Comorbidity in ADHD: Implications for research, practice, and DSM-V

Objective: Since the introduction of DSM-III/III-R, clinicians and investigators have shown increasing interest in the study of conditions comorbid with attention-deficit hyperactivity disorder (ADHD). Better understanding ADHD comorbidity patterns is needed to guide treatment, research, and future classification approaches. Method: The ADHD literature from the past 15 years was reviewed to (1) explore the most prevalent patterns of ADHD comorbidity; (2) examine the correlates and longitudinal predictors of comorbidity; and (3) determine the extent to which comorbid patterns convey unique information concerning ADHD etiology, treatment, and outcomes. To identify potential new syndromes, the authors examined comorbid patterns based on eight validational criteria. Results: The largest available body of literature concerned the comorbidity with ADHD and conduct disorder/aggression, with a substantially smaller amount of data concerning other comorbid conditions. In many areas the literature was sparse, and pertinent questions concerning comorbidity patterns remain unexplored. Nonetheless, available data warrant the delineation of two new subclassifications of ADHD: (1) ADHD, aggressive subtype, and (2) ADHD, anxious subtype. Conclusions: Additional studies of the frequency of comorbidity and associated factors are greatly needed, to include studies of differential effects of treatment of children with various comorbid ADHD disorders, as well as of ADHD children who differ on etiological factors.