Long-Term Effects of Positive Psychotherapy Compared to Cognitive Behavior Therapy in Clinical Depression: An 18-Month Follow-Up Randomized Controlled Trial

<b>Background/Objectives</b>: Positive Psychotherapy (PPT) is an empirically supported treatment that directly targets positive resources and personal strengths as its primary logic. PPT is effective in amplifying happiness and well-being as an additional way to enhance positive mental health while also ameliorating symptoms of negative affect, especially in depression, anxiety disorders, and stress disorders. However, few studies have been conducted to investigate these effects in the long run. This study extends our previously published findings on the short-term efficacy of PPT by extending the follow-up period to 18 months and comparing its long-term effects with those of Cognitive Behavioral Therapy (CBT) within the same randomized controlled trial. <b>Methods</b>: Forty-nine out-patient participants with a DSM-IV diagnosis for depressive disorder (MDD, Dysthymia) were treated with 14 sessions of manualized PPT (<i>n</i> = 23) or CBT (<i>n</i> = 26) group therapy. In a randomized controlled two-center-study, questionnaires on depressive symptoms (BDI-II, MADRS, DHS), psychological distress (BSI), and well-being related outcomes (FS, PPTI, SWLS) were administered at baseline and 18-month follow-up. <b>Results</b>: Analyses using linear mixed models indicated significant differences in long-term treatment outcome for depressive symptoms (BDI-II, DHS, MADRS) and satisfaction with life (SWLS), depicting better outcomes for the PPT group. Between group effect sizes at 18-month follow-up were primarily in the middle range for all outcome measures, in favor of PPT. <b>Conclusions</b>: This study provides support for the long-term efficacy of PPT in the treatment of depression and improvement of positive resources.