ROYAL GORILLA, Girl Scout Cookies and Fat Banana are just a few of the improbably named strains of high-potency cannabis out there. In the former, levels of tetrahydrocannabinol (THC), the chemical behind the psychological effects of cannabis, are above 25%. Reviewers describe it as “overwhelming” for novices and a “beautiful euphoric couch-locking experience” for others.
However enticing that may sound, regular use of cannabis with a potency greater than 10% increases the risk of developing psychosis five-fold, according to a study published this week by the Lancet. It also found that using less potent strains daily increased the risk three-fold. Marta Di Forti, a clinical scientist at Kings College in London, and her colleagues looked at cannabis use among 901 European patients newly diagnosed with psychosis. A non-smoking control group was recruited from the general population.
The study adds substantial weight to the evidence linking cannabis to the onset of psychosis. It also suggests that differences between varieties and how often they are used could help explain why rates of psychosis among cannabis users vary across Europe.
Other factors, including genetic susceptibility, stress and injury, are also thought to be at work. Nonetheless, a growing body of evidence makes it likely...