BackgroundAlthough depression is a common problem among non-professional caregivers, only one trial has evaluated the efficacy of indicated prevention targeting this population and the long-term efficacy is unknown. The aim of this study was to evaluate the long-term efficacy of a brief intervention for the indicated prevention of depression in a sample of female caregivers.MethodA randomized controlled trial was conducted involving 173 participants (mean age 53.9 years) who were allocated to the intervention (n = 89) or the usual-care control group (n = 84). Blinded interviewers conducted assessments at 1, 3, 6 and 12 months of follow-up. The main outcome measure was the incidence of major depression and the secondary outcomes were compliance with treatment, depressive symptoms, emotional distress and caregiver burden.ResultsAt the 12-month follow-up, a lower incidence of depression as evaluated using the Structured Clinical Interview for Axis I Disorders of the DSM-IV was found in the intervention group compared with the control group (10.1%v.25.0%). The relative risk was 0.40 and statistically significant [χ² = 6.68, degrees of freedom = 1,p = 0.010, 95% confidence interval (CI) 0.20–0.81], and the number needed to treat was 7 (95% CI 4–27). There was a significant delay in the onset of depression in the intervention group (p = 0.008). The good complier caregivers had a lower incidence of depression. The intervention effect on depressive symptoms, emotional distress and caregiver burden were maintained for 12 months.ConclusionsThis is the first study to demonstrate that a brief problem-solving intervention can prevent the onset of depression among non-professional caregivers over the longer term.