Methodological note: Analysis of trends is based only on those countries providing sufficient data to describe changes over the period specified. The reader should also be aware that monitoring patterns and trends in a hidden and stigmatised behaviour like drug use is both practically and methodologically challenging. For this reason, multiple sources of data are used for the purposes of analysis in this report. Caution is therefore required in interpretation, in particular when countries are compared on any single measure. Detailed information on methodology and caveats and comments on the limitations in the information set available can be found in the EMCDDA Statistical Bulletin.