Fluoxetine is a generic prescription drug used to treat depression and more. It’s also available as the brand-name drug Prozac. Fluoxetine can cause side effects that range from mild to serious. Examples include sexual problems and abnormal dreams.

Fluoxetine is used in adults to treat the following:

Fluoxetine is also used in some children to treat the following:

  • major depressive disorder (depression)
  • obsessive-compulsive disorder (OCD)
  • depression related to bipolar I disorder in combination with Zyprexa (olanzapine)

Keep reading to learn about the common, mild, and serious side effects that fluoxetine can cause. And for a detailed overview of this drug, check out this in-depth Fluoxetine article.

Fluoxetine has a boxed warning. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Fluoxetine’s side effects explained” section.

Some people may experience mild to serious side effects during their fluoxetine treatment. Examples of the drug’s commonly reported side effects include:

  • sexual problems (see “Fluoxetine’s side effects explained” section)
  • unusual dreams
  • dry mouth
  • diarrhea
  • lack of energy

Mild side effects have been reported with fluoxetine. These include:

  • diarrhea
  • flu-like syndrome
  • difficulty sleeping
  • indigestion
  • sexual problems (see “Fluoxetine’s side effects explained” section)
  • unusual dreams
  • dry mouth
  • lack of appetite which may cause unintentional weight loss
  • lack of energy

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop taking fluoxetine unless your doctor recommends it.

Fluoxetine may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Serious side effects have been reported with fluoxetine. These include:

If you develop serious side effects while taking fluoxetine, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Note: After the FDA approves a drug, it tracks and reviews the side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with fluoxetine, visit MedWatch.

ALLERGIC REACTION

For some people, fluoxetine can cause an allergic reaction.

This side effect occurred in the drug’s studies.

In general, symptoms of an allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking fluoxetine.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to fluoxetine, they may have you switch to a different treatment.

Get answers to some frequently asked questions about fluoxetine’s side effects.

Does increasing your fluoxetine dose raises your risk of developing side effects?

It’s possible. A higher dose of fluoxetine may cause new or worsening side effects. Side effects are most likely to occur during periods when your fluoxetine dosage has just been changed. However, they can occur at any time during treatment too. For example, increasing your fluoxetine dose to 20 milligrams (mg) may cause new or worsening side effects like dry mouth, lack of energy, or indigestion.

Talk with your doctor if you’re experiencing new or worsening side effects after increasing your fluoxetine dose. They may recommend ways to reduce these side effects. They can also reduce your fluoxetine dosage if needed. Your doctor will ultimately want to prescribe the smallest dosage that provides the desired effect.

What side effects should I expect during the first week of fluoxetine treatment?

It depends. Side effects experienced during the first week of fluoxetine treatment can differ from person to person. Common and mild side effects reported with taking fluoxetine include dry mouth, unusual dreams, and diarrhea. These side effects typically become less intense or go away over time.

Serious side effects can also occur, including suicidal thoughts and behaviors. These side effects can develop early on when fluoxetine treatment is started. They’re also more likely to develop during dosage changes. See the “Fluoxetine’s side effects explained” section for more information about suicidal thoughts and behaviors.

Talk with your doctor if you’re experiencing ongoing or bothersome side effects from fluoxetine treatment. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Does fluoxetine cause long-term side effects?

It’s possible. Long-term side effects include those that may start at any time you’re taking a drug, even if you’ve taken it for a long time. It also includes side effects that may not go away, even after you stop taking the drug.

For example, sexual problems were reported to sometimes continue even after stopping fluoxetine treatment. As a result, females and males* may continue to experience low sex drive and other related problems. It’s unknown if or when these symptoms will go away.

Talk with your doctor to learn more about the possible side effects of fluoxetine and how long they may last.

* In this article, we use the terms “male” and “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Learn more about some of the side effects fluoxetine may cause.

Boxed warning: Risk of suicidal thoughts and behaviors

Fluoxetine and other antidepressants have a boxed warning for the risk of suicidal thoughts and behaviors. A boxed warning is the most serious warning from the FDA.

Based on clinical studies, this side effect is more likely to occur in children and young adults ages 24 years old and younger. For this reason, doctors typically will not prescribe this drug for children ages 6 years and younger. This risk is also higher in people taking fluoxetine to treat depression.

Side effects typically develop during the first few months of treatment and during dosage changes. However, they can also happen anytime during your treatment. How long these side effects may last and whether they’ll continue long term is unknown.

Signs of suicidal thoughts and behaviors may include:

  • attempting to harm onself
  • thoughts about harming oneself or dying
  • new or worsening depression, anxiety, or panic attacks
  • feelings of restlessness or irritability
  • difficulty sleeping
  • acting dangerously or aggressively
  • other unusual behavioral or mood changes

What might help

Your doctor will closely monitor you for symptoms of suicidal thoughts and behaviors while you’re taking fluoxetine. They may also recommend you ask your family and close friends to watch for these symptoms. Talk with your doctor right away if your family, friends, or you notice the development of these symptoms. If these symptoms seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Help is out there

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

  • Call or text the 988 Suicide and Crisis Lifeline at 988 or chat at 988lifeline.org. Caring counselors are available to listen and provide free and confidential support 24/7.
  • Text HOME to the Crisis Text Line at 741741 to connect with a volunteer crisis counselor for free and confidential support 24/7.
  • Not in the United States? Find a helpline in your country with Befrienders Worldwide.
  • Call 911 or your local emergency services number if you feel safe to do so.

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you’re not in the same household, stay on the phone with them until help arrives.

Sexual problems

Similar to other selective serotonin reuptake inhibitors, sexual problems were a common side effect reported in fluoxetine’s studies. With this side effect, you may desire sexual activities less and feel that your sexual performance has been affected. This side effect can occur in both males and females.*

Symptoms in males may include:

Symptoms in females may include:

  • low sex drive
  • delayed or inability to have an orgasm

* In this article, we use the terms “male” and “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

What might help

Talk with your doctor if you develop or experience any symptoms of sexual problems. They may recommend ways to reduce these side effects. They can also adjust your fluoxetine dosage or prescribe an alternative medication for your condition.

Keeping track of side effects

During your fluoxetine treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start a new drug or combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Sharing notes with your doctor will help them learn more about how fluoxetine affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before starting treatment with fluoxetine.

Boxed warning: Risk of suicidal thoughts and behaviors

Fluoxetine has a boxed warning. A boxed warning is the most serious warning from the FDA. For details, see the “Side effects explained” section.

Other warnings

Fluoxetine can sometimes cause harmful effects in people with certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether fluoxetine is a good treatment option for you.

Talk with your doctor about your health history before you take fluoxetine. Be sure to tell them if any of the following factors apply to you:

*For additional information about fluoxetine’s drug interactions, see this fluoxetine interactions article.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.