Fluoxetine (Prozac) Dosing Recommendations
For most adults with major depression, start fluoxetine at 20 mg once daily in the morning, which is sufficient to obtain a satisfactory response in most cases. 1
Standard Adult Dosing for Depression
- Initial dose: 20 mg once daily in the morning is the FDA-approved starting dose for major depressive disorder 1
- The dose range is 20-80 mg/day, though 20 mg/day is adequate for most patients 1
- If insufficient clinical improvement occurs after several weeks, consider increasing the dose 1
- Doses above 20 mg/day can be given once daily (morning) or twice daily (morning and noon), with a maximum of 80 mg/day 1
- Full therapeutic effect may be delayed until 4 weeks of treatment or longer 1
Alternative Low-Dose Strategy
For patients with panic disorder or those prone to activation side effects, start at 10 mg/day and increase to 20 mg/day after one week. 1, 2
- Approximately 28% of patients cannot tolerate the full 20 mg dose, with half of these responding well to lower doses 2
- Starting at 5-10 mg and titrating up over one week is particularly useful for patients with concurrent panic disorder, who are more likely to experience intolerable activation 2
Special Population Dosing
Elderly and Dementia Patients
- For elderly patients with dementia and depression, start at 10 mg every other morning, with a maximum of 20 mg every morning 3
- Fluoxetine is activating with a very long half-life and should generally be avoided in older adults due to greater risk of agitation and overstimulation 3
- Lower or less frequent dosing should be used in elderly patients and those with hepatic impairment 1
Pediatric Patients (Children and Adolescents)
- Start with 10 mg/day for one week, then increase to 20 mg/day 1
- For lower weight children, 10 mg/day may be both the starting and target dose 1
- Dose increases to 20 mg/day can be considered after several weeks if insufficient improvement occurs 1
Other Indications
Obsessive-Compulsive Disorder (OCD)
- Adults: Start at 20 mg/day in the morning, with a recommended range of 20-60 mg/day (maximum 80 mg/day) 1
- Adolescents and higher weight children: Start at 10 mg/day, increase to 20 mg/day after 2 weeks, with a range of 20-60 mg/day 1
- Lower weight children: Start at 10 mg/day, with a recommended range of 20-30 mg/day 1
Bulimia Nervosa
- The recommended dose is 60 mg/day administered in the morning, as only this dose was statistically superior to placebo 1
- Titrate up to this target dose over several days for some patients 1
Panic Disorder
- Start at 10 mg/day, then increase to 20 mg/day after one week 1
- The most frequently administered dose in clinical trials was 20 mg/day 1
- Maximum studied dose is 60 mg/day 1
Managing Relapse on Maintenance Therapy
If a patient relapses on fluoxetine 20 mg/day during long-term treatment, increase the dose to 40 mg/day. 4
- In one study, 67% of patients who relapsed on 20 mg/day had full response to 40 mg/day, with an additional 17% showing partial response 4
- Overall, 61% of patients maintained their response on the higher dose during follow-up 4
Important Clinical Considerations
Activation vs. Sedation
- Fluoxetine is generally activating and may cause nervousness, anxiety, agitation, and insomnia, particularly at doses of 60 mg/day and above 5
- Activation symptoms peak early in treatment and decline over time 5
- Some patients experience sedation (somnolence, asthenia), which increases linearly up to 40 mg/day 5
- Discontinuations due to activation or sedation are uncommon 5
Hepatic and Renal Impairment
- Use lower or less frequent dosing in patients with hepatic impairment 1
- Dosage adjustments for renal impairment are not routinely necessary 1
Drug Interactions
- Fluoxetine inhibits CYP2D6 and other cytochrome P450 enzymes, increasing potential for drug interactions, though most are not clinically important 6
- Allow at least 14 days after stopping an MAOI before starting fluoxetine 1
- Allow at least 5 weeks after stopping fluoxetine before starting an MAOI due to its long half-life 1