Introduction: Major depression is a highly prevalent and heterogenous mental disorder. Although therapeutic advances for major depressive disorder over the past quarter-century have been incremental rather than transformative, booster sessions have been proposed as a means of solidifying acute treatment gains and lowering relapse risk. However, evidence for the effectiveness of these treatment booster sessions remains inconclusive. This study therefore evaluated the long-term effectiveness of relapse prevention treatment booster sessions for major depression.

Method: In a two-arm, parallel-group, maintenance-phase randomized controlled trial (RCT) with repeated longitudinal measures, the sample consisted of participants in Sweden who had received acute treatment for depression (internet-based behavioral activation or physical activity) and were then randomly assigned to either an 8-week relapse prevention program (n = 119) or control group (n = 143). Participants were followed-up for 24-months with both monthly self-report questionnaires (Patient Health Questionnaire 9-item & Generalized Anxiety Disorder 7-item) and quarterly diagnostic interviews (Mini-International Neuropsychiatric Interview; MINI).

Results: Both the relapse prevention group and control group exhibited similar depression-free trends over the course of the study period, with over 95% of participants in each group maintaining remission at the 24-month follow-up. Furthermore, all pre-hypothesized predictors of relapse were non-significant in differentiating the two groups at 24-month follow-up.

Discussion: These findings raise the question of whether treatment booster sessions are uniformly advisable for all mild–moderate cases of depression. For instance, preferentially recommending treatment boosters for psychotherapy-naïve individuals with depression may yield greater effects compared to individuals with difficult-to-treat depression. Our findings indicate that the efficacy of behavioral activation and physical activity may be even greater than previously reported, a testament to the lasting effects of internet-based psychotherapy.

Clinical trail registration: ClinicalTrials.gov, identifier NCT01619930.