Randomized controlled evidence of the efficacy of acceptance and commitment therapy: A systematic review and...

The comparative efficacy of acceptance and commitment therapy (ACT) relative to other bona fide psychotherapies has been obscured by methodological limitations and variability in how ACT and active comparators are operationalized. We therefore conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) comparing full-model ACT (therapist-delivered, multi-session interventions targeting the core ACT processes) to bona fide psychotherapies. We identified 34 RCTs meeting our inclusion criteria. In line with prior critiques of the ACT literature, we identified several common methodological shortcomings, such as lack of preregistration of primary outcomes and hypotheses, inadequate statistical power for detecting differential effects, limited use of intent-to-treat analyses, and interpretive overreach. Random-effects three-level meta-analyses indicated that full-model ACT was not superior to bona fide psychotherapies on mental and behavioral health outcomes (g = -0.01, p = .86). Secondary, hypothesis-generating post hoc analyses examined clinical significance, ACT-targeted processes, and an exploratory TOST comparison against a prespecified equivalence region (g = ±0.20). Current RCT evidence does not justify recommending full-model ACT over other established treatments. Further progress will require more rigorous comparative trials and idiographic designs that better align with the ACT model.