TREAT is a collaborative multi-centre-study conducted in Athens, Essen, London, Padua, Stockholm and Zurich which includes three repeated measures over a period of 18 month (T1-T3). Apart from the Europ-ASI, questionnaires for comorbid disorders and the utilisation of the treatment system were administered. The sample comprised about 100 subjects per region diagnosed with opiate addiction. 317 patients (53%) were retrieved for all three measures.

With some exceptions in all centres health service use by patients could be increased during the observation period. The severity of addiction decreased in almost all regions.

In a statistical model comprising all subjects who completed the study, the best predictor for abstinence was the number of detoxification treatments but also participation in long-term rehabilitative therapy. Patients with additional severe alcohol consumption at the beginning of the study had a higher risk for continuous drug use.

A second regression-model assumed that participants who had dropped out were still dependent on opiates. Again the combination of heroin and alcohol appeared to be a negative predictor. Patients in methadone maintenance treatment suffering from major depression showed a more positive outcome.

Regional differences concerning patients´ characteristics, health services and drop-out rates give reason for a cautious interpretation. The study describes high- and low-risk-groups as hints for the effective allocation of resources.