Long-term dosage effects of psychodynamic and schema therapy in depressed patients with personality disorders: 18 and 24 months follow-up of a randomized controlled trial

Background Providing psychotherapy at 50 sessions in a year (starting twice weekly) led to faster and greater improvements in depression and personality functioning compared to 25 sessions, starting weekly for patients with depression and personality disorder (PD). This study reports long-term dosage effects at 18 and 24 months. Methods In a pragmatic, double-randomized clinical trial, 246 outpatients with depression and PD were assigned to (1) 25 or 50 sessions and (2) Short-term Psychodynamic Supportive Psychotherapy (SPSP) or Schema Therapy (ST). Depression severity was assessed with the Beck Depression Inventory-II. Secondary outcomes included diagnostic remission of depression (MINI-plus), PD (SCID-II/SCID-5-P), and treatment-specific measures. Intention-to-treat analyses were conducted. Results At 18 and 24 months, BDI-II means did not differ between dosage groups (19.0 for 25 sessions versus 19.1 for 50 sessions; d = -0.01; 95% CI = -0.35-0.37, p = 0.96). The lower-dosage group improved during follow-up (-2.6 BDI points, p = 0.031), which may be partly attributed to additional therapy received by a subgroup. Remission rates at 24 months were 66% for depression and 76% for PD, with no differences between conditions. Conclusions Higher psychotherapy dosage led to faster initial improvements, but long-term outcomes were not superior to those achieved with a lower dosage. These results should be interpreted with caution, as unregulated treatment during follow-up reduced the power to detect significant dosage effects. Both SPSP and ST provide viable alternatives to treatments focused solely on depression.