Assessing the validity of recent estimates of problematic drug use in England.

BACKGROUND The Home Office has recently published estimates which, for the first time, provide a "robust national estimate" of the number of problematic drug users in England. The 2004/05 and 2005/06 estimates are the highest estimates ever produced for England and coincide with the highest ever government annual expenditure on combating illicit drug use. METHODS AND RESULTS Review of a range of data sources that indicate a downward trend in problematic drug use in recent years. CONCLUSIONS The validity of the estimates is important for drug policy, and the paper considers the implications of both increasing and decreasing levels of problematic drug use.