Fluoxetine (Prozac): what it treats and how it works

Fluoxetine, often known by the brand name Prozac, is an SSRI antidepressant used for major depression, OCD, bulimia, and panic disorder. It raises serotonin in the brain to improve mood and reduce compulsions and panic. Many people notice some change in 1–2 weeks, but full benefit usually takes 4–6 weeks.

Doses you’ll commonly see

For most adults with depression, doctors start at 20 mg once daily. For OCD or panic disorder, doses often range from 20 to 60 mg. Bulimia is typically treated with 60 mg daily. Some people need higher doses, up to 80 mg, but that decision comes from a prescriber. Older adults usually start lower and move up slowly.

Fluoxetine has a long half-life, which means it stays in the body longer than many other SSRIs. That can make missed doses less risky and withdrawal less abrupt, but you still need a plan if stopping.

Side effects and red flags

Common side effects include nausea, headache, trouble sleeping, tiredness, and changes in sexual function. Many of these get better after a few weeks. Watch for increased anxiety or panic at the start—sometimes the first weeks feel worse before they get better.

Take action right away if you notice severe signs like high fever, stiff muscles, fast heartbeat, fainting, or extreme agitation—these can signal serotonin syndrome and need immediate care. Also report unusual bleeding, severe mood swings, or new suicidal thoughts, especially in people under 25.

Fluoxetine can cause low sodium (rare), trigger manic episodes in people with bipolar disorder, and interact with many drugs. Tell your provider about blood thinners, NSAIDs, other antidepressants, triptans, antipsychotics, and herbal supplements like St. John’s wort.

Fluoxetine is a CYP2D6 inhibitor. That can change how other medications work—examples include some pain meds, certain heart drugs, and tamoxifen. If you’re on complex treatment, ask a pharmacist or clinician for a drug-check.

Pregnancy and breastfeeding decisions depend on risks and benefits. Don’t stop on your own; talk to your clinician about alternatives or monitoring if you’re pregnant or nursing.

Practical tips for starting, stopping, and buying safely

When starting: keep a simple symptom diary for 4–8 weeks so you and your clinician can see progress and side effects. If you miss one dose, take it when you remember the same day; don’t double up.

When stopping: don’t quit suddenly. Even with fluoxetine’s long half-life, a gradual taper over weeks is safer and lowers withdrawal risks like dizziness, vivid dreams, or flu-like symptoms.

Buying online? Use a licensed pharmacy that requires a prescription, shows contact info, and has verifiable reviews. Avoid sites that sell prescription drugs without a prescription or that offer unrealistically low prices. When in doubt, ask your local pharmacist to verify the product and packaging.

If you have questions about dose changes, interactions, or side effects, call your prescriber or a pharmacist. Small, timely steps keep treatment safer and more effective.