The St. Louis County medical examiner's autopsy of the 18-year-old killed by police in Ferguson, Missouri, found marijuana in his system. With the events leading up to the shooting of Michael Brown still unclear (and with websites like the Drudge Report highlighting the marijuana detail), reports about the autopsy results beg the question of whether marijuana use triggers the kind of violent or belligerent behavior that might lead to a confrontation with police.
The short answer is no.
-- A January study of aggressive behavior published by University of Tennessee and Florida State University researchers concluded marijuana use "did not increase the odds of any type of aggression."
-- Following publication of an April study on marijuana legalization and crime rates, University of Texas criminologist Robert Morris told the Huffington Post much of the evidence "points toward reductions in violent behavior for those who smoke marijuana." The Huffington Post noted "other studies have failed to establish a link between marijuana use and crime."
-- A 2003 National Bureau of Economic Research study by researchers at RAND Corp. and Harvard's Kennedy School of Government noted marijuana "has generally been shown to inhibit aggressive behavior and violence in humans and thus it is believed not to be a major contributor to crime." That study noted while there has been some research suggesting a link between reported cannabis use and crime specifically among juveniles, there is no conclusive evidence the marijuana use causes criminal tendencies.
-- In Colorado, violent crime rates have dropped since marijuana was officially legalized earlier this year.
Despite these studies and others, Obama administration drug czar Gil Kerlikowske last year publicly insisted marijuana is linked to crime. As evidence, Kerlikowske said data proved many people arrested for crimes have marijuana in their systems.
However, the data do not address cause. In fact, the RAND and Harvard researchers concluded such statistics could be explained by the fact marijuana use "may just influence the likelihood of getting caught committing these crimes," rather than actually motivating the crimes themselves.
In reviewing the St. Louis County autopsy on Brown, the Washington Post reported residents and protesters "have noted that allegations of marijuana use have been used in the past by some in an attempt to disparage the character of shooting victims, including in the Trayvon Martin case."