Fluoxetine Side Effects — What to Expect, When to Worry

Fluoxetine (Prozac) helps a lot of people feel better, but it also comes with side effects. Some are mild and fade in a few weeks. Others need quick medical attention. This page lays out the usual reactions, the rare but serious risks, and easy steps you can try to reduce discomfort.

Common and Less Serious Side Effects

These are the reactions most people notice at the start or after a dose change:

• Gastro upset: nausea, diarrhea, or reduced appetite. Try taking your pill with food if this bothers you.
• Sleep changes: insomnia or feeling sleepy. If you feel wired, take fluoxetine in the morning; if drowsy, talk to your doctor about evening dosing.
• Headache and dizziness: usually temporary. Rest, hydrate, and avoid driving if you feel off-balance.
• Sexual side effects: lower libido, delayed orgasm, or erectile issues. These can be persistent—bring them up with your prescriber.
• Anxiety or jitteriness: sometimes starts when treatment begins. If anxiety gets worse, contact your clinician.

Most of these ease after 2–6 weeks as your body adjusts. Don’t stop the medicine suddenly without advice.

Serious Risks, Interactions, and Practical Tips

Call emergency services or your doctor right away for these signs: severe allergic reaction (rash, swelling, trouble breathing), chest pain, fainting, blackouts, or thoughts of harming yourself. Also watch for unusual bleeding (easy bruising, nosebleeds) because fluoxetine can increase bleeding risk, especially if combined with NSAIDs or blood thinners.

Avoid mixing fluoxetine with MAO inhibitors, certain migraine drugs (triptans), or high doses of tramadol—these can trigger serotonin syndrome, a dangerous condition. Symptoms include high fever, shivering, fast heartbeat, severe agitation, or muscle stiffness. If you suspect serotonin syndrome, get to an ER.

Practical tips to reduce side effects:

• Start low if your doctor recommends it, and increase slowly as tolerated.
• Take it at a consistent time each day to avoid sleep problems.
• Limit alcohol—drinking can make side effects worse and reduce benefit.
• Tell your prescriber about other meds and supplements (like St. John’s wort).

Stopping fluoxetine usually causes fewer withdrawal symptoms than short-acting SSRIs because it stays in your body longer. Still, don’t quit suddenly—work with your provider to taper if needed.

Pregnant or breastfeeding? Discuss risks and benefits with your doctor. Fluoxetine can be used in pregnancy in some cases, but it needs careful planning and monitoring.

If side effects are making life hard, there are options: dose adjustments, switching to a different antidepressant, or adding short-term treatment for specific symptoms. Keep an open line with your prescriber and report any new or worsening problems right away.

Questions to ask your clinician: Is this side effect likely to go away? Should I change my dose or timing? Are there safer alternatives if I want to stop? Clear answers will help you feel safer and more in control while taking fluoxetine.