Although there is ample evidence linking marijuana and psychosis, a new study in The Lancet Psychiatry is the first to show the impact on population rates of psychosis. Reuters reports “one in five new cases of psychosis across the sites studied could be linked to daily cannabis use, and more than one in 10 linked to use of high-potency cannabis. This would mean that if high potency cannabis were no longer available, the incidence of psychosis in Amsterdam, for example, would be expected to drop to 18.8 from 37.9 per 100,000 people a year, and in London to 31.9 from 45.7 per 100,000 people a year.”