Claim: Cannabis use causes a quarter of psychosis cases.
Fact-check: Factcheck: does cannabis cause a quarter of psychosis cases? - Full Fact
Verdict: that's not what the research shows. high-potency cannabis  is linked to 24% of cases in south london, but that's not representative of the rest of the country.
Organisation: Full Fact
Author: Laura O'Brien
Date published: 2015-02-17T00:00:00