The diagnosis of ADHD will be confirmed by a child and adolescent psychiatrist before participants will be initiated into the study. All patients will be newly diagnosed. Parents were carefully interview and ask to rate the severity of the DSM-IV-TR ADHD symptoms that their children display at home. Children will be excluded if they have a history or current diagnosis of pervasive developmental disorders, schizophrenia or other psychiatric disorders(DSM-IV axis I); any current psychiatric comorbidity that required pharmacotherapy; any evidence of suicide risk and mental retardation (I.Q. <70). In addition, patients will be excluded if they have a clinically significant chronic medical condition, including organic brain disorder, seizures and, current abuse or dependence on drugs within 6 months. Additional exclusion criteria will be hypertension, hypotension. To participate, parents and children have to be willing to comply with all requirements of the study. After a description of the procedures and purpose of the study, written informed consent will be obtained from each patient's parent or guardian. Informed consent will receive before the administration of any study procedure or dispensing of study medication in accordance with the ethical standards of the investigative site's institutional review board and with the Helsinki declaration of 1975, as revised in 2000. The protocol will be approved by the Institutional Review Board (IRB) of Tehran University of Medical Sciences.