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Grand jury testimony suggested marijuana made Michael Brown violent. That's unlikely.

A picture of Michael Brown is held up at a protest.
A picture of Michael Brown is held up at a protest.
Joe Raedle / Getty Images News

Michael Brown had marijuana in his system when Darren Wilson shot and killed him on August 9, according to the official and independent autopsies.

In the grand jury testimony released to the public Monday, both prosecutors and grand jurors seemed to push the idea that highly concentrated pot made Brown more likely to be aggressive — even when an unnamed medical expert insisted that it's unlikely pot could make Brown attack Wilson.

"The amount of marijuana he has could cause abnormal behavior, but usually doesn't," the unnamed expert said on November 13. "Ninety-nine out of 100 people taking marijuana aren't going to get in a fight with a police officer over it in my experience."

Immediately after, a prosecutor questioned the expert's credentials: "Can I just clarify something here, doctor? Your credentials are as a forensic pathologist, although you have a working understanding of toxicology, you are not a toxicologist, correct?" A grand juror joined in, suggesting the expert had no way of confirming that his statements are true.

But there's actually no reason to believe, based on the available research and the scientific understanding of pot, that marijuana would actually make someone more violent.

The use of Brown's toxicology report to suggest that he was somehow violent at the time of his death is something we've seen before. When Trayvon Martin's toxicology report indicated he had marijuana in his system, detractors used the information to suggest the late teen, who was unarmed when he was shot and killed in 2012 by George Zimmerman, was a lawbreaker and aggressive at the time of his death. But marijuana has never been definitively linked to more aggression or violence.

While some research suggests marijuana users are more likely to be aggressive, multiple studies have found the connection between marijuana use and aggression fades away when controlling for other variables such as alcohol and hard drug use. Marijuana use, in other words, doesn't appear to lead to more violence, and higher pot use doesn't even correlate with more violence if other factors are taken into account.

A recent study on the topic, from researchers at the University of Tennessee in Knoxville, found that there's no connection between domestic abuse and marijuana. The Knoxville researchers acknowledged that the issue needs more study, especially given the conflicting findings in previous studies. But the study shows that a link between pot and aggression is, at the very least, nowhere close to established.

Similarly, another recent study from researchers at the University of Buffalo found marijuana users are actually less likely to report domestic violence — even after controlling for factors like demographic variables, behavioral problems, and alcohol use. That doesn't prove a causal link between marijuana use and reduced violence, but it certainly goes against the notion that marijuana would make someone more violent.

This makes sense to anyone with even a vague notion of marijuana's effects. Pot is most popularly known as a sedative that relaxes users. One of the prominent arguments against its use, in fact, is that it makes users so sedated that they're lazy and, as a result, unproductive.

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