Cannabis users twice as likely to commit violence

Cannabis users are twice as likely to commit violent acts as those who do not take the illegal drug, according to new research.

Reviewing evidence from 63 peer-reviewed studies, researchers from Kings College London (KCL) found a “significant association between cannabis use and increased risk of violence”, though they were not able to establish causation.

The authors recommended that mental health professionals take the Class B drug into account when assessing patients for risk of violence.

Risks

Among people in psychiatric care, cannabis users were around two and a half times as likely to be violent as non-cannabis users.

In addition, the study found that cannabis users were around one and a half times as likely to be victims of violence.

Study co-author Dr Marta Di Forti said: “As a clinician, I’ve seen how heavy cannabis use can be a factor in violence.”

She added: “We’ve been cautious for a long time about how far we could go in describing this link, but a review of this size lets us speak with more confidence about the risks”.

Paranoia

Prof Sir Robin Murray of KCL’s Institute of Psychiatry, Psychology & Neuroscience said: “If cannabis does play a causal role, the most likely mechanism is that, as we know, heavy use of cannabis is associated with paranoia.

“Users are therefore more likely to misinterpret the actions or speech of others and conclude that they have bad intentions towards them. They may then attack people, believing they are protecting themselves.

“As cannabis becomes more commercialised and legalised around the world, the conversation about its risks has focused mostly on the person using it. This review shows that violence, both committing it and experiencing it, needs to be part of that conversation too.”

He stated: “My personal view is that wherever cannabis has been legalised in the Western world, use has increased, and so has potency”.