Ten U.S. states and the District of Columbia allow the sale, possession, and use of cannabis for recreational purposes, and 33 states and the District of Columbia allow medical cannabis.

Lorine A. Hughes, associate professor in the School of Public Affairs at the University of Colorado Denver, who led the study, said: “We found that neighborhoods with one or more medical or recreational dispensary saw increased crime rates that were between 26 and 1,452% higher than in neighborhoods without any commercial marijuana activity. But we also found that the strongest associations between dispensaries and crime weakened significantly over time.”

The researchers looked at both medical and recreational dispensaries from 2012 to 2015 (Colorado legalized cannabis in 2014). They examined the extent to which dispensaries were associated with neighborhood crime and disorder independently of other characteristics of the neighborhoods, such as a concentration of high-risk commercial establishments such as check-cashing stores.

Measures of crime and disorder were drawn from the Denver Police Department and included aggravated assault, auto theft, burglary, drug and alcohol offenses, murder, public disorder, robbery, and theft from a car.

The authors caution that the results of the study, based only on information from Denver immediately after legalization and before market saturation, may not be generalizable to other geographic areas. They also note that because the study relied on official police data to measure crime and disorder, it's possible that police targeted neighborhoods with marijuana dispensaries, which would over-estimate the association between these facilities and crime and disorder.

"Our findings have important implications for the marijuana industry in Denver and the liberalization of marijuana laws nationwide," suggests Lonnie M. Schaible, associate professor in the School of Public Affairs at the University of Colorado Denver, who coauthored the study. "Although our results indicate that both medical and recreational marijuana dispensaries are associated with increases in most major crime types, the weak strength typical of these relationships suggests that, if Denver's experience is representative, major spikes in crime are unlikely to occur in other places following legalization."

The authors suggest that, rather than fighting to oppose legalized marijuana, which has become a multi-billion dollar industry and is expected to create more than a quarter of a million jobs by 2020, it may be more expedient to develop and support secure and legal ways for dispensaries to engage in financial transactions.