Your article correctly raised concerns about the harms of higher-strength cannabis on people vulnerable to psychosis (‘I’d run down the road thinking I was God’: a day at the cannabis psychosis clinic, 16 November). However, it didn’t explain how previous prohibition‑based policies designed to reduce cannabis use have driven up the strength of street cannabis, the source of most cannabis for people with psychosis, thus making the problem worse.

Furthermore, growing data from the Drug Science T21 project and other prescription databases globally shows that medical cannabis can alleviate a range of psychiatric and neurological disorders, without inducing psychosis. Any suggestion that rates of cannabis-related psychosis could be reduced by limiting medical cannabis access is flawed and is likely to harm patients currently benefiting from it.
Prof D Nutt and Prof Ilana Crome
Drug Science