Self-harm before and during imprisonment: cohort study of males in prison linking population-based routinely collected data in Wales

Pre-imprisonment, self-harm in male prisoners is already high compared with the general population, potentially driving a saturation effect, where known general population risk factors have a weaker effect in prisoners. Self-harm prevention should target people in contact with criminal justice, irrespective of imprisonment. In prisons, prevention efforts deployed at inception should target those with prior self-harm, drug use, learning difficulties, bipolar disorder and those on remand.