Sex Differences in Adult ADHD: A Multidimensional Multi-Informant Observational Study.

Background/Objectives: Sex differences in adult attention-deficit/hyperactivity disorder (ADHD) remain insufficiently characterized, particularly in clinically referred samples assessed through multidimensional and multi-informant approaches. This study investigated sex differences in clinical presentation, psychiatric comorbidity, psychometric features, and ADHD severity in adults with ADHD, with a specific focus on emotional dysregulation and rating-source effects. Methods: A total of 212 consecutively recruited adults with ADHD, including 93 females and 119 males, underwent a comprehensive assessment at a tertiary referral service. Sex differences were examined across sociodemographic, clinical, comorbidity, functional, and psychometric domains. ADHD severity was assessed using both self-rated and observer-rated measures. Regression, mediation, and repeated-measures mixed-effects models were fitted to examine the role of emotional dysregulation in the association between sex and ADHD severity. Results: Females showed a higher frequency of predominantly inattentive presentation; higher rates of mood, anxiety, and eating disorders; and more pronounced emotional dysregulation, affective temperamental traits, personality-related impairment, and biological rhythm disturbances. Observer-rated ADHD severity did not differ by sex, while females reported higher self-rated ADHD severity. Emotional dysregulation was associated with both observer-rated and self-rated ADHD severity, with a stronger association for self-rated symptoms. Mediation analysis showed a significant indirect effect of female sex on self-reported ADHD severity through emotional dysregulation, accounting for 79.4% of the total association. Mixed-effects models further indicated that sex differences in ADHD severity varied according to rating source and persisted, although attenuated, after accounting for emotional dysregulation. Conclusions: Adult females with ADHD showed a different clinical profile, characterized by greater internalizing comorbidity, emotional dysregulation, personality-related impairment, and biological rhythm disturbances. Emotional dysregulation accounted for a substantial part of the higher self-reported ADHD severity observed among females, while rating-source effects suggested that sex differences in adult ADHD may partly depend on how symptom severity is assessed.