peer reviewed ; Background/Aims: Heroin-assisted treatment (HAT) can improve the condition of heroin addicts still using street heroin after a methadone treatment. In Belgium, a new trial compared the efficacy of a HAT to existing methadone maintenance treatment. Methods: In this randomised controlled trial, HAT was limited to 12 months. Participants were assessed every 3 months. They were responders if they showed improvement on the level of street heroin use, health or criminal involvement. Results: 74 participants were randomised in the trial. The experimental group (n=36) counted 30% of responders more than the control group (n=38) at each assessment point (p<0.05), except at 12 months where the difference (11%) was no longer significant (p=0.35). Still, after 12 months, participants in the experimental group reported significantly greater improvements (p<0.05) than the control group on the level of street heroin use and on the level of physical and mental health. Both groups reported significantly less criminal facts after 12 months (p<0.001), but with no significant difference between the groups. Conclusions: This trial confirms the short-term efficacy of HAT for severe heroin addicts, who already failed methadone treatment. ; TADAM, un projet pilote de traitement assisté par diacétylmorphine (héroïne pharmaceutique)