Attention deficit disorder with hyperactivity: differential effects of methylphenidate on impulsivity.

The impulsivity component of attention deficit disorder with hyperactivity requires regulation because its effects interfere with children's school performance and persist into adulthood. The present investigation examined the effects of low to intermediate doses of methylphenidate on impulsivity (measured by the Matching Familiar Figures test, a primary index of cognitive tempo) in 14 children with attention deficit disorder with hyperactivity. The mean percentile error score in the highest dose (15 mg) group was significantly lower than those in placebo (P less than .01), 5-mg (P less than .01), and 10-mg (P less than .01) groups. Trend analysis revealed a linear relationship between dose and error score with total errors decreasing as dose increased. Changes in children's error scores were examined using both fixed-dose and milligram per kilogram data-plotting methods. This work demonstrates the need to consider specific task and child characteristics while assessing the child's responsivity to psychostimulants across a range of safe doses and a variety of behavioral domains.