Effects of group Acceptance and Commitment Therapy (ACT) on anxiety and depressive symptoms in adults: A meta-analysis

Background: A comprehensive meta-analysis quantitatively examining the effects of group Acceptance and Commitment Therapy (ACT) on anxiety and depressive symptoms is required to advance our understanding of its efficacy and moderating factors. Methods: Four electronic databases were searched in August 2018. An update search was conducted in November 2021. Forty-eight randomised controlled trials (RCTs) were included in this review (3292 participants: anxiety = 34 RCTs, depression = 40 RCTs). Results: The overall effect size for anxiety symptoms was medium-to-large (g = 0.52, p < 0.001; 95% CI = 0.30–0.73), while the overall effect size was small-to-medium for depressive symptoms (g = 0.47, p < 0.001; 95% CI = 0.31–0.64). Subgroup analyses demonstrated that group ACT was significantly superior to non-active controls (e.g., waiting list) in reducing anxiety and depressive symptoms. Group ACT was only significantly superior to active controls (e.g., CBT) in reducing depressive symptoms. Subgroup analyses also demonstrated that the effect size can vary depending on the number of sessions provided and the primary condition of participants recruited. Limitations: The number of studies included in each category of subgroup analyses was small and the risk of bias varied across studies. There was high heterogeneity among the included studies, and this might have affected the results. Conclusion: The current evidence suggests that group ACT may be effective in treating anxiety and depressive symptoms, perhaps more so for depressive symptoms when compared to other well-established treatments. The intensity of treatment and the targeted population may need to be considered when delivering group ACT.