Effects of group-based parent training on oppositional defiant disorder symptoms and irritability in Japanese children

Background Oppositional defiant disorder (ODD) is a childhood disorder associated with substantial functional impairment. Although parent training (PT) is the gold standard intervention for ODD, evidence from non-Western contexts is limited, and its effect on irritability—a core emotional dimension of ODD—remains unclear. Methods This open trial examined the effectiveness of a group-based parent training program for parents of children with ODD (PT-ODD). Twelve Japanese mothers who had children aged 7–12 years participated. Outcomes were assessed at pre-treatment, post-treatment, and three-month follow-up using clinician-rated and parent-reported measures. Changes over time were analyzed using linear mixed-effects models, and associations between parenting behaviors and child symptoms were examined. Results Clinician-rated functional impairment and parent-reported oppositional defiant symptoms showed significant and sustained improvements, with large effect sizes. Remission rates increased from 33% post-treatment to 50% at follow-up. Irritability showed no immediate improvement and the overall time effect did not reach statistical significance. However, irritability was significantly lower at follow-up than at baseline, suggesting a potential delayed effect. Changes in positive parenting behaviors were associated with short-term improvements in oppositional defiant symptoms, whereas changes in negative parenting behaviors were observed for longer-term changes in oppositional defiant symptoms. Conclusions These findings suggest that PT-ODD leads to immediate improvements in ODD symptoms and functional impairment, whereas reductions in irritability may emerge more gradually over time.