What is the maximum recommended dose of fluoxetine (Prozac) per day?

Maximum Recommended Dose of Fluoxetine

The maximum recommended dose of fluoxetine is 80 mg per day for adults. 1

Dosing Guidelines by Indication

Major Depressive Disorder

• Initial recommended dose is 20 mg/day administered in the morning 1
• Dose increases may be considered after several weeks if insufficient clinical improvement is observed 1
• Doses above 20 mg/day may be administered once daily (morning) or twice daily (morning and noon) 1
• Maximum dose should not exceed 80 mg/day 1
• Systematic evaluation has shown that efficacy in major depression is maintained for up to 38 weeks at 20 mg/day 1

Obsessive-Compulsive Disorder (OCD)

• Initial recommended dose is 20 mg/day administered in the morning 1
• Dose range of 20-60 mg/day is recommended 1
• Doses up to 80 mg/day have been well tolerated in open studies of OCD 1
• Maximum dose should not exceed 80 mg/day 1

Bulimia Nervosa

• Recommended dose is 60 mg/day, administered in the morning 1
• For some patients, titration to target dose over several days may be advisable 1
• Doses above 60 mg/day have not been systematically studied in bulimia 1

Special Populations and Considerations

Hepatic Impairment

• Lower or less frequent dosage should be used in patients with hepatic impairment 1
• This is important as fluoxetine is primarily metabolized by the liver 2

Elderly Patients

• Lower or less frequent dosage should be considered for elderly patients 1
• This reduces the risk of adverse effects while maintaining efficacy 2

Patients with Concurrent Disease or Multiple Medications

• Lower or less frequent dosage should be considered 1
• Fluoxetine is an inhibitor of cytochrome P450 (CYP) 2D6 and other CYP enzymes, which increases potential for drug interactions 2

Common Side Effects and Safety Considerations

• At the standard dose of 20 mg/day, common adverse events affect the gastrointestinal system and nervous system 2
• When higher doses are used (approaching the maximum of 80 mg/day), adverse events become more common 2
• Specific adverse events that occur more frequently with fluoxetine than placebo include insomnia, asthenia, somnolence, decreased libido, and confusion 3
• The long half-life of fluoxetine and its active metabolite (norfluoxetine) essentially precludes a withdrawal phenomenon 2

Clinical Pearls

• Some patients may respond to doses lower than 20 mg/day, particularly those with panic disorder in addition to depression 4
• Starting at lower doses (e.g., 5 mg/day) and gradually increasing may be beneficial for patients who cannot tolerate the standard 20 mg dose 4
• The elimination half-life of fluoxetine is 1-3 days after a single dose, but averages 4 days after long-term administration 5
• Its active metabolite norfluoxetine has an even longer half-life, averaging 7 days after long-term administration 5
• Due to these long half-lives, it takes nearly four weeks to reach steady-state levels in plasma 6

Remember that while the maximum dose is 80 mg/day, the goal should be to use the lowest effective dose that achieves the desired clinical response while minimizing side effects.