Effectiveness of cognitive behaviour therapy for treatment-resistant depression with psychiatric comorbidity: comparison of individual versus group CBT in an interdisciplinary rehabilitation setting.

Cognitive behaviour therapy (CBT) has been shown to be effective, yet there is a paucity of research on the differential effectiveness of individual and group CBT for adults with treatment-resistant depression with psychiatric comorbidity.
To investigate the effectiveness of individual and group CBT for inpatients, in an interdisciplinary rehabilitation setting; the extent of psychiatric comorbidity; and who benefits the most from group CBT.
All patients (n = 181) received 6 weeks of rehabilitation (treatment as usual, TAU). In addition, they were randomly allocated to group CBT (n = 86) or individual CBT (n = 59) combined with TAU, or TAU only (n = 36). All CBT therapists were part of an interdisciplinary team, had at least 1-year CBT training, and attended weekly supervision. The same CBT manual was used for individual and group therapy, providing 12 sessions, two per week. Groups had 12-15 participants and two therapists in each session.
Individual CBT was superior in efficacy to group CBT and TAU, with a large within-subject effect size (ES = 2.10). Group CBT was not superior to TAU. The benefits of treatment decreased over time, but remained large at 18-month follow-up for individual CBT (ES = 1.02), and medium for group CBT (ES = 0.46) and TAU (ES = 0.60).
Individual CBT was an effective addition to TAU and showed significant improvements in symptom severity post-treatment and at 18-month follow-up. Disorder severity and comorbidity may have decreased effectiveness of group therapy primarily aimed at depression.