OBJECTIVES: Atomoxetine seems to be as effective for treating attention-deficit/hyperactivity disorder (ADHD) when the daily dose is administered once in the morning as when the dose is divided and administered in the morning and evening. In the present study, the efficacy of atomoxetine administered once daily among children with ADHD was assessed throughout the day, including the evening and early morning. Another goal was to determine how early in treatment it was possible to discern a specific effect of the drug on ADHD symptoms.METHODS: This study was a randomized, multicenter, double-blind, placebo-controlled trial conducted at 12 outpatient sites in the United States. A total of 197 children, 6 to 12 years of age, who had been diagnosed as having ADHD, on the basis of the Diagnostic and Statistical Manual of Mental Disorders (4th ed.) criteria, were randomized to receive 8 weeks of treatment with atomoxetine or placebo, dosed once daily in the mornings. ADHD symptoms were assessed with parent and investigator rating scales. The primary outcome measure was the Attention-Deficit/Hyperactivity Disorder Rating Scale-IV-Parent Version: Air Max Thea Investigator-Administered and Scored total score. Daily parent assessments of children\'s home behaviors in the evening and early morning were recorded with an electronic data entry system. This instrument measures 11 specific morning or evening activities, air Max Nz including getting up and out of bed, doing or completing homework, and sitting through dinner.RESULTS: Seventy-one percent of the children enrolled were male, 69% met criteria for the combined subtype (both inattentive and hyperactive/impulsive symptoms), and the most common psychiatric comorbidity was oppositional defiant disorder (35%). Once-daily atomoxetine (final mean daily dose of air Max Thea Nz 1.3 mg/kg) was significantly air Max more effective than placebo in treating core symptoms of ADHD. Mean reductions in the Attention-Deficit/Hyperactivity Disorder Rating Scale-IV-Parent Version: Investigator-Administered and Scored total score were significantly greater for patients randomized to atomoxetine, beginning at the first visit after the initiation of treatment and continuing at all subsequent visits. Both inattentive and hyperactive/impulsive symptom clusters were significantly reduced with atomoxetine, compared with placebo. With continued treatment and dose titrations, core symptoms of ADHD continued to decrease throughout the 8-week study. Mean reductions in the daily parent assessment total scores for patients randomized to atomoxetine were superior during the first week, beginning with the first day of dosing, and were also superior at endpoint. Efficacy outcomes for the evening hours for atomoxetine-treated patients were superior to those for placebo-treated patients, as assessed with 2 different assessment scales. Decreases in the daily parent assessment morning subscores at endpoint showed a significant reduction in symptoms that lasted into the mornings. Rates of discontinuations attributable to adverse events were <5% for both groups. Adverse events reported significantly more frequently with atomoxetine were decreased appetite, somnolence, and fatigue.CONCLUSIONS: Among children 6 to 12 of age who had been diagnosed as having ADHD, once-daily administration of atomoxetine in the morning provided safe, rapid, continuous, symptom relief that lasted not only into the evening hours but also into the morning hours. Atomoxetine treatment was safe and well tolerated.