Donaldson, Jessica L.Robertson, Alysia M.Cruwys, TeganRathbone, Joanne A.Haslam, CatherineChen, JunwenDawel, Amy2025-07-082025-07-080144-6657WOS:001492418300001ORCID:/0000-0002-3803-2492/work/185910238ORCID:/0000-0003-4870-750X/work/185910535ORCID:/0000-0001-6668-3121/work/185913346ORCID:/0000-0001-5296-3480/work/185914410https://hdl.handle.net/1885/733766179Objectives: Current best-practice treatments for social anxiety disorder do not directly address loneliness, despite its role in the maintenance of the condition. The current study targets this issue directly, using mixed methods to provide an initial test of the efficacy of an established loneliness intervention, Groups 4 Health (G4H), among 33 people with clinically elevated social anxiety symptoms.  Design: A single-arm design was used and outcomes were assessed at baseline, programme completion and 5-month follow-up (3 months after programme completion).  Methods: Loneliness, social anxiety symptoms, depression symptoms and well-being were assessed at each time point. Semi-structured follow-up interviews were also conducted to explore the feasibility and acceptability of G4H in this population.  Results: Results from intention-to-treat analyses provide initial evidence of the programme's efficacy: participants' loneliness (d = −1.08), social anxiety symptoms (d = −.45), and depression symptoms (d = −.60) reduced significantly from baseline to 5-month follow-up while their well-being (d = 1.00) increased. Four themes emerged from reflexive thematic analysis: (1) the importance of challenging initial anxiety about attending group therapy, (2) the value of being vulnerable with fellow group members, (3) the role of G4H in increasing participants' social confidence, and (4) processes which both helped and hindered participants' ability to engage with their group.  Conclusions: Together, results suggest that G4H is a promising and innovative treatment option for people with social anxiety, and further controlled evaluation is warranted.This project was supported by Australian Government Research Training Program (RTP) Scholarships awarded to Jessica L. Donaldson and Alysia M. Robertson, a National Health and Medical Research Council Fellowship (NHMRC; #1173270) awarded to Tegan Cruwys, and philanthropic support from Susan and Stuart Lloyd-Hurwitz. The funders had no role in the study's design, data collection, analysis, and interpretation, the preparation of this manuscript, or the decision to publish. We would like to thank the ANU Psychology Clinic, our group facilitators, and our participants, without whom this research would not have been possible. Open access publishing facilitated by Australian National University, as part of the Wiley - Australian National University agreement via the Council of Australian University Librarians.23en© 2025 The Author(s). British Journal of Clinical Psychology published by John Wiley & Sons Ltd on behalf of British Psychological Society.group membershipsgroup psychotherapylonelinessmental healthsocial anxietysocial identitysocial isolation2025-05-2110.1111/bjc.12539105005839119