Adult-diagnosed and childhood-diagnosed attention deficit/hyperactivity disorder: cognitive and environmental contributions to symptom severity across different age of diagnosis

Background Attention deficit/hyperactivity disorder (ADHD) is characterized as a neurodevelopmental disorder onset in childhood. However, accumulating evidence suggests that some adults may fulfill current diagnostic criteria for ADHD despite reporting no clinically significant symptoms during childhood. It remains unclear whether executive function and environmental factors relate differently to symptom severity across different age of diagnosis. Methods Seventy-two adults with ADHD were recruited and classified into childhood-diagnosed (N = 37) and adult-diagnosed (N = 35) groups using structured diagnostic interviews and retrospective symptom ratings. ADHD symptoms were assessed using the Adult ADHD self-report scale, executive function with the Behavior Rating Inventory of Executive Function-Adult Form, emotional symptoms via the Self-Rating Anxiety Scale and Self-Rating Depression Scale, and environmental factors using the Childhood Trauma Questionnaire, Connor-Davidson Resilience Scale, and Parental Bonding Instrument. Hierarchical multiple regression and moderation analyses were conducted to evaluate independent contributions and diagnosis-specific effects on ADHD core symptoms. Results There was no significant age difference between the adult-diagnosed and childhood-diagnosed ADHD groups (25.63 ± 4.89 vs. 26.32 ± 4.69 years). Compared to the childhood-diagnosed group, adults with adult-diagnosed ADHD showed lower childhood symptoms but similar adulthood severity, alongside superior self-monitoring and significantly more psychiatric comorbidities and emotional distress. Executive function was the strongest and most consistent predictor of both inattention ( β = 0.64, p < 0.001) and hyperactivity-impulsivity symptoms ( β = 0.47, p < 0.001), whereas environmental factors contributed minimal additional explanatory power, with a modest association between parental overprotection and inattention ( β = 0.28, p = 0.016). No diagnosis-specific moderation effects were observed (all p > 0.05). Conclusions These findings suggest that while adult-diagnosed ADHD presents with a complex clinical profile, executive function and environmental factors do not play a primary role specific to the age of diagnosis.