High-strength cannabis linked to psychosis

People who use high-strength cannabis may be at increased risk of developing serious mental health issues, according to new research.

The study, outlined in a paper in The Lancet Psychiatry journal, found that an estimated one in ten new cases of psychosis may be associated with strong cannabis.

And “in London and Amsterdam, where most of the cannabis that is sold is very strong, the risk could be much more”, reports the BBC.

Subscribe to The Week

Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives.

SUBSCRIBE & SAVE

Sign up for The Week's Free Newsletters

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox.

Sign up

The researchers, who looked at data from 11 European cities and towns, estimated that 30% of first-time cases of psychotic disorders in London, and half of those in Amsterdam, could be avoided if high-potency cannabis was not available.

The findings back up those of other experts who “have previously flagged a link between cannabis use and psychosis, particularly among vulnerable people with heavy use of the drug”, says The Guardian.

“If you are a psychologist like me who works in this catchment area and sees first-episode psychosis patients, this has a significant impact at the level of services and, I would also argue, family and society,” said Dr Marta Di Forti, lead author of the new study, from King’s College London.

“If you decide to use high-potency cannabis bear in mind there is this potential risk,” she added.

High-strength cannabis, such as that known as “skunk”, has levels of the psychoactive substance tetrahydrocannabinol (THC) above 10%. According to data released last year, 94% of police cannabis seizures in the UK were of high-strength varieties.

The new study found that daily cannabis users in Amsterdam were seven times more likely to develop a psychotic disorder than people who had never used the drug. “Almost all cannabis sold in ‘coffee shops’ in Amsterdam is high-strength, while varieties with 67% THC have been found in the Netherlands,” notes The Guardian.

Study-co-author Professor Robin Murray said the research had implications for the debate on whether cannabis should be legalised.

“If you are going to legalise cannabis, unless you want to pay for more a lot more psychiatric beds and a lot more psychiatrists, then you need to devise a system where you would legalise in a way that wouldn’t increase the consumption and increase the potency,” he said.