Objective: The article describes an epidemiological indicator called Treatment Demand Indicator (TDI). The TDI aims to provide professionals and researchers with a common European methodology for collecting and reporting core data on drug users in contact with treatment services. The article discusses the implementation of the TDI in the European countries and describes the main results, limitations, and future perspectives.

Method: The TDI provides a common format for reporting data on clients entering treatment as a result of their drug use and related problems during each calendar year. Its technical protocol defines which clients should be reported at European level and represents the minimum common set of items each national monitoring system should be able to report to the European Monitoring Centre for Drugs and Drug Addiction.

Results: In 2015, 29 European countries reported data on 467,811 clients entering drug treatment from 6,846 drug treatment units. Most clients were men in their 30s and had problems related to heroin or cannabis use; patterns of drug use differed geographically. Over the past decade, clients’ profiles and drug use patterns changed from young heroin injectors seeking treatment to drug clients with diversified drug use patterns and profiles.

Conclusions: The TDI is the largest drug dataset in Europe, and its data is increasingly used in European and national data analysis. The use of a common drug-treatment-monitoring tool across a group of countries provides a useful instrument for policymakers, professionals, and managers working in the drug treatment field.