Clinical effectiveness of internet-delivered self-help Aacceptance and Commitment Therapy for family carers of people with dementia (iACT4CARERS): a multicentre, parallel, randomised controlled trial.

Background: As dementia prevalence rises globally, unpaid family carers provide most care and face high mental health risk. Existing psychological interventions offer limited benefit for anxiety in this population. We evaluated the effectiveness of an internet-delivered, self-help Acceptance and Commitment Therapy intervention with minimal non-expert therapist support (iACT4CARERS) to reduce anxiety in dementia family carers. Methods: We conducted a multi-site, single-blind, parallel-group, randomised controlled trial across UK national healthcare services. Eligible participants were family carers of a person with dementia and reported anxiety symptoms (Generalised Anxiety Disorder-7 [GAD-7] score ≥5). Participants were allocated (1:1) to iACT4CARERS plus treatment-as-usual or treatment-as-usual alone, using computer-generated randomisation with minimisation by ethnicity and baseline anxiety. The intervention comprised an eight-session self-help programme guided by non-expert therapists. Outcome assessors and the lead statistician were blinded to allocation. The primary outcome was anxiety symptoms, assessed using the GAD-7 at 12-weeks post-randomisation. Analyses followed the intention-to-treat principle using linear regression models. The trial was pre-registered with ISRCTN (45995725). Findings: Between November 1, 2023, and January 14, 2025, 902 individuals were referred: 567 (63%) were assessed for eligibility and 496 (87%) were randomised (249 to intervention; 247 to control). 397/496 (80%) were female. Primary outcome data were available for 398/496 participants (80%). After adjustment for baseline anxiety, ethnicity, and education, iACT4CARERS plus treatment-as-usual significantly reduced anxiety at 12 weeks compared with treatment-as-usual alone (adjusted mean difference -2.62, 95% CI -3.47 to -1.77; p < 0.0001; d = 0.53), with participants in the intervention group showing clinically meaningful improvement. Three non-intervention-related adverse events were reported; no serious adverse events occurred. Interpretation: iACT4CARERS is an effective intervention for reducing anxiety symptoms and addressing a major unmet mental health need in this population, with strong potential for scalable implementation. Funding: National Institute for Health and Care Research Health Technology Assessment.