The study was conducted according to an organizational structure which involved participating groups on the national and city level. The responsibilities of the participating groups/participants are outlined below:

- The Ministry of Health, Welfare, and Sports commissioned and sponsored the study.
- The Central Committee on the Treatment of Heroin Addicts (CCBH), installed by the Minister of Health, Welfare and Sports to develop and conduct the study, was responsible for the development, conduct and scientific quality of the study. The CCBH reports directly to the Minister of Health, Welfare and Sports. The composition of the CCBH and the expertise represented in the CCBH, are outlined in Appendix 3.
- The National Research Board, headed by the research director, was responsible for all technical and scientific aspects of the study, including the analysis of the collected data, and for the co-ordination of the treatment sites, monitoring, data collection and reporting of the study findings (Appendix 4). The National Research Board reports to the CCBH, and - with regard to the medical safety and public order issues - to the LVC and LCB, respectively.
- The Inspectorate of Health Care observed and examined the quality of the care provided and the way and accuracy of registration of the prescribed heroin (drug accountability). The Inspectorate advised the CCBH, and was present as observer during the meetings of the CCBH.
- The National Safety Committee (LVC) advised the CCBH, with regard to the evaluation of severe adverse events and other medical safety issues (Appendix 4). This committee could also advise about possible premature termination of the study in case of a medically unacceptable negative balance between effectiveness and harm. The findings of the LVC with regard to the test period of the study were reported to both the CCBH, and the Minister of Health, Welfare and Sports.
- The National Committee on Public Order and Controllability (LCB) advised the CCBH, with regard to the evaluation of public order and public safety issues (Appendix 4). The findings of the LCB with regard to the test period of the study were reported to both the CCBH, and the Minister of Health, Welfare and Sports.

Figure 3. Organization of the study

- The draft national study protocol was submitted by the CCBH to independent international scientific advisors (Appendix 5).
- The national study protocol was submitted by the Minister of Health, Welfare, and Sports to the Central Committee on Medical Ethics of the Netherlands, and was approved by this committee. In addition, amendments to the protocol made in the course of the study were all submitted to, and approved by this committee.
- The local research teams were responsible for the collection of data on the local level, in compliance with the national study protocol. In this capacity, they operated independently from the local treatment sites. In each study site, a local study co-ordinator was appointed.
- The local treatment sites were responsible for the treatment with heroin and/or methadone, in compliance with the national protocol. The National Research Board monitored, through independent monitors, the execution of the treatment protocol.
- The independent monitoring organization, appointed by the CCBH, monitored the data collection and the execution of the treatments. The monitoring in this study was conducted by Kendle. The data management was handled by Imro Tramarko Group. Both the monitoring organization and the data management organization reported to the National Research Board.
- The cities involved in the study developed a protocol with respect to aspects of public order and controllability, and made a contract with the Ministry of Health, Welfare and Sports, to conduct the study without impediments.