Atomoxetine Adult Dosage
For adults with ADHD, start atomoxetine at 40 mg once daily in the morning, then titrate to the target dose of 80 mg daily after a minimum of 3 days, with a maximum dose of 100 mg/day. 1, 2
Initial Dosing Strategy
- Begin with 40 mg orally once daily in the early morning for all adults and patients weighing over 70 kg 1, 2
- After a minimum of 3 days at the initial dose, increase to the target dose of 80 mg daily 1
- The 80 mg dose can be administered either as a single morning dose or divided into two doses (early morning and late afternoon/early evening) 1, 2
Titration Schedule
- Increase the dose every 7-14 days based on clinical response and tolerability, following the sequence: 40 mg → 60 mg → 80 mg daily 1
- The target dose of 1.2 mg/kg/day demonstrates equivalent efficacy to higher doses without additional benefit 1
- Maximum recommended dose is 100 mg/day or 1.4 mg/kg/day, whichever is lower 1, 2, 3
Critical Timing Considerations
Atomoxetine requires 6-12 weeks to achieve full therapeutic effect, unlike stimulants which work within days—this is essential for setting appropriate patient expectations 4
- Maintain patients at the target dose for at least 4-6 weeks before judging efficacy, as premature dose adjustments or discontinuation due to perceived lack of response is a common pitfall 5
- Initial somnolence and gastrointestinal symptoms are particularly common if dosage is increased too rapidly 1
Dosing Flexibility
- Once-daily morning dosing is effective and may improve adherence as an alternative to divided dosing 1, 6
- Both once-daily (80 mg QD) and twice-daily (40 mg BID) strategies are safe, well-tolerated, and efficacious, though nausea frequency is significantly lower with BID dosing (16.4% vs 32.4%, p=0.007) 6
- Prescribers have discretion to base dosing strategies on individual factors, particularly gastrointestinal tolerability 6
Common Pitfall: Underdosing
Real-world data show that an average adult atomoxetine dose of only 60 mg/day is commonly utilized, despite the 80 mg/day target dose recommendation—this suboptimal dosing may be associated with poor patient outcomes 5
- The most common adverse effects include nausea, vomiting, fatigue, decreased appetite, abdominal pain, and somnolence 1, 7
- Slow titration (increasing dose gradually every 1-2 weeks) is generally better tolerated and helps avoid unintentionally exceeding the optimal medication dose 4
Special Populations and Drug Interactions
- SSRIs can elevate serum atomoxetine levels through CYP2D6 inhibition, potentially requiring dose adjustment in patients taking both medications 8, 1
- Approximately 7% of the population are poor CYP2D6 metabolizers with significantly higher plasma levels and longer half-lives, leading to increased adverse effects 1
- Atomoxetine can be administered to patients with end-stage renal disease using the normal dosing regimen, as dose-corrected exposure is similar to healthy subjects 2
Safety Monitoring Requirements
- Monitor closely for suicidal ideation, clinical worsening, and unusual behavioral changes, especially during the first few months of treatment or at dose changes, due to FDA black box warning 8, 1
- Monitor heart rate and blood pressure at baseline and regularly during treatment, as atomoxetine may increase both parameters 1
- Behavioral activation/agitation (including motor or mental restlessness, insomnia, impulsiveness, aggression) can occur early in treatment or with dose increases 4