Bowring, Anna L.Tidhar, TomOlsen, AnnaBailie, ChristopherBurke, KelvinMartin-Hughes, RowanKeane, HelenDietze, PaulScott, Nick2026-02-262026-02-260965-2140WOS:001671614300001ORCID:/0000-0002-8712-3390/work/206440253https://hdl.handle.net/1885/733806676Background and aims: Harm reduction interventions aim to reduce negative consequences of drug use. We aimed to estimate the cost, health impact and economic benefits of current, expanded and new harm reduction interventions for people who use drugs in the Australian Capital Territory.  Design: We conducted a cost–benefit analysis of existing and new harm reduction interventions in the Australian Capital Territory. Independent decision tree models captured health outcomes [opioid/non-opioid overdose; overdose-related deaths; injection-related skin/soft tissue/vascular infections (IRIs); hepatitis C incidence] for 2026–2030 according to intervention coverage.  Setting: Australian Capital Territory, Australia.  Participants/cases: People who use drugs through injecting (n = 1500) or non-injecting (n = 33 600) routes differentiated by drug class (opioid/non-opioid).  Interventions and comparator: A baseline scenario (current intervention coverage maintained) was compared with a counterfactual no interventions scenario, as well as scenarios with interventions linearly scaled up to the assumed maximum proportion of the target population that could be reached given geographical, social and implementation constraints. Interventions included in the analysis were: drug consumption rooms, needle-syringe programs, take-home naloxone, opioid agonist treatment, safer opioid supply, drug checking services and technological interventions (i.e. overdose monitoring ‘apps’/hotlines).  Measurements: Economic benefits were estimated from health costs averted (emergency response; shorter hospitalisation for IRI; hepatitis C treatment) and societal costs from years of life lost. Benefit–cost ratios were calculated compared to the baseline. A sensitivity analysis considered a changed illicit drug market with increased probability of overdose and overdose-related death.  Findings: Compared with no coverage, the current package of harm reduction interventions was estimated to cost $24.6 million over 2026–2030 and avert 454 (24%) opioid and 20 (0.2%) non-opioid overdoses, 70 (28%) overdose-related deaths, 215 (17%) emergency responses, 552 (117%) hepatitis C infections and 199 (9%) IRIs. This corresponds to $250.1 million in economic benefits [benefit–cost ratio = 10.1, 95% confidence interval (CI) = 7.9–12.4]. Benefit–cost ratios for scaling up take-home naloxone [16.4 (5.0–27.9)], opioid agonist treatment [10.2 (5.6–15.3)], technological interventions [3.5 (0.0–15.7)], drug consumption room/s using medialised [1.9 (0.6–3.9)] or nurse/peer-led model [2.7 (1.2–4.4)], safer opioid supply [1.5 (0.8–2.6)] and needle-syringe programs [1.4 (0.7–2.6)] were favourable. The benefit–cost ratio for drug checking was 0.3 (0.0–6.2) but increased to 14.0 (0.1–29.6) under changed drug market conditions.  Conclusions: Modelled expanded and new harm reduction interventions for people who use drugs in the Australian Capital Territory appear to be likely to be cost saving from a societal perspective. If circulation of drugs with higher overdose risks was greater in this region, this would increase the impacts of interventions to prevent overdose and associated harms.This analysis was conducted as a collaboration between the Australian National University and the Burnet Institute with funding support from the ACT Health Directorate. The authors also gratefully acknowledge the contribution to this work of the Victorian Operational Infrastructure Support Program received by the Burnet Institute.18en© 2025 The Author(s). Addiction published by John Wiley & Sons Ltd on behalf of Society for the Study of Addiction.drug consumption roomshepatitis Cnaloxoneneedle and syringe programsopioid agonist treatmentopioidsoverdosepeople who inject drugsskin infectionssubstance use202610.1111/add.70276105028976929