LAUSR

223 strength and prevalence – cannabis use. The worldwide trend towards increasing use of cannabis, especially of high potency varieties, cries out for a preventive approach. A trans-European study estimated that, in London and Amsterdam, 30% and 50% of new cases of psychosis, respectively, would be prevented if no one smoked highpotency cannabis. The risk of developing psychotic disorder was increased 5-fold in those with daily use of high-potency cannabis compared with those who did not use cannabis. This is a similar effect size as between asbestos and lung cancer, but the outcome is much earlier in life. We cannot just wait in our units and emergency departments to treat the increasing numbers of young people with cannabis-related psychosis. There is much to learn from the public education programme implemented in Iceland over the last 20 years, with remarkable decreases in rates of alcohol consumption and tobacco and cannabis smoking among young people. It is time for mental health professionals to speak up about the risks of heavy use of cannabis on rates of psychosis and other mental health problems. It is time to move out of the clinic, remove the handle from the pump, and embrace the challenge of public health psychiatry.