Groups for belonging: a parallel cluster randomized controlled trial of a group-based loneliness intervention for people attending treatment for alcohol and other drug use.

Background: People accessing alcohol and other drug (AOD) treatment experience high rates of loneliness, which is a strong driver of substance use. Groups for Belonging is a 6-session group-based intervention that combines elements of the social identity informed intervention Groups for Health with psychoeducation and strategies to help participants manage loneliness and overcome cognitive barriers to social connection. The project will examine the effectiveness and cost-effectiveness of delivering Groups for Belonging within routine care offered by AOD treatment providers in Australia.

Methods: Participants will be adults attending residential or community-based AOD treatment provided by either public sector or non-government treatment providers across New South Wales (NSW), Victoria (VIC), Queensland (QLD) and the Australian Capital Territory (ACT) in Australia. The study will be conducted as a parallel cluster randomized controlled trial (RCT), involving 26 clusters (13 treatment, 13 control, N = 520), with randomization occurring at the service level. Depending on randomization, participants will either complete treatment as usual (i.e., AOD treatment provided by participating services) or Groups for Belonging and treatment as usual.

Discussion: This study aims to determine the effectiveness of a loneliness intervention, Groups for Belonging, for people accessing residential and community-based treatment for AOD use. If the intervention is effective and cost-effective, implementation efforts will focus on embedding the intervention into routine care in AOD treatment services across metropolitan and regional areas in Australia. This has significant potential to decrease loneliness and its associated effects on health and wellbeing for people accessing AOD treatment.

Trial Registration: Australia and New Zealand Clinical Trials Registry, CTRN12625000132448 ( https://www.anzctr.org.au/ACTRN12625000132448.aspx ). Registered on 6 February 2025.