This 'Selected issue' looks at the concomitant or consecutive use of different licit and illicit drugs (polydrug use) among adolescents, young adults and problem drug users. Data from school and general population surveys, and on drug treatment entrants and drug-related deaths are analysed to describe the many forms and consequences of this widespread pattern of drug use. The responses to polydrug use in Europe are reviewed in the light of the scientific literature, with the aim of identifying the most effective interventions. An online annex provides links to additional tables and figures. A multilingual summary of the contents is available >>