DIFFERENTIAL-EFFECTS OF METHYLPHENIDATE ON WORKING-MEMORY IN ADHD CHILDREN WITH AND WITHOUT COMORBID ANXIETY

Objective: To examine the effects of methylphenidate (MPH) on working memory and behavior in anxious and nonanxious children with attention-deficit hyperactivity disorder (ADHD). Method: A total of 40 ADHD children (22 nonanxious, 18 anxious) completed a randomized, double-blind, placebo-controlled, crossover trial with three doses (0.3, 0.6, 0.9 mg/kg) of MPH. A serial addition task was used to assess working memory; direct observation of motor activity indexed behavior. Results: MPH improved working memory in the nonanxious ADHD group but not in the comorbidly anxious group. By contrast, MPH reduced activity level in both groups. The presence of concurrent learning disabilities did not influence stimulant response. Conclusions: The presence of comorbid anxiety in children with ADHD predicts a less robust response to stimulant treatment and suggests that ADHD with anxiety may constitute a distinct and clinically meaningful subtype of ADHD.