The Effectiveness of Acceptance and Commitment Therapy on Psychological Flexibility and Distress Tolerance in Men with Substance Use Disorder under Methadone Maintenance Treatment

Introduction: Substance use disorder leads to various physical, psychological, and social consequences, including reduced cognitive flexibility and distress tolerance. This study aimed to examine the effectiveness of Acceptance and Commitment Therapy (ACT) on psychological flexibility and distress tolerance in men with substance use disorder undergoing methadone maintenance treatment.
Methods: This quasi-experimental study was conducted in 2025 in Neyshabur with an experimental group and a control group. The sample consisted of 30 men with substance use disorder undergoing methadone treatment, who were randomly assigned to the two groups. The intervention group received eight sessions of ACT. Data were collected using standardized instruments on psychological flexibility and distress tolerance at three time points (pretest, posttest, and follow up). The data were analyzed using repeated measures analysis of variance in SPSS software.
Results: The findings indicated that the effects of time, group, and the time × group interaction were significant for both psychological flexibility and distress tolerance (p < 0.001). Bonferroni post hoc tests showed significant differences between pre-test and post-test, as well as between pre-test and follow-up in the intervention group (p < 0.001), while the difference between post-test and follow-up was not significant (p > 0.05). Additionally, the differences between the two groups at post-test and follow-up were significant for both variables (p < 0.001).
Conclusion: The findings suggest that ACT, by producing sustained improvements in psychological flexibility and distress tolerance, can serve as an effective complementary intervention for enhancing psychological resilience in men undergoing methadone maintenance treatment.