Internet-based CBT for patients with depressive disorders in primary and psychiatric care: Is it effective and does comorbidity affect outcome?

Internet-based cognitive behavior therapy (ICBT) has proved effective in reducing mild to moderate depressive symptoms. However, only a few studies have been conducted in a regular healthcare setting which limits the generalizability of the results. The influence of psychiatric comorbidity on outcome is not well understood. In the current study, patients with mild to moderate depressive symptoms in primary and psychiatric care were interviewed using the SCID-I and SCID-II to assess psychiatric diagnoses. Those included were randomly allocated to ICBT (n = 48) or to an active control condition (n = 47). Both groups received therapist support. At post-treatment, ICBT had reduced depressive symptoms on the BDI-II more than the active control intervention (p = .021). However, the difference between groups was no longer significant at the 6-, 12- or 24-month follow-ups. The within-group effect size after ICBT (BDI-II) was large (d = 1.4). A comorbid anxiety disorder didn't moderate the outcome, while the presence of a personality disorder predicted significantly less improvement in depressive symptoms. ICBT had a large effect on depressive symptoms in a sample from regular healthcare. It is possible to obtain a large effect from ICBT despite comorbid anxiety, however, including patients with a comorbid personality disorder in the current form of ICBT seems questionable.