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Weed May Make People With Serious Mental Health Issues More Violent

A new study has found a link.

Today in weed stories that probably don't apply to you, casual smoker, but are interesting nonetheless—researchers from Montréal have found a link between sustained cannabis use and violent behaviour in young people. However, there's one important caveat: these young people (1,136 of them aged between 18 to 40 years old) were monitored after they were released from a psychiatric hospital.

So were these patients just already enough of a risk to themselves or others to end up in psychiatric care? Could they possibly be smoking to self-medicate? As the study notes, "Several studies… [have looked into] whether involvement in violence may cause cannabis use or vice versa or whether they are intertwined in a more complex manner." But working out whether weed is causing a jump in violent behaviour—if there's a causal relationship between the two—is a complicated question.


To unpack it, Dr Alexandre Dumais from the Institut Philippe Pinel and Dr Stéphane Potvin from the University of Montréal followed their cohort for a year after they were discharged from hospital. Patients were seen five times during that period—and asked about their substance use and any violent behaviour.

According to the study, the risk of violent behaviour for patients who reported at each of the five follow ups that they continued to use cannabis was 2.44 times higher than those who didn't report smoking. "An interesting feature of our results is that the association between persistent cannabis use and violence is stronger than that associated with alcohol or cocaine," Dr Dumais said.

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An obvious limitation of the study was that the researchers were relying on the patients to self-report both their cannabis use and violent behaviours accurately and honestly. The researchers also didn't take into account how much weed people were smoking or how often, or the cannabidiol (CBD)/tetrahydrocannabinol (THC) ratio of the cannabis consumed.

Then there's the fact the patients studied were overwhelmingly white (69.3%) men (58.7%) who were either single, separated, or divorced (86.7%). Moreover, about one-fifth of the sample were affected by schizophrenia spectrum disorders, which makes people "significantly more likely to be violent than other members of the general population." Other research suggests cannabis that's high in CBD and low in THC may actually help treat psychosis.

So what's the key takeaway here? Well, this study sheds light on the association between cannabis and violence in people who've been hospitalised for mental illness. The researchers believe there is a unidirectional relationship between the two—that chronic cannabis use is associated with increased violent behaviour. There are some interesting asides here as well, such as the fact alcohol remains a significant risk factor, but cocaine use isn't.

Overall though, we need a more complicated model to understand why recently discharged patients who smoke weed present a higher risk of violence. Headlines like "Smoking cannabis DOES make people more violent: Project confirms for the first time that using the drug is the cause of crimes" massively oversimplify a complicated relationship, and undermine the efforts of researchers who actually want to help those with mental health disorders—rather than just demonising drug use on the back of preliminary findings.

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