Effects up to 20-Year Follow-Up of Preventive Cognitive Therapy in Adults Remitted from Recurrent Depression: The DELTA Study

Introduction: Major depressive disorder (MDD) is common, and recurrence rates are high. Preventive Cognitive Therapy (PCT), has been shown to prolong time to recurrence and reduce risk of recurrence(s) over 2-10 years in patients with recurrent depression. Objective: The aim of the study was to examine the effectiveness of PCT over 20 years on time to first recurrence, cumulative proportion of first recurrences, percentage of depression-free time, mean severity of recurrences, and the number of recurrences within a patient. Methods: Adults remitted from recurrent MDD were randomized to PCT or Treatment As Usual (TAU). Clinical outcomes were assessed using the SCID over 20 years. We used Cox regression analyses, Kaplan-Meier analyses, ANOVA, and negative binomial regression and tested for interaction with the number of previous episodes. Results: There was a significant interaction effect for number of previous episodes with treatment condition on time to first recurrence (Wald[1, n = 172] = 8.840, p = 0.003). For participants with more than 3 previous episodes, the mean time to recurrence was 4.8 years for PCT versus 1.6 years for TAU; the cumulative proportion of first recurrences was 87.5% for PCT and 100% for TAU. For participants with more than 3 previous episodes, exploratory analyses suggest that PCT had 53% less recurrences and percentage of depression-free time was significantly higher compared to TAU. There were no significant effects on mean severity. Conclusions: Up to 20 years, for MDD patients with more than 3 previous episodes, those who received PCT had significantly longer time to a first recurrence and lower recurrence risk and may have less recurrences and more depression-free time compared to TAU. This suggests long term protective effects of PCT up to 20-years.