The National Treatment Outcome Research Study (NTORS) was a study carried out by the National Addiction Centre in England and Wales between the years 1995 and 2000 - the largest UK drug treatment outcome study at the time. This study followed up the clients of a variety of drug treatment service types for up to five years, examining a wide range of outcome measures via the Maudsley Addiction Profile (MAP) and was able to make a clear case for the effectiveness and cost-effectiveness of treatment.

Since NTORS clients were recruited in 1995/96, the UK has seen some major changes in treatment provision that made it necessary to reinvestigate the impact of different drug treatment pathways on treatment outcomes, including:

• the expansion of criminal justice routes into treatment
• an increase in the number of stimulant, especially crack users accessing treatment services
• an increased focus on the process of drug treatment
• a move towards an evidence-based treatment delivery process and introduction of the NTA's Models of Care (2002)