Clonidine in Attention Deficit Hyperactivity Disorder (ADHD) in Children

This trial will compare the benefits and side effects of two medications-clonidine and methylphenidate (MPH)-used alone or in combination to treat ADHD in children. MPH is FDA-approved for the treatment of ADHD symptoms in children, and clonidine is FDA-approved for the treatment of hypertension in adults. Stimulant medications such as MPH are known to be safe and effective for the treatment of many ADHD symptoms. Such medicines, however, do not cure the condition or improve all of the symptoms of ADHD, and the long-term effectiveness of these medications is not well-known. In this study the participants will be randomly selected to receive one of four treatments: 1.) clonidine; 2.) MPH; 3.) clonidine and MPH; or 4.) a placebo (which is not an active medication, but a substance that is thought to have no biological effect). The time participation in the study is 16 weeks.