Legalizing medical marijuana causes no increase in crime, according to a new study. In fact, legalized medical pot may reduce some violent crime, including homicide, University of Texas at Dallas researchers wrote in a journal article published this week.
The study, published in PLOS ONE on Wednesday, appears to settle concerns, simmering since the first states approved medical marijuana nearly two decades ago, that legalization would lead to more crime.
"We believe that medical marijuana legalization poses no threat of increased violent crime," Robert Morris, the study's lead author, told The Huffington Post.
Morris, associate professor of criminology at UT Dallas, and his colleagues looked at crime rates for all 50 U.S. states from 1990 to 2006. During this period, 11 states legalized medical marijuana. The researchers examined legalization's effect on what the FBI calls Part I crimes, which include homicide, rape, robbery, aggravated assault, burglary, larceny and auto theft.
"After controlling for a host of known factors related to changes in crime rates -- we accounted for factors such as poverty, employment, education, even per capita beer sales, among other things -- we found no evidence of increases in any of these crimes for states after legalizing marijuana for medical use," Morris said. "In fact, for some forms of violence -- homicide and assault -- we found partial support for declines after the passing of this legislation."
Data for the study came from state websites, FBI Uniform Crime Reports, the census, The Bureau of Labor Statistics, The Bureau of Economic Analysis and the Beer Institute.
The study did not explore a relationship between marijuana use and violent crime, Morris said. Rather, the research team looked at legalization's effect on crime. Other studies have failed to establish a link between marijuana use and crime.
"The findings on the relationship between violence and marijuana use are mixed and much of the evidence points toward reductions in violent behavior for those who smoke marijuana," Morris said. "In fact, researchers have suggested that any increase in criminality resulting from marijuana use may be explained by its illegality, rather than from the substance itself."
Other research suggests alcohol is a much more significant factor than marijuana when it comes to violent crime. A report from the National Institute on Alcohol Abuse and Alcoholism found that 25 percent to 30 percent of violent crimes are linked to alcohol use. A separate study in the journal of Addictive Behaviors noted that "alcohol is clearly the drug with the most evidence to support a direct intoxication-violence relationship," and that "cannabis reduces likelihood of violence during intoxication." The National Academy of Sciences found that in chronic marijuana users, THC -- the active ingredient in pot -- actually causes a decrease in "aggressive and violent behavior."
Laws in 20 states and the District of Columbia allow marijuana for medical use. Colorado and Washington state have legalized marijuana for recreational use. About a dozen other states are likely to legalize marijuana in some form in the coming years.
Michael Elliott, executive director of the Marijuana Industry Group, said he was pleased, but not surprised, by the new research.
"As a trade association, we have supported the development of this comprehensive regulatory framework, including transparency, accountability, licensing, background checks, financial disclosures, seed to sale tracking, and consumer safety protections like packaging, labeling, and testing," Elliott said. "While this program is cumbersome for the small business owners in this industry, it is far better than choosing black market operators who use violence to dominate the sale of marijuana and prey on our children.”