Starting Dose for Atomoxetine
For children and adolescents weighing up to 70 kg, start atomoxetine at approximately 0.5 mg/kg/day, and for those over 70 kg and adults, start at 40 mg once daily. 1, 2
Weight-Based Dosing for Pediatric Patients (≤70 kg)
- Initial dose: 0.5 mg/kg/day administered either as a single morning dose or divided into two doses (morning and late afternoon/early evening) 1, 2, 3
- Maintain this starting dose for at least 1-2 weeks to assess tolerability before any dose increase 1
- After the initial period, titrate to a target dose of 1.2 mg/kg/day based on clinical response 1, 2, 4
- Maximum dose: 1.4 mg/kg/day or 100 mg/day, whichever is lower 1, 2
The FDA label confirms that doses of 0.5 mg/kg/day showed intermediate efficacy in clinical trials, while 1.2 mg/kg/day and 1.8 mg/kg/day demonstrated superior efficacy, with no additional benefit at the higher dose 3, 4. This supports starting conservatively and titrating to 1.2 mg/kg/day as the optimal target.
Fixed Dosing for Patients >70 kg and Adults
- Initial dose: 40 mg once daily 1, 2
- Maintain for at least 1-2 weeks before increasing 1
- Titrate in increments of 10-25 mg every 1-2 weeks based on response and tolerability 1
- Maximum dose: 100 mg/day 1, 2
Critical Titration Principles
Slow, gradual dose escalation is essential to minimize adverse effects, particularly behavioral activation (agitation, restlessness, impulsiveness, aggression) which can occur early in treatment or with rapid dose increases 1. Younger patients are especially susceptible to these effects with aggressive titration 1.
- Increase doses by the smallest available increments at approximately 1-2 week intervals 1
- If side effects emerge, consider returning to the previous well-tolerated dose 1
- Dose adjustments should typically occur every 7-14 days following a sequential, weight-based approach 2
Dosing Schedule Options
Atomoxetine can be administered flexibly based on tolerability:
- Once-daily dosing (morning or evening) is effective and convenient 2, 5
- Split dosing (morning and late afternoon/evening) may reduce side effects initially, with option to consolidate to once-daily later 1, 2
Clinical trials demonstrate that once-daily morning dosing provides continuous symptom relief lasting through evening and into the next morning 5.
Important Clinical Considerations
Delayed onset of action: Unlike stimulants that work within hours, atomoxetine requires 6-12 weeks to achieve full therapeutic effect 1, 2. Setting appropriate patient expectations about this timeline is critical to prevent premature discontinuation.
Common adverse effects during initial titration include nausea, vomiting, fatigue, decreased appetite, abdominal pain, and somnolence 1, 2. These are generally dose-related and can be minimized with slow titration.
CYP2D6 poor metabolizers (approximately 7% of Caucasians, 2% of African Americans) experience 10-fold higher drug exposure and may require dose adjustments 2, 3.
Safety Monitoring
- Black Box Warning: Monitor closely for suicidal ideation, especially during the first few months of treatment or with dose changes 1, 2
- Obtain baseline and monitor blood pressure, heart rate, height, and weight at follow-up visits 6, 2
- Assess response after 6-12 weeks, as full therapeutic effects take time to develop 2
Special Populations
For patients with end-stage renal disease, no dose adjustment is necessary—use the normal dosing regimen 3.
In patients with comorbid tic disorders, anxiety disorders, or autism spectrum disorder, atomoxetine may be considered first-line and should follow the same starting dose guidelines 2, 7.