Using highly potent cannabis on a daily basis greatly increases the chances of a person developing psychotic disorders like schizophrenia and paranoia, according to a new study. Research published in The Lancet Psychiatry journal on Tuesday found that those who use “high potency” marijuana every day are four times more likely to suffer a psychotic episode than those who have never used the drug. The scientists behind the study defined “high potency” cannabis as any product containing more than 10 percent THC. London, Paris, and Amsterdam—places where high potency weed is more readily available—are said to have recorded higher rates of recent psychosis cases. The study found that one out of every five new cases of psychosis in 11 European cities, along with one in Brazil, were linked to the daily use of weed. One out of every 10 new cases were attributed to high potency cannabis. “This is more evidence that the link between cannabis and psychosis matters,” Krista Lisdahl, a clinical neuropsychologist at the University of Wisconsin, Milwaukee, who did not take part in the study, told NPR of the findings.