Abstract: This publication presents the summary findings and the conclusions of the risk assessment on mephedrone, carried out by the EMCDDA’s extended Scientific Committee, with participation of additional experts from the European Commission, Europol and the EMA. The risk assessment report, which was submitted to the European Commission and the Council of the European Union 26 May 2010, examines the health and social risks of the drug, as well as information on international trafficking and the involvement of organised crime. Furthermore, the report considers the potential implications for placing the drug under control in the EU. On the basis of this report – and on the initiative of the European Commission – on 2 December 2010, the Council decided that mephedrone is to be subject to control measures.