Overview: This study investigated the cognitive effects of stimulant medication in children with Attention-Decit / Hyperactivity Disorder (ADHD). Children (11 = 24) were given various medication regimens, and then completed a task measuring impulsivity. The order of treatments was counterbalanced so that each medication regimen appeared equally often in each position (i.e., six children received the placebo rst, six received it second, and so on). The children were on each dose four weeks before testing. Impulsivity is operationalized as the total number of errors (dened as any non-target stimuli to which the child responds) in a task in which children were presented with 540 letters, one at a time every 0.8 seconds with a 0.2 second interval between, and are told to press the left key every time a letter repeated itself. The test differentiates children with and without ADHD, and may be sensitive to medication treatment in children with ADHD. Research question: Is Impulsivity sensitive to different MPH /MPH+supplement treatment in children with ADHD