Targeting excessive worry with internet-based extinction therapy: a randomised controlled trial with mediation analysis and economical evaluation.

BACKGROUND: Excessive worry is a common phenomenon. Our research group has previously developed an online intervention for excessive worry based on operant principles of extinction (IbET; internet-based extinction therapy) and tested it against a waiting-list. The aim of this study was to evaluate IbET against an active control comparator (CTRL). METHODS: A 10-week parallel participant blind randomised controlled trial with health-economical evaluation and mediation analyses. Participants (N = 311) were randomised (ratio 4.5:4.5:1) to IbET, to CTRL (an internet-based stress-management training program) or to waiting-list. The nation-wide trial included self-referred adults with excessive worry. The primary outcome was change in worry assessed with the Penn State Worry Questionnaire from baseline to 10 weeks. RESULTS: IbET had greater reductions in worry compared to CTRL [-3.6 point difference, (95% CI -2.4 to -4.9)] and also a significantly larger degree of treatment responders [63% v. 51%; risk ratio = 1.24 (95% CI 1.01-1.53)]. Both IbET and CTRL made large reductions in worry compared to waiting-list and effects were sustained up to 1 year. Treatment credibility, therapist attention, compliance and working alliance were equal between IbET and CTRL. Data attrition was 4% at the primary endpoint. The effects of IbET were mediated by the hypothesized causal mechanism (reduced thought suppression) but not by competing mediators. Health-economical evaluation indicated that IbET had a 99% chance of being cost-effective compared to CTRL given societal willingness to pay of 1000euro. CONCLUSIONS: IbET is more effective than active comparator to treat excessive worry. Replication and extensions to real-world setting are warranted.