What is the recommended initial dose of Prozac (fluoxetine) for a patient starting treatment?

Recommended Starting Dose of Prozac (Fluoxetine)

Start with 20 mg once daily in the morning for most adults with depression, as this is the FDA-approved initial dose that provides satisfactory response in the majority of patients. 1

Standard Adult Dosing

• The FDA label specifies 20 mg/day administered in the morning as the recommended initial dose for major depressive disorder in adults. 1
• Clinical trials comparing 20,40, and 60 mg/day to placebo demonstrate that 20 mg/day is sufficient to obtain satisfactory response in most cases. 1
• The full antidepressant effect may be delayed until 4 weeks of treatment or longer, so patience is required before considering dose escalation. 1

Alternative Low-Dose Strategy for Specific Populations

Consider starting at 10 mg daily (or even 5 mg daily) in patients with panic disorder, anxiety disorders, or those who are medication-sensitive. 2, 3

• In one study of 133 depressed outpatients, 28% were unable to tolerate the full 20 mg dose, with half of these patients doing well clinically on lower doses. 3
• Patients with concurrent panic disorder are particularly intolerant of the standard 20 mg dose and benefit from gradual titration starting at 5 mg daily. 3
• The American Academy of Child and Adolescent Psychiatry recommends a "test dose" strategy when anxiety is a concern, starting lower and increasing gradually. 2

Special Population Considerations

Reduce the starting dose to 10 mg daily (or use less frequent dosing) in elderly patients, those with hepatic impairment, or patients on multiple medications. 1

• The FDA label explicitly states that lower or less frequent dosing should be used in patients with hepatic impairment and the elderly. 1
• The American Academy of Family Physicians recommends approximately 50% of the standard adult starting dose in elderly patients due to significantly greater risk of adverse drug reactions. 2
• CYP2D6 poor metabolizers require cautious dosing starting at 10 mg daily due to 3.9 to 11.5-fold higher fluoxetine levels and significantly increased toxicity risk. 2

Pediatric Dosing (Children and Adolescents)

Start with 10 mg daily in pediatric patients, increasing to 20 mg after one week. 1

• Lower weight children may remain at the 10 mg daily target dose due to higher plasma levels. 1
• After one week at 10 mg/day, increase to 20 mg/day in most pediatric patients. 1

Critical Titration Principles

• If dose escalation is needed, wait at least 3-4 weeks between increases (not 1-2 weeks) due to fluoxetine's exceptionally long half-life. 2
• Fluoxetine has a half-life of 1-3 days for the parent compound and 4-16 days for its active metabolite norfluoxetine, meaning steady-state is not reached until approximately 5-7 weeks after a dose change. 2, 4
• Use the smallest available increments (5-10 mg increases) when titrating upward. 2
• The maximum FDA-approved dose is 80 mg/day, though doses above 20 mg are associated with more adverse effects. 1, 5

Common Pitfalls to Avoid

• Do not increase the dose too quickly. The long half-life means side effects may not manifest for several weeks, and premature dose escalation can lead to cumulative toxicity. 2
• Morning dosing is preferred because fluoxetine is activating and may cause insomnia if taken later in the day. 2, 1
• The most common initial adverse effects are gastrointestinal (nausea, diarrhea) and nervous system effects (anxiety, insomnia, nervousness, headache), which are dose-related. 5, 4
• Consider CYP2D6 genetic testing if unexpected adverse effects occur at standard doses, as poor metabolizers have dramatically elevated drug levels even at 20 mg daily. 2