A Study in Attention Deficit Hyperactivity Disorder in Children and Adolescents

The main purpose of the study is to help to understand the effect on children and adolescents who are stable on treatment with atomoxetine or osmotic-release oral system (OROS) methylphenidate for attention-deficit/hyperactivity disorder (ADHD) of not taking the medication for a maximum of 6 days over a 28-day study treatment period.

The present study is designed to assess the effect of missed doses of daily medication (off-days). On the off-days the patient will take a placebo (sugar pill). Over the 4 weeks of the actual study there will be 6 random off-days of study medicine and neither the caregiver, patient nor study doctor will know which days are the missing days.

To cover all aspects of the patients' lives and notably their school time, aside from investigator's assessments, evaluations will also be performed on a daily basis by those involved in their day-to-day life: parents, teachers (on school days) and the patients themselves, using an electronic diary.

Eligibility Criteria:
Inclusion Criteria:

* Patients must meet the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition Text Revision (DSM-IV-TR) diagnostic criteria for attention-deficit/hyperactivity disorder (ADHD), confirmed at screening by administering the Kiddie Schedule for Affective Disorders and Schizophrenia for School Aged Children-Present and Lifetime Version.
* Patients must have an Attention-Deficit/Hyperactivity Disorder Rating Scale - IV - Parent Version: Investigator Administered and Scored, total score of less than or equal to 20 at screening and baseline.
* Patients must have a Clinical Global Impression-Attention-Deficit/Hyperactivity Disorder-Improvement score of 1 ("very much better") or 2 ("much better") at screening and baseline.
* Patients must have been taking either atomoxetine or osmotic-release oral system methylphenidate for the treatment of ADHD between 3 and a maximum of 15 months prior to screening.
* Patients must have been receiving the same dose of atomoxetine or osmotic-release oral system methylphenidate as monotherapy in a single daily dose during the 4 weeks prior to screening.
* For females of child-bearing potential only: Test negative for pregnancy at the time of entry based on a urine pregnancy test
* Signed informed consent document (ICD)

Exclusion Criteria:

* Patients who weigh less than 20 kilograms (kg) or more than 70 kg at study entry
* Documented history of bipolar disorder, any history of psychosis or pervasive development disorder.
* Patients with a history of any seizure disorder or patients who have taken anticonvulsant treatment for seizure control.
* Patients at serious suicidal risk.
* History of severe allergies to more than one class of medications or have had multiple adverse drug reactions.
* Patients with acute or unstable medical conditions including cardiovascular disease and hypertension.
* Patients taking excluded concomitant medications or likely to begin structured psychotherapy for ADHD.
* Patients who are currently enrolled in, or discontinued within the last 30 days from a clinical trial.
* Sexually active females who do not use a medically acceptable method of contraception.