The study is a randomized controlled trial and to compare the benefits of a 10-week web-based unguided self-help treatment with the same intervention complemented with weekly therapist support via e-mail. A waiting-list control group will be included. The Beck Depression Inventory (BDI-II) will be used as the primary outcome measure. Secondary outcomes include general psychopathology, interpersonal problems, and quality of life.

Depression is a major health problem associated with significant disability and economic costs. Although depression can be treated effectively with several psychological and pharmacological treatment options, many sufferers still seek or receive inadequate therapy or no therapy at all. Internet-based treatments may help to serve this demand, being accessible anytime and anywhere making it easier for underserved populations and people living in remote areas to receive treatment. The present study aims to assess the efficacy of an internet-based CBT intervention for depression (Deprexis), directly comparing the benefits of a low intensity therapist-guided with an unguided self-help version. A waiting-list control group will be included. Individuals meeting the diagnostic criteria of major depression or dysthymia will be randomly assigned to one of the three conditions. While unguided self-help will not include any contact with a therapist or the study team during the treatment, guided self-help will include a weekly scheduled e-mail feedback by a therapist and the possibility to ask questions via e-mail. While in an earlier study Deprexis was assessed as an add-on to TAU, this study will examine the efficacy of the program when delivered as a stand-alone intervention (i.e., only individuals who currently do not receive psychotherapy will be included). Moreover, this study will include a structured diagnostic interview at pretreatment. Only participants fulfilling the criteria of a depressive disorder (major depression or dysthymia) will be included in the trial. Participants will be recruited in Switzerland and Germany via articles in national and regional newspapers and a national television interview. All questionnaires will be administered via the internet. The 21-item BDI-II will be used as the main outcome measure. Secondary outcome measures will include the Brief Symptom Inventory (53-item BSI), the Inventory of Interpersonal Problems (64-item IIP), and the WHOQOL-BREF.

Inclusion Criteria:

• access to the internet
• informed consent to participate
• BDI-II score > 13
• if prescribed, constant dosage of medication (depression/anxiety) for 1 month prior and during study

Exclusion Criteria:

• suicide item of BDI ≥ 2
• other psychological treatment during this study

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