Acceptance and Commitment Therapy (ACT)

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1. What Acceptance and Commitment Therapy Is

Acceptance and Commitment Therapy (ACT) is not a substance but a psychotherapeutic approach. In its delivery the approach is only loosely standardised. The evaluated works describe sessions in individual and group settings, guided self-help programmes via the internet, telemedical sessions, bite-sized learning units and combinations with exercise programmes. Part of the literature tests the approach within interdisciplinary pain programmes, part of it in adolescents and their parents. The approach is therefore less a uniform protocol than a family of applications sharing a common goal.

For reading all works it is essential to understand how outcomes are measured in this field. ACT does not primarily alter a laboratory value but experience; the target variables are therefore predominantly questionnaires, for example on psychological flexibility, acceptance, pain intensity or fatigue. A questionnaire score is a marker, not a disease course. Secondly, the comparator condition is rarely the same: some studies compare with a wait-list group, others with another psychotherapy, and still others test two forms of the same approach against each other. The frequently cited 2017 telehealth study is explicitly designed as a non-inferiority trial; such a design cannot, by construction, demonstrate superiority. Thirdly, the approach and accompanying measures are often changed together, for example ACT together with an exercise programme and digital outcome tracking. From such combination studies the effect of ACT alone cannot be derived.

2. What the Studies Show in Detail

The supporting human studies and the most important reviews — by application area, with population, duration, preparation, measure and result as reported in the original works. Numbers appear only where the work states them.

Distribution of controlled human studies by application area — the numbers are not additive because one work may be assigned to several areas:

Cognition and Psyche

Proven The most reliable statements come from review articles. A 2023 meta-analysis pooled 21 randomised controlled trials with 1,962 participants and found standardised mean differences of 0.67 (95 % CI: 0.48, 0.87) for pain acceptance, 0.43 (95 % CI: 0.29, 0.57) for quality of life, −0.88 (95 % CI: −1.14, −0.63) for pain-related functional ability, −0.45 (95 % CI: −0.62, −0.27) for pain intensity, −0.35 (95 % CI: −0.54, −0.15) for anxiety and −0.74 (95 % CI: −0.98, −0.50) for depression 1. A second meta-analysis the same year across 33 studies with 2,293 participants reported small to moderate effects for pain intensity (g = 0.44) and physical function (g = 0.59) at treatment end and g = 0.34 and g = 0.56 at follow-up; for psychological endpoints the effects at treatment end were g = 0.43 (depression), g = 0.43 (anxiety) and g = 0.45 (quality of life) 2. A trial-sequential analysis indicated that the pooled estimates were not due to chance. Personally delivered ACT achieved larger effects on physical endpoints than internet-delivered ACT, and people with chronic headache and fibromyalgia benefited more than those with non-specific or mixed pain 2.

An earlier meta-analysis of 25 randomised controlled trials with 1,285 patients with chronic pain compared acceptance- and mindfulness-based approaches with wait-list, treatment as usual and education or support controls; effect sizes at treatment end ranged from small (on all endpoints except anxiety and pain interference) to moderate (anxiety and pain interference) 19. A 2022 overview of 25 randomised controlled trials of new-generation psychological treatments reported small to large effects in favour of ACT for pain interference, disability, depression and quality of life; three studies supported cost-effectiveness, and psychological flexibility emerged as a mediating process 23. An older meta-analysis of eleven studies found medium to large effects for pain acceptance and psychological flexibility, small to medium for functional ability, anxiety and depression, while pain intensity and quality of life did not differ significantly from zero 34.

Internet-mediated formats have been examined in several randomised studies. A study with 76 patients compared seven weeks of guided online ACT with a moderated discussion forum; the intent-to-treat analyses showed increases in activity engagement and pain willingness as well as reductions in pain-related distress, anxiety and depressive symptoms, which persisted after six months 21. A microlearning format with daily exercises (n = 57) versus waiting list (n = 56) improved pain interference, depression, anxiety, pain intensity, insomnia as well as psychological inflexibility and value orientation 29.

In-person and telemedical formats were compared directly. A randomised non-inferiority study with 128 veterans with chronic pain compared an eight-week ACT delivered via videoconference with in-person delivery; both groups improved on primary and secondary endpoints with the exception of sleep quality, non-inferiority was supported for the primary endpoint and several secondary endpoints, and activity at the six-month follow-up had increased more strongly in the in-person group; at the same time more participants in the video group discontinued treatment 22. An observational cohort of 252 patients (73.8 % female) in a four-week interdisciplinary programme in London showed significant improvements in insomnia severity (d = 0.45) and sleep interference 25. A non-randomised study with 164 adolescents (mean age 15.5 years) and one accompanying parent each over three weeks found improvements in depressive symptoms and psychological flexibility 28. In nursing homes 101 individuals (mean age 82.26 years) were randomised to ACT combined with compensation strategies or minimal support; significant time-by-intervention effects appeared for acceptance, pain-related anxiety, compensation strategies and pain interference while walking 31.

Some works address process measures and reviews. The Engaged Living Scale was examined in a non-clinical sample (N = 439) and a pain sample (N = 238) and showed good internal consistency as well as incremental validity for anxiety, depression, positive mental health and pain interference beyond acceptance and mindfulness 37. A review presents the psychological flexibility model as an integrative framework 38, a narrative review summarises the state of ACT for chronic pain and names three published systematic reviews with meta-analyses 39. A review on tinnitus classifies ACT as one of several psychological approaches 41. A feasibility study with 41 versus 41 participants examined a physically and mentally active programme with and without a digital measuring device 24. It remains open which patient groups benefit most from which format; the examination of moderators and predictors was limited and inconsistent 23.

Oncology

For people with lung cancer a feasibility study with 101 participants at a tertiary hospital in Sichuan examined a seven-week web-based ACT against usual care. The dropout rate was 13.86 %, the median implementation rate 71.43 % and satisfaction 65.9 %. Compared with the control group significant improvements appeared in quality of life (MD = 15.10; 95 % CI: 10.09, 20.11; d = 0.37), psychological flexibility (MD = −8.42; 95 % CI: −10.81, −6.03; d = −1.47) and anxiety (MD = −1.27; 95 % CI: −2.50, −0.05; d = −0.44) 27.

In adolescents and young adults with neurofibromatosis type 1 and chronic pain a pilot study examined a two-day ACT workshop in small groups with a telephone booster after one month. Ten adolescents (four male; mean age 16.9 years) and seven parents provided baseline and three-month data; satisfaction was moderate to high (3.9 in patients, 4.6 in parents on a scale of 1 to 5). Pain interference in the adolescents decreased significantly after three months, as did pain intensity reported by the adolescents 30.

A 2020 Cochrane review of psychological therapies for chronic pain in adults compared cognitive behavioural therapy, behaviour therapy and ACT with active controls or treatment as usual; studies on headache or malignant disease were excluded, and only studies with at least 20 participants per arm at treatment end were included 20. For oncological populations only individual feasibility and pilot studies are available so far; larger confirmatory studies with longer follow-up are still outstanding.

Fatigue and Stress

For burnout prevention in working people a systematic review pooled 14 quantitative works, all of which were controlled studies and used ACT in different formats in health, social and public services. The samples were small and the interventions not always clearly defined 43.

A feasibility study in the United Kingdom randomised 63 of 139 screened individuals with complex chronic pain (recruitment rate 45 %) to online ACT plus specialised medical pain treatment or specialised treatment alone. 56 % of online ACT participants rated themselves as “much improved” or better on a global change scale, versus 20 % in the control group; the three-month effects favouring online ACT were small for functioning and medication 26. The review on burnout calls for larger studies with explicit protocols and process measures; for employees with chronic pain a confirmatory study is still outstanding.

Further Investigations

A 2021 systematic review examined ACT for functioning in chronic pain and included twelve randomised controlled trials. Ten were rated “low risk” and two as “some concerns” with the revised Cochrane risk-of-bias tool. According to GRADE low to moderate evidence emerged for a positive immediate effect on functioning; whether the effect persists was inconsistent 32.

A 2021 review of online ACT for chronic pain evaluated 20 articles on 14 interventions. In ten articles the intervention was delivered via a dedicated website, in three cases additionally via an app; in most studies (n = 19) guidance was provided. The eight included randomised controlled trials reported online ACT as effective; information on implementation and design rationale was limited 42.

Two reviews place ACT within overarching models. One work describes psychosocial factors such as negative affect, childhood trauma, social support as well as pain-related catastrophising, self-efficacy and coping as influential variables on the course and treatment outcome of chronic pain 33. A 2024 review presents psychological flexibility with openness, awareness and engagement as a framework model and names chronic pain as one of the best-studied application fields 40. The review on functioning calls for more randomised controlled trials for specific pain conditions 32.

Bones and Joints

For older people with chronic pain a 2022 review compiles preclinical and clinical findings on mechanisms and perspectives. The most frequent pain complaints concern neurodegenerative and musculoskeletal diseases, peripheral vascular diseases, arthritis and osteoarthritis and are associated with low quality of life, social isolation, limited physical activity and dependence in daily activities. A changed pain experience with alterations in pain processing that may be linked to degeneration of the descending inhibitory pain pathways is proposed; in addition an increased pain threshold, a decline in painful sensations and reduced pain tolerance are described. Older patients with chronic pain have an elevated risk for dementia and cognitive impairment 35. This work addresses pain mechanisms in old age and not ACT itself; an examination of ACT specifically in older people with joint diseases is still outstanding.

Overall Picture

Proven Across fields the meta-analyses carry the strongest statements. ACT shows small to medium effects on pain intensity, functioning, depression, anxiety and quality of life in chronic pain, with the largest effects on pain acceptance and psychological flexibility 1234. The effects are usually smaller at follow-up than at treatment end 234. Internet-mediated formats achieve similar results to in-person formats, although in-person delivery was superior for physical endpoints 222. Psychological flexibility emerges as a mediating process in several works 2336.

Research begins where ACT has been examined in oncological populations, in employees with burnout and in young people with chronic pain: individual feasibility, pilot and review works are available 273043. A broader review addresses chronic pain in older people 35. The question of which patient groups benefit most from which format and duration has also not yet been clarified; the examination of moderators and predictors was limited and inconsistent 23. For specific pain conditions more randomised controlled trials are called for 32.

3. How Robust the Research Is

Controlled human studies are distributed very unevenly. Two areas stand out clearly: cognition and fatigue; followed by safety and oncology. The musculoskeletal system and the gut are represented by smaller groups, metabolism, inflammation, cardiovascular system and immune system by individual studies. The field is therefore primarily one of pain, stress and fatigue research. In the citation ranking, an observational study on psychosocial processes in chronic pain ranks highest; among the five most cited works, three are observational or basic research studies and two are reviews of controlled studies. Proven: For chronic pain, ACT appears multiple times in systematic reviews and meta-analyses.

Methodologically the field is broadly positioned. Randomised trials and the reviews that pool them are available multiple times for chronic pain. It is also characteristic that feasibility is explicitly reported: several studies are designated in the title as feasibility, proof-of-concept or pilot study. This is a sound approach, as it records what is feasible before the efficacy question is posed. The weakness lies in comparability. Formats, comparison conditions, durations and outcome measures differ considerably, and many target variables are self-reports. For areas outside pain and fatigue, individual controlled studies do not yet support any conclusion.

4. What Is Frequently Claimed — and What the Data Support

5. The Most Robust Studies

Ordered by strength of evidence, not by prominence: systematic reviews and studies with many participants first. The complete evaluation comprises considerably more studies; the most robust are listed here.

Controlled Human Studies

• 1 The Efficacy of Acceptance and Commitment Therapy for Chronic Pain: A Systematic Review and Meta-analysis (2023) — Review, 1.962 participants
• 2 The efficacy of acceptance and commitment therapy for chronic pain: A three-level meta-analysis and a trial sequential analysis of randomized … (2023) — Review, 2.293 participants
• 3 Acceptance and commitment therapy reduces psychological distress in patients with cancer: a systematic review and meta-analysis of randomized … (2023) — Review, 711 participants
• 4 Acceptance and Commitment Therapy Among Informal Caregivers of People With Chronic Health Conditions: A Systematic Review and Meta-Analysis (2023) — Review, 2.010 participants
• 5 Effectiveness of acceptance and commitment therapy on psychological flexibility, fatigue, sleep disturbance, and quality of life of patients with … (2023) — Review, 1.643 participants
• 6 Effect of acceptance and commitment therapy for depressive disorders: a meta-analysis (2023) — Review, 962 participants
• 7 Effects of acceptance and commitment therapy on cognitive function: A systematic review (2023) — Review, 904 participants
• The efficacy of psychological treatments on body dysmorphic disorder: a meta-analysis and trial sequential analysis of randomized controlled trials (2024) — Review, 905 participants
• 8 Interventions Based on Acceptance and Commitment Therapy for Stress Reduction in Children and Adolescents: A Systematic Review and Meta-Analysis of … (2024) — Review, 976 participants
• Psychotherapy for problematic pornography use: A comprehensive meta-analysis (2025) — Review, 2.021 participants
• 9 Process of change and efficacy of acceptance and commitment therapy (ACT) for anxiety and depression symptoms in adolescents: A meta-analysis of … (2025) — Review, 2.860 participants
• 10 Effectiveness of acceptance and commitment therapy in people with type 2 diabetes mellitus: A systematic review and meta-analysis (2024) — Review, 712 participants
• 11 Effects of acceptance and commitment therapy on negative emotions, automatic thoughts and psychological flexibility for depression and its … (2025) — Review, 1.362 participants
• 12 Effect of acceptance and commitment therapy for adolescent depression: a meta-analysis (2025) — Review, 2.352 participants
• Non-invasive treatments improve patient outcomes in chronic tinnitus: a systematic review and network meta-analysis (2024) — Systematic review, 2.354 participants
• 13 Mindfulness- and acceptance-based programmes for obsessive-compulsive disorder: A systematic review and meta-analysis (2025) — Systematic review, 2.221 participants
• The effectiveness of cognitive behavioral therapy for smoking cessation: A systematic review and meta-analysis (2025) — Systematic review, 2.531 participants
• 14 The effectiveness of Acceptance and Commitment Therapy on parental stress in parents of special children: a meta-analysis (2025) — Systematic review, 700 participants
• 15 Acceptance and Commitment Therapy for the Parents of Children and Adolescents with Autism Spectrum Disorder: A Systematic Review and Meta-Analysis of … (2026) — Systematic review, 698 participants
• 16 Acceptance and Commitment Therapy for Psychosocial Outcomes in Children and Young People with Long-Term Physical Health Conditions: Systematic Review … (2026) — Systematic review, 777 participants
• 17 Acceptance and Commitment Therapy for Psychosocial Outcomes in Children and Young People with Long-Term Conditions: A Systematic Review of … (2025) — Systematic review, 777 participants
• Comparative effectiveness of interventions incorporating physical activity in individuals with comorbid low back pain and depressive symptoms: a … (2026) — Systematic review, 834 participants
• 18 A systematic review and meta-analysis of acceptance and commitment therapy for older adults (2026) — Systematic review, 1.166 participants
• Non-Invasive Brain Stimulation for Core Symptoms of Chronic Primary Pain: A Meta-Analysis of RCTs (2026) — Systematic review, 1.371 participants

6. Summary

A meta-analysis from 2023 of 21 randomised controlled trials with 1962 participants found effects for pain acceptance, quality of life, functional ability, pain intensity, anxiety and depression; a second of 33 studies with 2293 participants reported small to medium effects for pain intensity and physical function. A review from 2022 of 25 randomised controlled trials found small to large effects for pain interference, disability, depression and quality of life. For oncological populations, individual feasibility and pilot studies are available.

Plausible Psychological flexibility emerged in several studies as a mediating process, and internet-delivered as well as in-person formats improved comparable endpoints. Hypothesis: If the relationship to one’s own thoughts and feelings changes, this could explain why pain acceptance and functional ability move together, while pain intensity responds less strongly. From combination studies in which ACT was tested together with an exercise programme and digital progress measurement, the effect of ACT alone cannot be derived.

A confirmatory study would need to clarify whether the effects persist beyond follow-up and which patient groups benefit most from which format. The review on functional ability calls for more randomised controlled trials for specific pain conditions; for employees with chronic pain and for oncological populations, larger studies with longer follow-up are still outstanding. Likewise, an examination of ACT specifically in older people with joint diseases is still outstanding. The review on burnout calls for larger studies with explicit protocols and process measures.

7. What Remains Open

• Mechanism: Can it be shown that ACT changes psychological flexibility more than an active comparator treatment, and does this change explain the further course?
• Format question: To what extent do pure internet and telehealth formats carry when tested against the same waiting-list condition as in-person formats?
• Scope: For which of the areas examined outside pain and exhaustion is a separate randomised examination worthwhile, and with which target measure?