Cognitive behaviour therapy (CBT) is an effective treatment for depression but access is limited. One way of increasing access is to offer CBT via the Internet. In Study I, guided Internet-based CBT was found to have a large effect on depressive symptoms compared to taking part in an online discussion group. Approximately two hours were spent on guiding each patient and the large effect found differs from previous studies that showed smaller effects, probably due to lack of guidance. The intervention had no effect on the participants’ quality of life but significantly decreased their level of anxiety.

Internet-based versions of self-report measures can be more practical and efficient than paper versions. However, before implementation, evidence of psychometrical equivalence to the paper versions should be available. This was tested in Studies II and III for the Montgomery-Åsberg Depression Rating Scale – Self-rated (MADRS-S) and the Beck Depression Inventory – Second Edition (BDI-II). When the full scales were investigated, equivalent psychometric properties were found in the two versions of the MADRS-S and BDI-II. However, in the Internet-version of the BDI-II, a lower score was found for the question about suicidality and the difference was statistically significant. Although the difference was small, this indicates that suicidality might be underestimated when using the Internet-based BDI-II.

As the long-term prognosis after treatment for depression is poor, in Study IV we investigated the possibility of delivering CBT-based relapse prevention via the Internet. The results revealed that fewer participants in the intervention group experienced a relapse compared to the control group and that the time spent on guiding each participant was approximately 2.5 hours. A trend towards a higher remission rate was found in the CBT group at the six-month follow-up and a reduction of depressive symptoms was associated with a lowered risk of relapse. CBT-based relapse prevention via the Internet can potentially be made available to large numbers of patients, thus improving their prognosis.

The Internet increases the possibilities for health care providers in the management of depression.