Maximum Dose of Prozac (Fluoxetine)

The maximum recommended dose of Prozac (fluoxetine) is 80 mg/day for adults, as specified by the FDA-approved labeling. 1

Standard Dosing Framework

For major depressive disorder, the FDA recommends starting at 20 mg/day in the morning, which is sufficient for most patients to achieve satisfactory response. 1
Doses above 20 mg/day may be administered once daily (morning) or twice daily (morning and noon), but should not exceed 80 mg/day maximum. 1
The American Psychiatric Association confirms that doses of 20-60 mg have been used in clinical trials for major depression, with 20 mg/day being sufficient for most patients. 2

If increasing the dose, wait several weeks at each dose level before escalating further, as the full antidepressant effect may be delayed until 4 weeks of treatment or longer. 1
For fluoxetine specifically, dose increases should occur at 3-4 week intervals, not 1-2 weeks, due to its exceptionally long half-life (1-3 days for fluoxetine, 4-16 days for norfluoxetine), meaning steady-state is not reached until approximately 5-7 weeks after a dose change. 2
Use the smallest available increments (5-10 mg increases) when titrating upward. 2

For obsessive-compulsive disorder (OCD), higher doses of 40-60 mg daily are typically necessary and more effective than lower doses, as OCD generally requires higher SSRI doses compared to depression. 2, 3
Meta-analyses confirm greater efficacy at higher doses for OCD, with expert guidelines recommending an optimal fluoxetine dose of 40-60 mg daily for this indication. 3

Higher doses above 20 mg/day are associated with more frequent adverse events. 1, 4
Common adverse effects at standard 20 mg dosing include insomnia, asthenia, somnolence, gastroenteritis, decreased libido, chills, and confusion, which occur more frequently than placebo. 5
Higher SSRI dosing is associated with increased dropout rates due to adverse effects, particularly during the first few weeks when plasma levels are still rising. 2

For elderly patients, use lower or less frequent dosing—approximately 50% of the standard adult starting dose—due to significantly greater risk of adverse drug reactions. 2, 1
For patients with hepatic impairment, a lower or less frequent dosage should be used. 1
Dosage adjustments for renal impairment are not routinely necessary. 1

CYP2D6 poor metabolizers have 3.9 to 11.5-fold higher fluoxetine levels and are at significantly higher risk of toxicity even at standard doses, with the FDA issuing safety warnings about QT prolongation risk in this population. 2
If a patient develops unexpected adverse effects or seems unusually sensitive to dose increases, consider CYP2D6 testing before escalating to higher doses. 2
For known CYP2D6 poor metabolizers, start at 10 mg daily with cautious titration and avoid pushing toward the 80 mg maximum. 2

For children and adolescents with major depressive disorder, start with 10 or 20 mg/day, increasing to 20 mg/day after 1 week if starting at 10 mg. 1
In lower weight children, the starting and target dose may be 10 mg/day due to higher plasma levels in this population. 1