Maximum Daily Dose of Prozac (Fluoxetine)
The maximum daily dose of fluoxetine (Prozac) is 80 mg per day, which should not be exceeded in any clinical situation. 1
Dosing Guidelines by Indication
Major Depressive Disorder
- Initial dose: 20 mg/day in the morning
- Dose adjustments: May increase after several weeks if insufficient clinical improvement is observed
- Maximum dose: 80 mg/day (can be given once daily or divided into morning and noon doses)
- Pediatric dosing:
- 10-20 mg/day (starting with 10 mg/day in lower weight children)
- After 1 week at 10 mg/day, may increase to 20 mg/day if needed
Obsessive-Compulsive Disorder (OCD)
- Initial dose: 20 mg/day in the morning
- Recommended dose range: 20-60 mg/day
- Maximum dose: 80 mg/day (well tolerated in open studies)
- Pediatric dosing:
- Adolescents/higher weight children: Start with 10 mg/day, increase to 20 mg/day after 2 weeks
- Recommended range: 20-60 mg/day
- Lower weight children: Start with 10 mg/day
- Recommended range: 20-30 mg/day
Bulimia Nervosa
- Recommended dose: 60 mg/day (morning administration)
- Maximum dose: 60 mg/day (doses above this have not been systematically studied)
Panic Disorder
- Dose range: 10-60 mg/day
Special Populations
Hepatic Impairment
- Lower or less frequent dosing should be used
- Dosage adjustments based on clinical response
Elderly Patients
- Lower or less frequent dosing should be considered
- Adjust based on clinical response
Patients with Concurrent Disease/Multiple Medications
- Lower or less frequent dosing should be considered
- Monitor for drug interactions, especially with CYP2D6 inhibitors
Important Considerations
- Therapeutic effect timing: Full therapeutic effect may be delayed until 4-5 weeks of treatment or longer
- Maintenance treatment: Efficacy maintained for up to 38 weeks at 20 mg/day dose
- Weekly dosing option: Available after stabilization on daily dosing
- Drug interactions: Fluoxetine is an inhibitor of CYP2D6 and other CYP enzymes, increasing potential for drug interactions 2
Cautions and Monitoring
- Higher doses (above 20 mg/day) are associated with increased adverse events 2
- Common side effects include gastrointestinal symptoms and nervous system effects
- When switching to or from MAOIs, allow at least 14 days between discontinuing an MAOI and starting fluoxetine, and at least 5 weeks after stopping fluoxetine before starting an MAOI
Clinical Insights
- Some patients who cannot tolerate the standard 20 mg/day dose may benefit from lower doses (5-10 mg/day) 3
- For treatment-resistant depression, doses of 60-80 mg/day have been used effectively with no significant increase in side effects in some studies 4
- The long half-life of fluoxetine and its active metabolite essentially precludes withdrawal phenomena 2
Remember that while the maximum FDA-approved dose is 80 mg/day, the goal should be to use the lowest effective dose that achieves the desired clinical response.