Problematic drug use population — an overview of the methods and definitions used

‘Problem drug use’ is defined by the EMCDDA as ‘injecting drug use or long duration / regular use of opioids, cocaine and/or amphetamines’. This definition specifically includes regular or long-term use of prescribed opioids such as methadone but does not include their rare or irregular use nor the use of other drugs, such as ecstasy or cannabis. Existing estimates of problem drug use are often limited to opioid and poly-drug use. As a reaction to a growing stimulants problem as well as a growing number of cannabis-related treatment demands, the EMCDDA is currently promoting estimates by main drug, as well as the best way of estimating the populations of intensive and/or long-term, possibly dependent or problematic, users of cannabis and other drugs or user groups which might not fall under the current PDU definition. Another line of work is looking into the conceptual background and potential operationalisation of the current definition (e.g. defining 'regular' and 'long-term' elements of the definition).

The methods used to produce prevalence estimates are based mainly on statistical models using drug use related indicators and include mainly:

• a simple multiplier method using police, treatment, mortality or HIV/HCV data, etc.;
• capture–recapture methods;
• extrapolation via multivariate indicator methods

The EMCDDA has produced guidelines for prevalence estimation (Guidelines for the prevalence of problem drug use (PDU) key indicator at local level and Guidelines for the prevalence of problem drug use (PDU) key indicator at national level), which are currently being updated also on the basis of the experience in the Member States, changes in the drug situation picture and improvements in methodology and data availability and quality.

Given the methodological improvements over the last few years, in many countries, it seems now possible to distinguish between injecting drug users (estimates from overdose mortality or HIV multipliers; these may be mainly current injectors) and the wider group of problem drug users, which includes both injectors and non-injectors.

Available estimates are improving in number and quality, but there are still many problems to be solved. There is no single method that can be applied in all the countries to give truly comparable results and even if a standard method such as capture-recapture can be used at local level, available datasets often differ so much that it would be difficult to compare results across countries. Comparability problems also stem from differences in the exact definition of the estimated target group, due to differences in drug use patterns between countries and case definitions which are possible to be used in estimation at the level of data sources used.

Most EU countries were able to produce national estimates of problem drug use – using the agreed definition of problem drug use – by 2010, although the availability of estimates of injecting drug use remains lower than desirable. Many of the available estimates are based on results from more than one estimation method, thereby adding to their reliability.

In addition to local and national prevalence estimation, several countries have been able to explore incidence estimation (time trends in numbers of new cases rather than static estimates of all existing cases) and guidelines have been prepared based on two different methods for estimating incidence. In recent years, novel methods are being developed and tested in countries with available data and which are interested.

References

EMCDDA Key Indicators Toolbox: PDU

Scalia Tomba GP, Rossi C, Taylor C, Klempova D, Wiessing L. (2008) Guidelines for

Estimating the Incidence of Problem Drug Use. EMCDDA, Lisbon.

Smit F, van Laar M, Wiessing L. Estimating problem drug use prevalence at national level: comparison of three methods. Drugs: education, prevention and policy 2006; 13: 109-20.

Aceijas C, Friedman SR, Cooper HLF, Wiessing L, Stimson GV, Hickman M. Estimates of injecting drug users at the national and local level in developing and transitional countries, and gender and age distribution. Sex Transm Infect 2006;82(Suppl III):iii10-iii17.

EMCDDA and Institut für Therapieforschung. Recommended Draft Technical Tools and Guidelines - Key Epidemiological Indicator: Prevalence of problem drug use. Lisbon: EMCDDA, 2004.

EMCDDA and Centre for Drug Misuse Research. Methodological Guidelines to Estimate the Prevalence of Problem Drug Use on the Local Level. EMCDDA Scientific Report CT.97.EP.05. Lisbon: EMCDDA, 1999.

EMCDDA and University of Tor Vergata. Draft Guidelines for Estimating Incidence. Lisbon: EMCDDA, 2004.

Kraus L, Augustin R, Frischer M, Kümmler P, Uhl A, Wiessing L. Estimating prevalence of problem drug use at national level in countries of the European Union and Norway. Addiction 2003; 98: 471-85.

Smit F, Toet J, van Oers H, Wiessing L. Estimating Local and National Problem Drug Use Prevalence from Demographics. Addiction Research and Theory 2003; 11: 401-413.

Frischer M, Hickman M, Kraus L, Mariani M, Wiessing L. A comparison of different methods for estimating the prevalence of problematic drug misuse in Great Britain. Addiction 2001; 96: 1465-1476.