Psychosocial stress is a major public health concern, contributing to significant suffering and costs to society. There is a lack of effective interventions that could be offered at an early stage to people who need to reduce their stress in life. Recent advances in psychology have provided evidence-based exercises suitable for testing in an entirely digital intervention. This study aims to estimate the effectiveness of a 12-week digital course in mindfulness- and acceptance-based stress reduction.

The effectiveness of the 12-week digital course will be estimated in a parallel-groups randomised controlled trial, in which the control group will receive referrals to self-studies on mental health information found online. The study population will be individuals 15 or older, seeking help online for stress and who have access to a mobile phone. Employing a Bayesian sequential design, the primary outcome will be monitored monthly, after the 6-month follow-up, to calculate target criteria for when to stop recruiting. Perceived stress (Cohen’s 10-item version) will be the primary outcome, with estimands of interest being differences between groups at 3 (immediate), 6 (prolonged) and 12 months (maintained). Mediation analysis will reveal if differences between groups are mediated by acquired equanimity. Effectiveness will be analysed with Bayesian regression models, and mediation will be analysed by using a causal inference framework.

The research was approved by the Swedish Ethical Review Authority on 2024-05-07 (2024-01974-01). The study will reach out to a vulnerable population, and participation may displace efforts to seek professional help. We have built-in automatic advice to seek additional help for participants scoring high on the depression scale at baseline, before allocation to study groups. The findings from this study will be submitted to peer-reviewed journals and presented at relevant national and international meetings.

ISRCTN39222610.