Core symptom of attention deficit disorder with hyperactivity (adhd) is a deficit in inhibition control manifested in learning, information processing and behavioral dysfunction at school and at home. We systematically investigated the effects of methylphenidate (N = 0) and clonidine (N = 7) in a group of 37 children with adhd who showed no evidence of neurological dysfunction at medical evaluation. Medication monitoring was done by means of neuropsychological testing and assessment of behavioral functioning in the home situation, by using the ‘child behavior checklist’, before and eight weeks after medication was started. Methylphenidate and clonidine both showed significant positive effects on sustained attention, information processing, and hyperactive behavior. It was found that only methylphenidate showed significant positive effects on spatial reasoning and aggressive behavior. The difference in effect on aggressive behavior between methylphenidate and clonidine was statistically significant. It is concluded that both types of medication in children with adhd without neurological dysfunction can effectively improve information processing and inhibition control in behavior. We found some different and some similar effects of methylphenidate and clonidine. Neuropsychological testing is not only an important instrument in making a treatment diagnosis of adhd but also in evaluating the effect of medication objectively, for which purpose until now only behavior checklists are used. Especially this should be considered when there is a relative contraindication for prescribing methylphenidate, as in children with neurological dysfunctions, when clonidine can be prescribed.
