Primary insomnia (PI) is a highly prevalent health problem worldwide and has been identified as a risk factor for major somatic and mental disorders. Still, less than 50% of all individuals with chronic PI show full remission with optimized first line treatment, indicating the need for additional research. The broad objective of this study was to test acceptance and commitment therapy (ACT) as a supplement to first line treatment in order to improve non-pharmacological interventions for insomnia.

Specific aims were i) to evaluate whether ACT is feasible in patients with PI and ii) to collect preliminary efficacy data. Improvements of subjective sleep quality and quality of life (QoL) were hypothesized.

Eleven individuals with chronic PI without comorbidities who were non- or partial responders to Cognitive Behavior Therapy were included. They participated in six weekly ACT sessions in an outpatient group setting. Primary outcomes were subjective sleep quality as measured by sleep diary data, and quality of life as measured by the World Health Organization Quality of Life. Data were collected at two baselines, post-treatment and at three-months-follow-up.

Ten individuals completed the study. Sleep parameters did not significantly change across the study. Importantly, the QoL across different domains was significantly improved after ACT. Sleep-related avoidance behavior was significantly reduced. Effect sizes for QoL and avoidance behavior changes were large.

The data provide preliminary evidence that ACT as a group program is feasible in individuals with chronic PI and could be a helpful supplement to existing treatments especially with the aim of improving QoL.