A total of 384 patients suffering from chronic depressive disorder will be randomized to receive treatment as usual, CBASP, or befriending for a period of five months. The primary outcome is change in Montgomery-Åsberg Depression Scale. Secondary outcomes include changes in self-reported psychiatric symptoms, biomarkers determined from venous blood samples, and neurophysiological parameters. The data gathering is performed at pre- and post intervention stages (i.e., at baseline and at five months). A follow-up questionnaire is sent to the participants six months after the intervention.