BackgroundStudies of psychological interventions for the prevention of depression have found significant effects in the short-term, but the long-term efficacy has yet to be determined. This study evaluated the 8-year effect of a randomized controlled trial for indicated prevention of depression in female caregivers.MethodsA total of 173 non-professional female caregivers with subclinical depressive symptoms not meeting criteria for a major depressive episode (MDE) were randomized to either a brief problem-solving intervention (n = 89) or usual-care control group (n = 84). Blinded evaluators conducted an assessment at the 8-year follow-up. The primary outcome was Depression Status, defined by diagnoses of MDE since the 1-year follow-up using the Structured Clinical Interview for the Disorders of the DSM-5. The secondary outcome was current Depressive Symptom Severity. Regression analyses were conducted to evaluate the effect of the intervention on the outcomes.ResultsThere were no significant differences in the Depression Status between the problem-solving (30.3%) and control groups (26.2%) (adjusted OR 1.25, 95% CI '0.58 to 2.69). Depressive Symptom Severity, however, was significantly lower in the problem-solving group compared to the control group at this follow-up, amounting to a small effect size of Cohen's d = 0.39 (adjusted B = '3.32, p = 0.018).ConclusionsThis is the first study to assess such a long-term follow-up of intervention of indicated prevention of depression. Results seem to indicate that the protective effect of the intervention became smaller over time during follow-up. Future research should replicate these results.