The efficacy of a clustered group-based acceptance and commitment therapy for patients with chronic pain - a randomized controlled semi-crossover trial.

Purpose: The efficacy of Acceptance and Commitment Therapy (ACT) for chronic pain when provided as weekly sessions, is well documented. In scarcely populated areas, the traveling distance may be a barrier to weekly attendance. This study aimed to test the efficacy of a group-based ACT intervention, clustered into three bouts of three consecutive days, separated by 4 weeks.

Patients and methods: A total of 122 patients, recruited from a university hospital pain clinic, were randomized to either a clustered ACT or Treatment As Usual (TAU) provided by the primary health care services. The study had a semi-crossover design. Group effects of ACT versus TAU were assessed 3 months after the start of ACT by using linear mixed models for repeated measures. Outcome measures included pain intensity, health-related quality of life, pain acceptance, catastrophizing, and psychological distress.

Results: A total of 81 patients completed the ACT intervention. No statistically significant effects were observed on the primary outcome variables, pain intensity and health-related quality of life.

Significant group differences in favor of ACT were detected in pain acceptance (modified Cohen`s d = 0.32), including pain willingness (modified Cohen`s d = 0.30) and activity engagement (modified Cohen`s d = 0.23). The treatment effect remained at the 6- and 12-month follow-ups with a trend toward improvement.

Conclusion: A group-based ACT for chronic pain clustered into 3-day bouts may strengthen pain acceptance processes, including pain willingness and activity engagement. Reasons why the intervention did not affect pain intensity and health-related quality of life are discussed.