Psychiatry · Medical Literature
Do Acceptance- and Mindfulness-Based Interventions Improve Psychological Flexibility in People With Chronic Pain? A Systematic Review and Meta-Analysis of Randomized Controlled Trials.
Abstract
Acceptance- and mindfulness-based interventions are effective for improving pain-related outcomes, yet their effects on psychological flexibility have not been meta-analyzed. This systematic review and meta-analysis addressed this gap by comparing these interventions with control conditions on psychological flexibility and its core dimensions in adults with chronic pain. Searches were conducted in PsycINFO, MEDLINE, Cochrane CENTRAL, Scopus and Web of Science from inception to May 2025. Sixty randomized controlled trials comprising 6692 participants were included. Meta-analyses were conducted for global psychological flexibility (k = 17), acceptance (k = 38), committed action (k = 4) and values (k = 4). Heterogeneity, risk of bias and certainty of evidence were assessed. Interventions significantly improved psychological flexibility at post-treatment, short-term (≤ 6 months) and long-term (> 6 months) follow-up (g = 0.35-0.69), and acceptance across all time points (g = 0.41-0.77). Effects for committed action and values were non-significant. Heterogeneity was substantial, most trials had a high risk of bias, and the certainty of evidence was low to very low. Moderator analyses indicated larger effects when interventions were compared with inactive controls, delivered by psychologists or implemented as stand-alone programs. Evidence suggests that acceptance- and mindfulness-based interventions may improve global psychological flexibility and acceptance. However, the certainty of evidence was low to very low, and most included trials were at high risk of bias. More rigorous trials are needed to clarify effects across specific dimensions of psychological flexibility. This systematic review and meta-analysis provide the first comprehensive synthesis of the effects of acceptance- and mindfulness-based interventions on psychological flexibility in chronic pain. These findings show that these interventions improve psychological flexibility, particularly pain acceptance, supporting it as a clinically relevant treatment target. PROSPERO: CRD420251018441.
Clinical relevance
In adults with chronic pain, do acceptance- and mindfulness-based interventions (AMBIs) improve psychological flexibility and its core dimensions—acceptance, committed action, and values—compared to control conditions across post-treatment and follow-up time points? __SNAPSHOT__ {"studyDesign":"Systematic review with meta-analysis of randomized controlled trials (RCTs)","setting":"International; searches conducted across PsycINFO, MEDLINE, Cochrane CENTRAL, Scopus, and Web of Science from inception to May 2025","sampleSize":"60 RCTs comprising 6,692 participants; meta-analyses conducted for global psychological flexibility (k=17), acceptance (k=38), committed action (k=4), and values (k=4)","population":"Adults with chronic pain (specific pain diagnoses, comorbidities, pain duration, and demographic characteristics not further specified in the available abstract)","intervention":"Acceptance- and mindfulness-based interventions (AMBIs; e.g., Acceptance and Commitment Therapy [ACT], Mindfulness-Based Stress Reduction [MBSR], Mindfulness-Based Cognitive Therapy [MBCT], and related approaches)","comparator":"Control conditions (specific types—e.g., waitlist, treatment-as-usual, active control—not further specified in the available abstract)","primaryOutcome":"Psychological flexibility (global construct) and its core dimensions: acceptance, committed action, and values, assessed at post-treatment, short-term follow-up (≤6 months), and long-term follow-up (>6 months)","followUp":"Post-treatment, short-term (≤6 months), and long-term (>6 months); specific maximum follow-up duration not reported in the available abstract","fundingSource":"Not reported in the available abstract"}
Key findings
AMBIs produced statistically significant improvements in global psychological flexibility at post-treatment, short-term follow-up (≤6 months), and long-term follow-up (>6 months), with pooled Hedges' g ranging from 0.35 to 0.69 across these time points (direction of effect favors intervention; p-values, confidence intervals, and NNT not reported in the available abstract). These effect sizes are conventionally characterized as small-to-medium. Acceptance—the most extensively meta-analyzed subdimension (k=38)—similarly demonstrated statistically significant improvement across all three time points, with Hedges' g ranging from 0.41 to 0.77, representing small-to-medium to medium effects. In contrast, effects on committed action (k=4) and values (k=4) were non-significant; however, the very small number of trials contributing to these subdimension analyses (k=4 each) severely limits interpretability. Heterogeneity is described as 'substantial' in the abstract (specific I² values not reported in the available excerpt). Risk of bias and certainty of evidence were formally assessed (specific ratings and GRADE classifications not available in the provided abstract). No adverse event data were reported.
Practice implications
This meta-analysis provides the first pooled evidence that AMBIs—principally ACT and mindfulness-based approaches—reliably improve global psychological flexibility and pain acceptance in adults with chronic pain, with effects that are maintained at both short-term and long-term follow-up. The consistency of the acceptance findings across a large number of trials (k=38) strengthens confidence in that specific subdimension. However, the analysis did not establish treatment effects on committed action or values, two theoretically central ACT processes; this may reflect genuine null effects, insufficient measurement power due to very few contributing trials (k=4 each), heterogeneity in how these constructs are operationalized, or publication/reporting bias toward acceptance outcomes. The effect sizes for global flexibility (g=0.35–0.69) are statistically significant but modest in magnitude; their clinical meaningfulness—in terms of impact on function, quality of life, or pain-related disability—cannot be determined from this abstract alone, as those outcomes were not the focus of this analysis. Generalizability is uncertain: the specific chronic pain diagnoses, demographic composition, intervention formats (face-to-face vs. digital, individual vs. group), dose, and comparator types across included trials are not delineated in the available abstract. The finding that only two of four theorized flexibility dimensions showed significant treatment effects introduces important uncertainty about the theoretical model of change. Clinicians should interpret these results as informative regarding process-level outcomes (particularly acceptance) rather than as a mandate to select AMBIs primarily on the basis of flexibility gains. Importantly, only the abstract was available for this review; full inspection of heterogeneity statistics, GRADE ratings, and moderator analyses is necessary before drawing firm practice conclusions. __LIMITATIONS__ Substantial heterogeneity across included trials was explicitly noted, though I² values and potential sources (intervention type, comparator, pain diagnosis, delivery format) are not specified in the available abstract, limiting interpretation of pooled estimates.,The committed action and values subdimension analyses rested on only k=4 trials each, providing severely underpowered estimates and precluding meaningful conclusions about these theoretically important ACT processes.,Blinding of participants and therapists is inherently not feasible in psychotherapy RCTs, introducing performance and detection bias risk across included studies.,Certainty of evidence ratings (e.g., GRADE) were performed but are not reported in the abstract, preventing assessment of the overall evidentiary confidence.,The nature of control conditions across 60 included trials is unspecified (waitlist vs. active vs. treatment-as-usual), and effect sizes are likely to differ substantially by comparator type—an important moderator not addressed in the available data.,The abstract does not report confidence intervals or p-values for individual meta-analyses, preventing independent appraisal of the precision of pooled estimates.,Specific chronic pain diagnoses are not delineated, limiting generalizability to particular clinical populations (e.g., fibromyalgia, neuropathic pain, low back pain).,Psychological flexibility and its subdimensions are process/mechanism outcomes, not patient-centered clinical outcomes (e.g., pain intensity, disability, quality of life); the relationship between flexibility gains and meaningful functional improvement is not established in this meta-analysis.,Potential publication bias favoring positive findings—particularly for acceptance, the most commonly measured dimension—was assessed but results are not reported in the abstract.,Only the abstract was available for this review; full methodological details, subgroup analyses, and sensitivity analyses required for complete appraisal are not accessible. __BOTTOM_LINE_CATEGORY__ potentially_practice_informing __BOTTOM_LINE__ Acceptance- and mindfulness-based interventions produce small-to-medium improvements in global psychological flexibility and pain acceptance in adults with chronic pain, with effects persisting through long-term follow-up (>6 months); these findings support the theoretical mechanism of change underlying ACT and MBSR/MBCT. Effects on committed action and values were non-significant, though each rested on only four trials, and substantial heterogeneity limits the precision of all pooled estimates. Clinicians may reasonably use these findings to reinforce that acceptance-focused techniques represent an evidence-supported therapeutic process in chronic pain management, while recognizing that process-level gains in flexibility do not yet confirm superiority over other active treatments on patient-centered functional outcomes.