Online Acceptance and Commitment Therapy (ACT) interventions use websites and smartphone apps to deliver ACT exercises and skills. The present meta-analysis provides a comprehensive review of online ACT self-help interventions, characterizing the programs that have been studied (e.g. platform, length, content) and analyzing their efficacy. A transdiagnostic approach was taken, including studies that addressed a range of targeted problems and populations. Multi-level meta-analyses were used to nest multiple measures of a single construct within their respective studies. A total of 53 randomized controlled trials were included (n = 10,730). Online ACT produced significantly greater outcomes than waitlist controls at post-treatment for anxiety, depression, quality of life, psychological flexibility, and all assessed outcomes (i.e. omnibus effect), which were generally maintained at follow-up. However, only psychological flexibility and all assessed outcomes at post-treatment were found to be significantly greater for online ACT when compared to active controls, with no significant follow-up effects. Overall, these results further clarify that ACT can be effectively delivered in an online format to target a wide range of mental health concerns, although it is less clear if and when online ACT is more efficacious than other online interventions.

Adherence challenges are common among digital mental health interventions (DMHIs). Single-session DMHIs may help by providing a low-intensity intervention that takes less time to complete. This pilot randomized controlled trial sought to evaluate the acceptability and preliminary efficacy of a single-session DMHI based on acceptance and commitment therapy (ACT) in a non-clinical sample of college students. The trial was pre-registered (NCT06139718). A total of 61 students were recruited, which was below the target of 100 participants. The participants were randomized to the single-session ACT DMHI or to a waitlist condition, with assessments completed at 1-week and 1-month follow-ups. The vast majority of participants (87%) completed the single-session ACT program. The participants provided high program satisfaction ratings. There were no differences between conditions on psychological flexibility, distress, or mental health help seeking. However, the participants assigned to ACT improved significantly more than the waitlist on well-being from baseline to 1-month follow-up (d = 0.29). Overall, the results were mixed, with some support for the acceptability and potential efficacy of a single-session ACT DMHI but also a lack of effect, most notably on psychological flexibility as the process of change in ACT.