the crime rates of certain communities wasn’t taken into consideration. But Lu is keen to address these oversights in further studies.

“There could be a change of crime rates in particular community, like a county or city. And that is going to be the next step of our research,” she added.

“We would also like to see the impact of marijuana on more type of crimes… such as driving under the influence of marijuana. So, we would like to study that and see if any specific crime that is not in this paper could be affected by legalization.”

As for the crime of underage cannabis use, other recent research has indicated that localized cannabis legalization could actually be reducing the number of teenage consumers. One study found that states which legalized recreational cannabis were associated with an 8 percent fall in the number of high school-age teenagers who claimed they used cannabis in the last 30 days.

“I think the big takeaway is that we find no evidence that teen marijuana use goes up after legalization for medicinal or recreational purposes,” Mark Anderson, an associate professor at Montana State University and lead author of that study, told Analytical Cannabis in July

Leo Bear-McGuinness

Science Writer & Editor

Leo joined Analytical Cannabis in 2019. From research to regulations and analysis to agriculture, his writing covers all the need-to-know news for the cannabis industry. He holds a Bachelor's in Biology from Newcastle University and a Master's in Science Communication from the University of Edinburgh.


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