AbstractIntroductionFamily members affected by another's substance use disorder experience physical health problems, breakdowns in relationships and reduced psychological wellbeing. This review examines the effectiveness of psychosocial interventions for improving the wellbeing of family members.MethodsA systematic review of randomised‐controlled trials (RCT), non‐RCTs and pre‐post studies examining group or individual interventions for affected families. Five databases were searched (PubMed, PsycINFO, Medline, Web of Science, Cochrane Library). Outcomes included psychological functioning, quality of life, physical health and substance use, family functioning and coping. Outcomes were analysed by study design and mode of delivery (individual or group). Risk of bias was assessed using the Cochrane tools (RoB2, ROBINS‐I). The review followed PRISMA reporting guidelines and was prospectively registered with the PROSPERO database (CRD42020200260).ResultsNineteen studies were included (k = 10 included in meta‐analyses). In k = 3 RCTs, individually administered interventions significantly reduced depression (standardised mean difference [SMD] 0.50, 95% confidence interval [CI] 0.21, 0.79) and distress (SMD 0.28, 95% CI 0.03, 0.54). In k = 2 pre‐post studies, individual interventions improved family functioning (d = 0.51, 95% CI 0.28, 0.73) and coping (d = 0.43, 95% CI 0.24, 0.61). In k = 3 non‐RCTs and k = 2 pre‐post designs group interventions significantly reduced depression (d = 0.50, 95% CI 0.17, 0.82) and distress (d = 0.44, 95% CI 0.13, 0.75), and improved coping (d = 0.81, 95% CI 0.29, 1.33).Discussion and ConclusionsThis review summarises the contemporary literature evaluating interventions for affected families, with both individual and group interventions demonstrating favourable outcomes. However, small sample sizes and methodologically weak‐quality studies limit conclusions.