Fluoxetine (Prozac)

Sean Jackson
Author: Sean Jackson Medical Reviewer: Dr. Brittany Ferri, PhD Last updated:

Fluoxetine is an antidepressant medication commonly sold under the brand name Prozac that’s useful in treating mood disorders, bulimia nervosa, and obsessive-compulsive disorder, among others. As with any drug, there are risks associated with taking fluoxetine, including headaches, dry mouth, irregular heartbeat, and seizures.[1]

Fluoxetine brand names

Fluoxetine is more commonly known by its brand name, Prozac. Other names include Prozac Weekly, Sarafem, Rapiflux, and Selfemra. The primary difference between these versions of fluoxetine is their dosage level.

For example, Prozac comes in 10mg, 20mg, and 40mg capsules. Prozac Weekly comes in 90mg delayed-release capsules. Sarafem is available in 10mg and 20mg tablets. Fluoxetine is available in generic form, too. Capsules (10mg, 20mg, or 40mg), delayed-release capsules (90mg), tablets (10mg, 20mg, or 60mg), and liquid (20mg) are available.[1]

What is fluoxetine prescribed for?

Though fluoxetine is traditionally associated with treating depression, its uses go far beyond that. Below is a short list of the primary conditions for which it’s prescribed and a few less-common uses.

Depressive disorders – Fluoxetine is commonly prescribed for treating depressive disorders, including major depression. It increases serotonin levels in the brain, which helps improve mood.[2]

Obsessive-compulsive disorder – Fluoxetine is effective in reducing obsessions (intrusive thoughts) and compulsions (the need to perform specific behaviors) in OCD. Fluoxetine can reduce these symptoms by 40-60 percent.[3]

Panic attacks – Panic attacks are a hallmark symptom of panic disorder. Studies show that 20mg of fluoxetine reduces the frequency of attacks while also elevating mood.[4]

Bulimia nervosa – Fluoxetine (60mg) reduces two common symptoms – binge eating and vomiting – in the first few weeks of treating bulimia. Long-term usage of Prozac results in a 50 percent reduction in binge eating and vomiting.[5]

Premenstrual dysphoric disorder (PMDD)Premenstrual dysphoric disoder is characterized by tension, irritability, and depression in the days before menstruation. These symptoms typically end at the onset of menstruation. Fluoxetine helps manage these symptoms.[1]

Less commonly, Prozac is a treatment for the following:

It should be noted that Prozac is not approved by the Federal Drug Administration (FDA) to treat the mental health conditions listed above.[1] Therefore, it’s considered an off-label treatment, although this doesn’t necessarily mean it’s unsafe. You and your doctor should thoroughly discuss the decision to prescribe Prozac for these conditions.

How does Prozac work?

Prozac works by inhibiting serotonin reuptake in the brain (thus, it’s a selective serotonin-reuptake inhibitor, or SSRI). Prozac and other SSRIs help elevate mood, improve sleep, and regulate emotions by preventing serotonin reuptake.[6]

Prozac’s effect is not immediate, though. Typically it takes one to two weeks before you begin to feel the physical effects of the drug (e.g., improved sleep, better energy). You might feel worse in the initial weeks of taking this medication. Usually, it takes about six weeks for Prozac to take full effect and improve mood.

Not everyone responds well to Prozac. If your symptoms haven’t improved after about six weeks, talk with your mental health provider to determine if a change in course is needed. If your doctor determines that you should no longer be on Prozac, they will order a gradual reduction in dosage to minimize the risk of withdrawal symptoms.[2]

How is fluoxetine usually taken?

Prozac is taken orally, with or without food. As noted earlier, Prozac is available in capsules, delayed-release capsules, tablets, and liquid forms. The typical dosage for adults is 20mg (10mg for children), though the dosage varies from one person to the next. Likewise, the dosage starts small and builds up over time.

Prozac is a once-daily drug in most situations. It’s best to take Prozac at the same time each day. If you have difficulty sleeping, taking this drug in the morning is advisable.[7]

Once you begin treatment with fluoxetine, you’ll likely continue taking it for several months. Mental health providers typically prefer patients to continue taking the drug for six to twelve months after depressive symptoms have stopped.

How long does fluoxetine stay in your system?

The half-life of Prozac is initially about one to three days, though with continued use, that extends to four to six days. The drug is 99 percent out of your body after about 25 days.[8] This is an exceptionally long time. For comparison, many SSRIs (e.g., Paxil, Zoloft, Lexapro) have a half-life of around one day and are 99 percent out of the body in four to six days.[9]

The long half-life of Prozac means you can miss a dose and likely avoid any negative effects. However, its long half-life also means that it stays in your system longer. For example, Prozac can show up in urine and blood analyses for up to three months after you stop using the drug.[9]

Prozac side effects

Many people can safely take fluoxetine for a long time with no side effects or very mild side effects.[6] However, it’s important to understand what side effects are possible with long-term use – this helps you monitor physical and psychological changes to discuss with your doctor.

It’s helpful to categorize the fluoxetine adverse effects as mild and severe. In both cases, psychological and physiological side effects might occur.

Mild side effects include, but are not limited to:[10]

  • Nervousness and anxiety
  • Anxiety
  • Loss of appetite
  • Weight loss
  • Diarrhea
  • Nausea
  • Difficulty sleeping (particularly falling asleep or staying asleep)
  • Dry mouth
  • Uncontrollable shaking

Additionally, both males and females might experience sexual problems (e.g., decreased sex drive, delayed orgasm). Excessive sweating, headache, and confusion are further side effects of which to be aware.

Severe fluoxetine side effects include, but are not limited to:[10]

  • Rash, blisters, hives, or itching
  • Difficulty breathing or swallowing
  • Joint pain
  • Irregular heartbeat
  • Seizures
  • Abnormal bruising or bleeding
  • Shortness of breath
  • Dizziness
  • Fainting
  • Swelling of the hands, feet, lower legs, or ankles
  • Swelling of the face, eyes, lips, tongue, or throat

Furthermore, some patients experience fever, agitation, and severe muscle stiffness. Hallucinations, confusion, and shivering are additional severe side effects. The development of angle-closure glaucoma (a condition in which severe eye pressure develops and can lead to vision loss) might also occur.

More seriously, the Federal Drug Administration (FDA) also warns that taking fluoxetine might result in increased suicidal ideation and behaviors.

If you or someone you know is taking Prozac and experiencing any of the severe conditions listed above, consult a medical professional immediately. Mild side effects often improve over time (though sexual side effects often persist). However, if mild side effects concern you, get in touch with your doctor.

Fluoxetine precautions

Before taking Prozac, it’s important to discuss with your doctor any other medications you’re taking, as interactions between Prozac and other types of drugs might pose a risk of increased side effects. Also, discuss herbal and nutritional supplements you’re taking or have taken recently.

Review any physiological concerns with your physician as well. This includes allergies to any medications, if you’re pregnant, or if you have a family history of heart problems. Likewise, tell your doctor if any of the following apply to you:

  • Low levels of sodium, potassium, or magnesium
  • Recent heart attack or stroke
  • High blood pressure or bleeding problems
  • Diabetes
  • Seizures
  • Kidney disease

If you and your doctor decide to start fluoxetine as a treatment for your depression, be aware that it can make you drowsy. You might need to refrain from driving until you understand how the drug affects your judgment, cognition, and reaction time.

Fluoxetine interactions

A primary concern with Prozac is its interaction with monoamine oxidase inhibitors, or MAOIs (e.g., Nardil, Emsam, Parnate).[1] In rare cases, the combination of Prozac and other medications that increase serotonin can lead to serotonin syndrome. The symptoms of serotonin syndrome include:

  • Severe muscle tightness
  • Fever
  • Diarrhea
  • Shivering
  • Confusion
  • Seizures

In some instances, serotonin syndrome might also result in death.

To avoid this interaction, you should not take fluoxetine with MAOIs or within six weeks of taking an MAOI. Other antidepressant drugs, amphetamines, triptans (which are used to treat migraines), and pain medications (like tramadol) should also be avoided.[1]

Prozac storage

Proper storage of Prozac includes keeping it in its original prescription bottle with the lid closed tightly. Store it at room temperature and away from excess heat, moisture, or light. Therefore, the bathroom is not a good location to keep Prozac. Also keep the medication out of the reach of children.

If Prozac isn’t stored properly, poisoning or overdose might occur (e.g., if a child finds an opened prescription bottle). If you’re concerned that your prescription is damaged or outdated, contact your doctor or pharmacist.

What to do if you overdose on fluoxetine

A fluoxetine overdose presents a significant health risk and should be treated as an emergency, particularly if any of the following symptoms have occurred:[10]

  • Dizziness, fainting, or seizures
  • Hallucinations
  • Nervousness
  • Confusion
  • Unsteadiness or uncontrollable shaking

Furthermore, an overdose of Prozac might cause an irregular heartbeat, difficulty breathing, unresponsiveness, or coma. If any of these symptoms occur, contact emergency services immediately.

Frequently asked questions about Prozac

Does fluoxetine cause weight gain?

Fluoxetine does not contribute to weight gain. Instead, some patients experience a reduced appetite that leads to weight loss.[6]

Can you take fluoxetine when pregnant?

You can take fluoxetine when pregnant. It’s also safe to take fluoxetine while breastfeeding. There is no known evidence that fluoxetine reduces fertility, either.[11]

Fluoxetine vs Citalopram: What’s the difference?

Both fluoxetine and citalopram are SSRIs, but only fluoxetine is approved for use in some children. Likewise, fluoxetine can treat more conditions than citalopram. Where citalopram can treat major depressive disorder, fluoxetine can treat OCD, panic disorder, bulimia nervosa, and premenstrual dysphoric disorder.[1]

  1. National Alliance on Mental Illness. (2020, December). Fluoxetine: Prozac. Retrieved October 17, 2022, from https://www.nami.org/About-Mental-Illness/Treatments/Mental-Health-Medications/Types-of-Medication/Fluoxetine-(Prozac)
  2. National Health Service. (2022, February 10). About fluoxetine. Retrieved October 17, 2022, from https://www.nhs.uk/medicines/fluoxetine-prozac/about-fluoxetine/
  3. International OCD Foundation. (n.d.). Medications for OCD. Retrieved October 17, 2022, from https://iocdf.org/about-ocd/ocd-treatment/meds/
  4. Apgar, B. (1999). Fluoxetine for treatment of panic disorder. American Family Physician, 59(7), 1924-1926. https://www.aafp.org/pubs/afp/issues/1999/0401/p1924.html
  5. Bello, N. T., & Yeomans, B. L. (2018). Safety of pharmacotherapy options for bulimia nervosa and binge eating disorder. Expert opinion on drug safety, 17(1), 17–23. https://doi.org/10.1080/14740338.2018.1395854
  6. National Health Service. (2022, February 10). Common questions about fluoxetine. Retrieved October 17, 2022, from https://www.nhs.uk/medicines/fluoxetine-prozac/common-questions-about-fluoxetine/
  7. National Health Service. (2022, February 10). How and when to take fluoxetine. Retrieved October 18, 2022, from https://www.nhs.uk/medicines/fluoxetine-prozac/how-and-when-to-take-fluoxetine/
  8. Harvard Health Publishing. (2022, May 15). Going off antidepressants. Retrieved October 18, 2022, from https://www.health.harvard.edu/diseases-and-conditions/going-off-antidepressants
  9. Family Recovery Specialists. (n.d.) How long does Prozac stay in your system (urine and more). Retrieved October 18, 2022, from https://familyrecoveryspecialists.com/prozac/stay-in-system/
  10. Medline Plus. (2022, January 15). Fluoxetine. Retrieved October 19, 2022, from https://medlineplus.gov/druginfo/meds/a689006.html#side-effects
  11. National Health Service. (2022, February 10). Pregnancy, breastfeeding and fertility while taking fluoxetine. Retrieved October 19, 2022, from https://www.nhs.uk/medicines/fluoxetine-prozac/pregnancy-breastfeeding-and-fertility-while-taking-fluoxetine/
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Sean Jackson
Author Sean Jackson Writer

Sean Jackson is a medical writer with 25+ years of experience, holding a B.A. degree from the University of Nottingham.

Published: Nov 22nd 2022, Last edited: Nov 10th 2023

Brittany Ferri
Medical Reviewer Dr. Brittany Ferri, PhD OTR/L

Dr. Brittany Ferri, PhD, is a medical reviewer and subject matter expert in behavioral health, pediatrics, and telehealth.

Content reviewed by a medical professional. Last reviewed: Nov 23rd 2022