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 chil dren (22 nonanxious, 18 anxious) completed a randomized, double-blind, placebo-controlled, crossover trial with three doses (0.3, 0.6, 0.9 m g/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 co morbidly anxious group. By contrast, MPH reduced activity level in bot h groups. The presence of concurrent learning disabilities did not inf luence stimulant response. Conclusions: The presence of comorbid anxie ty in children with ADHD predicts a less robust response to stimulant treatment and suggests that ADHD with anxiety may constitute a distinc t and clinically meaningful subtype of ADHD.