Objective The aim of our research was to assess the feasibility and efficacy of a treatment assisted by diacetylmorphine in Liège. This treatment is offered to persons dependent on heroin who pursue street heroin use despite existing treatments. Methods Data were collected in a pilot project of Treatment Assisted by Diacetylmorphine (TADAM), which took place in Liège from 2007 to 2013. The heart of this project is a randomised controlled trial comparing a diacetylmorphine treatment – limited to 12 months – with existing methadone treatments. A participant was responder if he/she showed improvement on the level of street heroin use, health or criminal involvement. Other researches (mainly based on interviews) were added in order to understand interactions between the trial and its actors: heroin users (included or not-included), neighbours of the DAM centre, the staff of the DAM centre and staff of other institutions who worked with our target group in Liège. Results With the help of the centres, partners of the trial, 74 participants (of the 200 planned) were included and randomised: 36 in the experimental group and 38 in the control group. These participants were dependent on heroin for 20 years on average and had already tried 9 treatments for their addiction(s). At the end of the trial, the number of responders in the experimental group was greater but not significantly than in the control group (p=0.35). However, participants in the experimental group showed greater improvement than in the control group, on the level of street heroin use (p=0.0011) and physical (p=0.043) or mental (p=0.035) health. During the follow-up study, three months after the end of the 12 months of treatment, street heroin use in the experimental group had significantly increased (p=0.0052) and the difference with the control group was no longer significant (p=0.55). Discussion Participants included in the trial were, as expected, persons severely dependent on street heroin, who could not find a solution to their addiction with the ...