The use of cannabis in young people is an independent risk factor for the development of incident psychotic symptoms, a prospective cohort study has found. Data were analysed on 1,923 subjects drawn from the Early Developmental Stages of Psychopathology Study in Germany. Participants were aged 14-24 years, mean 18.3, at entry and followed up for 10 years. Dr Jez Thompson writes: 'The authors conclude that cannabis is a risk factor for the development of incident psychotic symptoms and that continued use of cannabis might increase the risk of psychotic disorder by impacting on the persistence of normally transitory psychotic symptoms in young people.'