Decision-Making Performance and Block-Wise Trajectories in Gambling Disorder and Opioid Use Disorder Using the Iowa Gambling Task

Background/Objectives: Decision-making differences have been reported in substance-related and behavioral addictions, but Iowa Gambling Task (IGT) performance patterns may differ. We compared IGT performance in gambling disorder, opioid use disorder (OUD) before and approximately 90 min after methadone dosing, and healthy controls. Methods: The study enrolled 103 adult men: 33 with gambling disorder, 30 with opioid use disorder (OUD) receiving methadone maintenance, and 40 healthy controls. One control participant discontinued the IGT before completion, leaving 39 complete control outcome records. Between-cohort inference therefore used 39 controls, 33 participants with gambling disorder, and 30 OUD pre-methadone observations; pre-/post-dose inference used 27 complete OUD pairs as repeated measurements. Results: Net Total differed across the three independent baseline cohorts, F(2,99) = 8.73, p < 0.001, and η2 = 0.150. Controls had higher scores than the gambling-disorder cohort (Holm-adjusted p = 0.032) and the OUD pre-methadone cohort (p < 0.001); gambling disorder versus OUD pre-methadone was not significant (p = 0.083). In OUD, the within-subject condition effect was not significant, F(1,26) = 1.55, p = 0.224. Block-wise profiles are presented descriptively; gambling disorder showed a 2.79-point Block 3-to-4 decrease. Conclusions: The recruited male gambling-disorder and OUD baseline cohorts showed lower mean IGT performance than healthy controls. Block-wise trajectories differed descriptively; the late decline in gambling disorder is exploratory and requires replication with prespecified contrasts or mixed-effects models.