Abstract
Objective: Internet-based cognitive behavioural therapy (iCBT) is an efficacious, scalable intervention that could help meet the significant demand for psychological treatment. Yet, there is limited real-world evidence for its effectiveness. This study investigated the use and effectiveness of a free iCBT programme ('Just a Thought') in New Zealand. Methods: We analysed 18 months of user data from the Just a Thought website to understand the characteristics of those who used the Depression and Generalised Anxiety Disorder courses, how many lessons they completed, how mental distress changed across each course and the factors associated with adherence and improvement in mental health. Results: The results for both courses followed very similar patterns. Course adherence was low overall. There were small differences in adherence by age, gender and ethnicity, and larger differences for those who were 'prescribed' Just a Thought by a healthcare worker. Mixed models showed significant reductions in mental distress, with some tapering of improvement across latter lessons. Those most likely to show clinically meaningful reductions in mental distress had completed more lessons, were older and had a higher baseline level of distress. Conclusion: Alongside previous efficacy research, this real-world data indicate that iCBT is most likely to be effective at the population level and across different subgroups if users complete as much of the course as possible. Strategies to increase course adherence and maximise the public health benefits of iCBT include healthcare workers 'prescribing' iCBT and tailored solutions to meet the needs of young people, Maori and Pasifika.