Balcaen, Margot and Deconinck, Eric and Lievens, Sybrien and Canfyn, Michael and Van Campenhout, Peter and Gremeaux, Lies (2026) What’s in your heroin? The importance of drug composition monitoring in the synthetic opioid era. Harm Reduction Journal, Early online, https://doi.org/10.1186/s12954-026-01502-1.