Implications of early versus late onset of attention-deficit/hyperactivity disorder symptoms

Objective: The current diagnostic criteria for attention-deficit/hyperactivity disorder (ADHD) require that symptoms emerge prior to age 7 in order for a formal diagnosis to be considered. However, this age-of-onset criterion (AOC) has recently been questioned on bath theoretical and empirical grounds. Method: Data from 4 annual waves of interviews with 9- to 16-year-olds from the Great Smoky Mountains Study were analyzed. Results: Confirming previous studies, a majority of youths who had enough symptoms to meet criteria for ADHD were reported to have first exhibited these symptoms prior to age 7. Early onset of ADHD symptoms was associated with worse clinical outcomes in youths with the combined subtype of ADHD but not youths with the inattentive subtype. Conclusions: Findings support the continued inclusion of the AOC for the assessment of the combined but not necessarily the inattentive subtype of ADHD. Too few youths had a late onset of solely hyperactive-impulsive symptoms to evaluate the AOC for that group. However, regardless of the age of onset, youths who had elevated levels of ADHD symptoms were at increased risk for negative outcomes that may necessitate intervention.