What is the starting dose of Prozac (fluoxetine)?

Starting Dose of Prozac (Fluoxetine)

The recommended starting dose of Prozac (fluoxetine) for adults with major depressive disorder is 20 mg once daily, administered in the morning. 1

Standard Adult Dosing for Depression

• Start with 20 mg/day in the morning for most adult patients with major depressive disorder 1
• This 20 mg/day dose is sufficient to obtain a satisfactory response in most cases, as demonstrated in controlled trials comparing 20,40, and 60 mg/day doses 1
• The FDA-approved dose range is 20-80 mg/day, with a maximum of 80 mg/day 1
• Dose increases may be considered after several weeks if insufficient clinical improvement is observed 1

Special Population Considerations

Pediatric Patients (Children and Adolescents)

• Start with 10 mg/day for the first week, then increase to 20 mg/day 1
• For lower weight children, the starting and target dose may remain at 10 mg/day due to higher plasma levels 1
• A dose increase to 20 mg/day may be considered after several weeks if response is inadequate 1

Elderly Patients

• Use a lower starting dose than the standard 20 mg/day 2, 1
• For elderly patients with dementia and depression, guidelines recommend starting with 10 mg every other morning, with a maximum of 20 mg every morning 2
• Fluoxetine should generally be avoided in older adults due to greater risk of agitation and overstimulation 2

Patients with Hepatic Impairment

• Use a lower or less frequent dosage in patients with liver disease 1

Important Clinical Considerations

Timing of Full Effect

• The full therapeutic effect may be delayed until 4 weeks of treatment or longer 1
• Patients should be counseled about this delayed onset to maintain adherence 1

Activation Profile

• Fluoxetine tends to be activating and may cause initial anxiety or agitation 2
• Common early adverse events include insomnia, nervousness, nausea, and somnolence, which typically resolve over time 3
• Morning dosing is recommended to minimize sleep disturbance 1

Dosing Flexibility

• Doses above 20 mg/day may be administered once daily (morning) or twice daily (morning and noon) 1
• No dosage adjustments are routinely necessary for renal impairment 1

Common Pitfalls to Avoid

• Do not start with doses higher than 20 mg/day in standard adult patients, as this increases adverse events without improving efficacy 1, 4
• Do not use fluoxetine as first-line in elderly patients due to its activating properties and very long half-life 2
• Do not expect immediate response—counsel patients that 4+ weeks may be needed for full effect 1
• Be cautious with drug interactions as fluoxetine inhibits CYP2D6 and other enzymes 4