Background <p>People with dementia often need comprehensive support, depending on the stage of the disease, from both family members and healthcare professionals. Caring for a person with dementia can be stressful and impact the caregiver’s health and wellbeing. Studies show that family caregivers of people with dementia frequently experience stress, depression, and reduced quality of life. We aimed to assess the association between the psychosocial intervention (DemTool) and caregiver wellbeing and quality of life among family caregivers of people with dementia.</p> Method <p>DemTool trial was a pragmatic, cluster-controlled trial. The intervention was delivered by primary care dementia coordinators across 30 Danish municipalities from 2020 to 2023, with 15 serving as the intervention group and 15 as treatment as usual. The primary outcome measures were the Neuropsychiatric Inventory Caregiver Distress Scale (NPI-D) and the European Quality of Life Visual Analog Scale (EQ VAS). Both measures were completed at baseline and follow-up, alongside secondary quality of life outcomes. To estimate group differences in primary and secondary outcomes, we applied analysis of variance (ANOVA) and analysis of covariance (ANCOVA).</p> Results <p>A total of 245 family caregivers were included in the study (181 in the intervention group and 64 in the treatment-as-usual group). Most participants were females caring for a spouse. Baseline scores for caregiver wellbeing and quality of life were similar across groups. The DemTool intervention was associated with a significant between-group difference in change from baseline in caregiver-related quality of life as measured by the Carer Experience Scale (CES), favoring the intervention. This was evident in the analysis adjusted for baseline scores (<i>p</i> = 0.05) and remained significant when further adjusting for caregiver-related covariates (<i>p</i> = 0.02). No statistically significant between-group differences were observed for the remaining wellbeing and quality-of-life outcomes.</p> Conclusion <p>No effects of DemTool were found on traditional health-related quality-of-life outcomes. However, a positive association was found between the intervention and the CES, underlining the importance of selecting outcomes that are directly related to the targeted effects of the intervention.</p> Trial registration <p>The study protocol was registered in the ClinicalTrials.gov system, registration number: NCT07355829.</p>