Alcohol use disorder (AUD) is a persistent public health concern, contributing significantly to mortality and morbidity. This study aims to evaluate the impact of in-hospital extended-release naltrexone (XR-NTX) administration on alcohol-related outcomes. This retrospective cohort study, conducted at an academic medical centre, included 141 adult patients with AUD who received XR-NTX between December 2020 and June 2021. Primary and secondary outcomes were assessed 90 days before and after XR-NTX administration to identify number of alcohol-related hospitalisations, emergency department (ED) visits and average length of hospital stay. Subgroup analyses assessed outcomes in high hospital utilisers and marginally housed or unhoused populations. There was a significant decrease in ED visits and length of hospital stay post XR-NTX and no significant difference in the number of rehospitalisations. Subgroup analysis showed significant reduction in hospital readmissions and ED visits among high hospital utilisers. Our sample was a predominantly middle-aged, male and white patient population. In-hospital initiation of XR-NTX for AUD was associated with a significant decrease in ED visits and length of hospital stay. While no significant impact on the number of hospitalisations was observed overall, there was a substantial reduction in hospital readmissions and ED visits among high utilisers. Our findings suggest the potential benefits of in-hospital XR-NTX, emphasising the need for further research to establish causal relationships, assess cost-effectiveness and explore effectiveness across diverse patient populations. Effective in-hospital interventions, such as XR-NTX, hold promise for improving patient outcomes and reducing the healthcare burden associated with AUD.