Axis I and II Comorbidity in Adults With ADHD

Ongoing debate over the validity of the attention-deficit/hyperactivity disorder (ADHD) construct in adulthood is fueled in part by uncertainty regarding implications of potentially extensive yet incompletely described comorbid Axis I and II psychopathology. Three hundred sixty-three adults ages 18 to 37 completed semistructured clinical interviews; informants were also interviewed, and best estimate diagnoses were obtained. Results were as follows: First, ADHD combined type (ADHD-C) had an excess of externalizing and internalizing Axis I disorders, suggesting a gradient-of-severity relationship between it and ADHD inattentive type (ADHD-I). Second, ADHD-C and ADHD-I did not differ in frequency of Axis II disorders. Third, however, ADHD overall was associated with increased rates of Axis II disorders, compared with rates in non-ADHD control participants, including both Cluster B (primarily borderline personality disorder) and Cluster C disorders. Fourth, ADHD incrementally accounted for clinician-rated global assessment of functioning scores above and beyond comorbid conditions or symptoms on either Axis I or Axis II. Results further inform nosology of ADHD in adults.