People who regularly smoke cannabis are nearly three times more likely to commit a violent offence than those who do not use the drug, new research has found.
The study, published in the American Journal of Psychiatry, analysed the link between violence and cannabis use in 30 studies involving almost 300,000 young people.
The team from the University of Montreal found that “persistent heavy users” of the drug were 2.81 times more likely to be violent than non-users, while less frequent users were still 2.15 times more likely to be violent.
The researchers concluded that their study “suggests that cannabis use appears to be a contributing factor in the perpetration of violence”.
Citing neurological research, they said that using the substance during adolescence may impair the brain structures which “limit one’s ability to suppress the urge to act out violently”.
The researchers reported that the “effect remained significant” even when taking into account that cannabis users may be more likely to grow up in violent surroundings.
Sir Robin Murray, a professor at the Institute of Psychiatry at King’s College London, said that the link between cannabis use and violence is a “neglected area”.
The professor said the study “is not a surprise for those of us who follow the scientific literature or see patients who heavily use cannabis.
“However, it may be a surprise to the many who think cannabis is a chill-out, anti-violence drug.”
In March it was revealed that a man with psychosis who stabbed five people in Edmonton, north London in 2019 had been smoking cannabis daily.
Jason Kakaire, 30, said voices in his head told him to kill people to prevent himself from being killed.
Kakaire said he recognised that regular cannabis use may have been the cause of some of the hallucinations.
Despite the dangers, pro-drugs campaigners in the UK regularly lobby for the legalisation of cannabis.