An enlarged EMCDDA Scientific Committee met from 18–19 May 1997 in Lisbon to assess the risks of the synthetic drug 4-MTA (4-methylthioamphetamine) in the framework of the Joint action on new synthetic drugs. The Committee's tasks were to assess the health and social risks of the substance and the possible consequences of prohibition. This report concludes that 4-MTA should be placed under control in the EU Member States largely due to the high risks of overdose associated with the drug. These stem from the slow onset of the drug's effects – often misinterpreted by users as the result of a weak dose, leading to the consumption of more pills – and their long-lasting nature. Also highlighted in the report are the serious risks resulting from mixing the drug with alcohol, MDMA, amphetamines, ephedrine and certain foods. Further to the conclusions of the EMCDDA risk assessment, on 13 September 1999, the Council of the European Union adopted a unanimous decision defining the new synthetic drug 4-MTA (4-methylthioamphetamine) as a substance to be placed under control measures and criminal penalties in the EU Member States.