Information last reviewed: May 2026 — for educational purposes only.
What Is Fluoxetine (Prozac)?
Fluoxetine, originally marketed as Prozac, is a selective serotonin reuptake inhibitor (SSRI) — the most widely prescribed antidepressant class worldwide. It works by blocking the serotonin transporter (SERT), preventing reuptake of serotonin into the presynaptic neuron and thereby increasing the concentration of serotonin in the synaptic cleft. Fluoxetine has an unusually long half-life (1–4 days for the parent drug; 4–16 days for the active metabolite norfluoxetine), which makes it forgiving of missed doses and gives it a lower risk of discontinuation syndrome compared to shorter-acting SSRIs.
Prescription (Rx) Status
Fluoxetine is prescription-only. Generic fluoxetine is widely available and very inexpensive. It is one of the few antidepressants approved for use in children and adolescents (ages 8+) for major depressive disorder and OCD. Like all antidepressants, it carries an FDA black-box warning for increased suicidal thinking in young patients during early treatment. A weekly fluoxetine capsule formulation (Prozac Weekly, 90 mg) exists for maintenance therapy.
Uses of Fluoxetine
FDA-approved indications: major depressive disorder (MDD), obsessive-compulsive disorder (OCD), bulimia nervosa, panic disorder, and bipolar depression (as Symbyax, combined with olanzapine). Also used off-label for premenstrual dysphoric disorder (PMDD) and generalised anxiety disorder (GAD). The combination of fluoxetine + olanzapine (Symbyax) is specifically approved for treatment-resistant depression.
Capsule Strengths
Fluoxetine oral capsules: 10 mg, 20 mg, and 40 mg. Oral solution: 20 mg/5 mL. Weekly delayed-release capsule: 90 mg. Typical starting dose for depression: 20 mg once daily in the morning. May be titrated to 40–60 mg/day after 4 weeks if needed. Maximum dose: 80 mg/day (OCD).
Price
Generic fluoxetine is among the cheapest antidepressants available. A 30-day supply of 20 mg capsules costs approximately $4–$15 at most pharmacies. Prozac Weekly is more expensive; generic versions are available.
Frequently Asked Questions
Q: How long does fluoxetine take to work?
A: Most patients begin to notice improvement in mood and energy within 2–4 weeks, with full antidepressant effects appearing at 4–6 weeks. Some effects (sleep, appetite, anxiety) may improve earlier.
Q: Does fluoxetine cause sexual dysfunction?
A: Yes — sexual side effects (reduced libido, delayed orgasm, anorgasmia) are common with all SSRIs, including fluoxetine. Discuss with your prescriber if bothersome; dose reduction or switching may help.
Q: Can I stop fluoxetine suddenly?
A: Fluoxetine's long half-life makes discontinuation syndrome less common than with shorter-acting SSRIs, but abrupt stopping is still not recommended. Consult your doctor before stopping.
Disclaimer: This page is for informational purposes only and does not constitute medical advice. Fluoxetine requires a valid prescription. Always consult a qualified healthcare professional. See our full disclaimer.