Internet-based self-help treatment for panic disorder: a randomized controlled trial comparing mandatory versus optional complementary psychological support.

Panic disorder (PD) is one of the most common psychiatric disorders. Web-based self-help treatments for PD have had promising results. These online treatments seem to have larger effect sizes (ESs) when professional support is added. However, the amount of support or how it should be administered is not yet clear. The aim of this trial was to study two ways of administering psychological support provided by phone as a part of Internet-based self-help treatment for PD based on cognitive behavioral therapy. Seventy-seven participants diagnosed with PD were randomly assigned to one of three experimental conditions: a waiting list control group; a treatment group with non-scheduled psychological support; or a treatment group with scheduled psychological support. PD symptoms of participants who received treatment improved significantly compared to the control group (mean ES d = 1.18, p < .05). In addition, there were statistically and clinically significant differences between treatment groups (Mean difference = -3.20, p = .005, 95% CI [-5.62, -.79]). The scheduled group showed a larger ES, a lower dropout rate, and better adherence to treatment than the non-scheduled group. Scheduled support seems to be indicated for patients who seek Web-based treatment for PD, and their symptoms of panic, anxiety, and depression improve at post-treatment and six-month follow-up. In contrast, when support depends on patient demand, they receive less support and so, the therapeutic effect is poorer.