Initiation, cessation and resumption of attendance at the Melbourne supervised injecting room among a cohort of people who inject drugs

• Half of the cohort initiated MSIR attendance during the study, indicating strong service uptake. Initiation rates exceeded cessation rates, with equal rates of cessation and resumption suggesting stable overall use. • MSIR attendance was more common among men, individuals with Aboriginal and/or Torres Strait Islander heritage, and those recently experiencing homelessness—groups often at higher risk of overdose and injection-related harm. • The service’s ability to engage clients with complex needs highlights its role in addressing health disparities and supporting people who may otherwise be underserved by traditional healthcare systems. • Participants prescribed opioid agonist therapy (OAT) were less likely to attend the MSIR frequently, likely reflecting lower injecting frequency and increased stability. Supervised injecting facilities (SIFs) reduce drug-related harms and associated costs, but evidence is limited to a few settings. This study estimates rates of initiation, cessation, and resumption of Melbourne’s Medically Supervised Injecting Room (MSIR) use among a cohort of people who inject drugs. Data were drawn from SuperMIX, an ongoing cohort study since 2008. Participants complete baseline and annual surveys, including MSIR use since its opening on 30 June 2018. We reported baseline characteristics and calculated incidence rates (IRs) of MSIR initiation, cessation, and resumption, stratified by recent homelessness and opiate agonist therapy (OAT) use, per 1000 person-years (PY). Of 1650 eligible participants, 685 (42%) reported MSIR use at baseline. MSIR attenders were slightly older (median 43 vs. 41 years) and less often female (28% vs. 35%) than non-attenders. Most (71%) were infrequent attenders (