Abstract: The prescription of substitution drugs, such as methadone and buprenorphine, has become a mainstream, first-line treatment for opioid dependence, with around 700 000 of Europe’s 1.3 million problem opioid users receiving substitution treatment today. But a small minority of entrenched opioid users repeatedly fails to respond to interventions of this kind. Findings from international trials now suggest that the supervised use of medicinal heroin can be an effective second-line treatment for this small, and previously unresponsive, group. In this latest EMCDDA Insights report, experts describe the development as “an important clinical step forward”. The report provides the first state-of-the-art overview of research on the subject, examining the latest evidence and clinical experience in this area in Europe and beyond.