BACKGROUND Alcohol Assertive Outreach Treatment (AAOT) is designed to support individuals with alcohol use disorder who have complex needs that hinder successful engagement with specialist addiction treatment services, leading to greater unplanned healthcare utilization and mortality.

METHODS A convergent mixed-methods study to examine healthcare utilization, contextual factors, and engagement predictors among service users under AAOT. This includes a 12-month mirror-image analysis of healthcare and treatment engagement data for service users referred to AAOT between January 2018 - March 2022 ( = 1807), and qualitative interviews with service users ( = 18) and staff members ( = 20), to identify facilitators and barriers to engagement with AAOT, using framework analysis informed by the Consolidated Framework for Implementation Research.

FINDINGS Post-AAOT, emergency department attendances and unplanned ward admissions decreased significantly ( < 0.001). Number of contacts during AAOT predicted successful treatment completion ( < 0.001); while unemployed and long-term sick or disabled service users were less likely to have a successful outcome, ( < 0.01) and ( < 0.05), respectively. Four themes were developed from the qualitative study: (a) service users' challenges to engage with other services including stigma, (b) facilitators of their engagement with AAOT, (c) the intervention's relative advantage and d) reported outcomes following the intervention.

CONCLUSION Findings suggest an association between AAOT and reductions in unplanned healthcare utilization. Qualitative results indicate that AAOT has a relative advantage over interventions offered by specialist addiction treatment services due to the persistent, informal, outreach-based and person-centred approach adopted to engage a cohort facing complex and largely unmet needs.