The aim of the study is the examination of effectiveness and cost-effectiveness of a telephone-based psychotherapy (Tel-PT) for depression compared to treatment as usual in primary care.

The overall purpose of the study is to examine the effectiveness of telephone psychotherapy (Tel-PT) for the treatment of mild to moderate depression on different outcome-levels and under clinically representative conditions in Swiss primary health care. The randomized-controlled trial (RCT) will evaluate the primary hypothesis that Tel-PT is more effective than routine primary care (i.e. treatment as usual, TAU), more specifically, that it leads to significant higher reduction in depression severity than TAU at follow-up.

The intervention group (IG) receives a manualized short-term cognitive behavioral treatment, which is the adapted German version of the program "Creating a balance" developed in the USA. The therapy consists of one face-to-face and 8-12 telephone contacts and is carried out by a licensed psychotherapist.

More concrete, recruitment and inclusion of the patients will be carried out by the participating general practitioners (GPs). GPs will be instructed to screen patients at risk for depression, especially those revealing diffuse somatic symptoms and suffering from chronic diseases. If positively screened, patient's depressive symptoms are assessed with Patient Health Questionnaire (PHQ-9) and diagnosed according to ICD-10.

All GPs will receive an initial training prior to their participation, providing them with study information and procedures as well as training in screening procedure, psychodiagnostics and study enrolment.

Eligible patients are provided with detailed study information and asked to participate. Subsequently, patients will give informed consent. Patients will then be included into the study and fill out the baseline questionnaires (t0). After that, randomization will be carried out at the University of Zurich, based on an appropriately created computer algorithm. Both GPs and patients are informed about the results by the study team within two days. Subsequently, patients in control group (CG) will receive regular text messages and patients in the intervention group (IG) will be called by the study therapist to schedule an initial appointment.

In case of positive results, the overarching objective is the optimization of mental health services for depressed patients by implementing an evidence-based, accessible and cost-effective treatment option into primary care.

Inclusion Criteria:

• PHQ-9 score of > 5 and ≤15.
• Informed Consent as documented by signature (Appendix Informed Consent Form)
• Minimum age of 18 years
• Diagnosis of mild to moderate depression according to ICD-10 (F32.0, F32.1, F33.0, F33.1)

Exclusion Criteria:

• Patients currently being in psychotherapeutic treatment or treatment in past three months
• Suicidal tendencies or suicidality
• Insufficient knowledge of German language
• Health condition that does not allow questionnaire completion