Available Strengths of Prozac (Fluoxetine)
Prozac (fluoxetine) is available in 10 mg, 20 mg, 40 mg, and 90 mg formulations, with 20 mg being the standard starting dose for most adults with depression.
Available Formulations
- Capsules: 10 mg, 20 mg, 40 mg
- Delayed-release capsules (Prozac Weekly): 90 mg
- Oral solution: 20 mg/5 mL (liquid formulation)
- Tablets: 10 mg, 20 mg (in some markets)
Dosing Information by Indication
Major Depressive Disorder
- Initial dose: 20 mg once daily in the morning
- Dose range: 20-80 mg daily
- Lower starting doses (5-10 mg) may be beneficial for patients with panic disorder or those sensitive to medication side effects 1
Obsessive-Compulsive Disorder
- Initial dose: 20 mg daily
- Effective dose range: 20-60 mg daily
- Higher dosing (60-80 mg) may provide superior efficacy for OCD 2
Other FDA-Approved Indications
- Bulimia nervosa: 60 mg daily
- Panic disorder: 10-20 mg daily initially, may increase to 60 mg
- Premenstrual dysphoric disorder: 20 mg daily
Pharmacokinetic Considerations
- Half-life: 1-3 days after single dose; averages 4 days after long-term administration 3
- Active metabolite (norfluoxetine): Has a half-life of approximately 7 days 3
- Steady-state plasma concentrations: Fluoxetine plus norfluoxetine therapeutic range is 120-300 ng/mL 2
- Protein binding: Approximately 94% 3
Special Populations
Elderly Patients
- Consider starting at lower doses (10 mg daily)
- Fluoxetine has shown similar efficacy to doxepin in geriatric patients 4
Children and Adolescents
- Only antidepressant FDA-approved for depression in children aged 8 years or older 2
- Typical starting dose is lower than adult dose
Important Clinical Considerations
- Dose titration: When increasing dose, allow at least several weeks between dose increases due to the long half-life of fluoxetine and its active metabolite
- Low-dose options: Starting with 5 mg daily and gradually increasing may improve tolerability, particularly in patients with comorbid panic disorder 1
- Drug interactions: Fluoxetine is an inhibitor of CYP2D6 and other CYP enzymes, which increases potential for drug interactions 5
Common Side Effects
Most common side effects at the standard 20 mg dose include:
- Nausea
- Anxiety
- Insomnia
- Anorexia
- Diarrhea
- Nervousness
- Headache 3
Side effects are generally dose-related, with higher incidence at doses above 20 mg daily 5.