The Side Effects of Fluoxetine

Awareness of side effects helps individuals make informed decisions about their treatment. Moreover, identifying side effects promptly and communicating them to doctors, pharmacists, and health authorities can empower people to improve their care.

This article contains awareness about the side effects of a drug commonly used for treating several mental health disorders, including bipolar disorder, depressive disorder, and manic disorder. This drug is called Fluoxetine and is available in the market under the branded names of Prozac®, Prozac® Weekly, Rapiflux®, Sarafem®, and Selfemra®.

What is Fluoxetine, And Why Is It Used?

Fluoxetine is a medication from the group of Selective Serotonin Reuptake Inhibitors (SSRI). It is approved for treating major depressive disorder (in patients eight years of age and older), obsessive-compulsive disorder, panic disorder, bulimia, binge eating disorder, premenstrual dysphoric disorder, and bipolar depression, as well as treatment-resistant depression when combined with olanzapine. (1)

How Does Fluoxetine Work?

Fluoxetine increases the serotonin levels in the body, primarily in the brain. In this way, fluoxetine may increase the effects of serotonin, including improved mood and alertness. It has been seen that some mental health disorders, such as depression, are linked with low levels of serotonin and norepinephrine in the brain. (2)

Important Information

Read the box label information and address your inquiries about your medication with your doctor and pharmacist. Ask for additional information on how to use the medication safely. They can guide you through the treatment.

Box Warning: Increased Risk Of Suicidality

Children, adolescents, and young adults of less than 24 years taking antidepressants like fluoxetine were more likely to experience abnormal behavior leading to increased suicidal thoughts and behavior.

The changes in thinking and behavior were seen in short-term studies of patients with Major Depressive Disorder and other mental conditions. Additionally, these side effects were more common at the start of the therapy. Doctors are unsure if this side effect results from the underlying condition, the medication, or both. (3)

However, if you or someone you care present the following warning signs: (4)

  • Talking or thinking about wanting to die, unexplained guilt or shame, or being a burden to other people;
  • Feeling sad, abnormally anxious, agitated, empty, hopeless, without reason to live, abnormally angry, or in unsupportable pain;
  • Abnormal behavior, including looking for ways to die, isolating from friends or loved ones, saying goodbye, giving away important items, taking extreme risks, having abrupt mood swings, abnormal sleeping or eating, or increased use of alcohol or drugs;

Contact your doctor immediately or go to the nearest hospital right away. Seek help from your relative(s), caregiver(s), or friend(s) in case you are not able to do it on your own.

Fluoxetine is not approved for children under seven years of age.

Common Side Effects of Fluoxetine

The Side Effects Of Fluoxetine

Common Side Effects Of Fluoxetine

How Common Are Common Side Effects?

In the studies on fluoxetine, common side effects appeared in more than 1 out of 100 people. In the following section, you’ll learn more about the common side effects of fluoxetine. (3)

List Of Common Fluoxetine Side Effects:

  • Anxiety;
  • Nervousness;
  • Skin rash;
  • Difficulty falling asleep;
  • Nausea;
  • Headache;
  • Feeling tired;
  • Watery, loose, and/or increased amount of stools;
  • Decreased or lack of appetite;
  • Dry mouth;
  • Indigestion;
  • Hard and difficult to pass, and/or decreased amount of stools;
  • Increased frequency of passing gas;
  • Vomiting;
  • Weight loss;
  • Sleepiness;
  • Dizziness, instability, or feeling lightheaded;
  • Shaky body parts or whole body;
  • Decreased sexual interest or desire;
  • Abnormal or unusual thinking;
  • Yawn;
  • Abnormal sweating;
  • Itching;
  • Abnormal vision.

Less Common And Rare Side Effects Of Fluoxetine

How Common Are Less Common And Rare Side Effects?

As for the common side effects, less common and rare side effects were experienced by people in fluoxetine clinical trials. Less common side effects were seen in 1 in 1000 to 1 in 100 people. Rare side effects appeared in less than 1 in 1000 participants. (3)

List Of Less Common Fluoxetine Side Effects:

  • Thoughts of self-harm, including the risk of suicidal feelings or actions (see Box Warning);
  • Abnormal heart beating;
  • Feeling lightheaded or fainting due to decreased blood pressure;
  • Heartburn or stomach pain;
  • Gut inflammation or infection;
  • Black stools;
  • A sore on the inner lining of the stomach;
  • Easy bruising;
  • Abnormal and uncontrolled body movements;
  • Impaired movement coordination;
  • Loss of balance when walking or standing;
  • Abnormal teeth grinding during sleep;
  • Abnormal and uncontrolled movements of the tongue and mouth;
  • Feeling detached from self;
  • Intense or unexplained happiness or excitement;
  • Hard muscles leading to difficulty in moving or abnormal postures;
  • Jerky limb or body movements;
  • Feeling discomfort with or distrust of other people;
  • Abnormal hair loss;
  • Dilated pupils;
  • Abnormal uterine bleeding.

List Of Rare Fluoxetine Side Effects:

  • Severe and constant stomach pain, feeling sick, and vomiting;
  • Blood in stools;
  • Bloody vomiting;
  • Pain in the upper right side of your belly, yellowing of the skin and white part of the eyes, dark urine, and white or grayish stools.
  • Sore(s) on the lining of the stomach or duodenum (first part of the gut) leading to pain before or after eating;
  • Red or purple spots on the skin and/or the inner lining of the mouth or eyelids;
    Abnormal and unreal beliefs;
  • Throat swelling.

Warnings And Precautions: Severe Adverse Reactions Of Fluoxetine

This section explains the possible severe adverse reactions while taking fluoxetine. You will notice that some of these are listed in the previous sections because some can be mild, while others can be severe.

For complete information, it is highly recommended to read the patient information in the box of your prescription medicine (3). Additionally, talk to your doctor and pharmacist to learn more about side effects.

Call the emergency and/or seek immediate medical attention if you notice any signs or symptoms of severe adverse reactions.

Allergic Reactions

Some people may be hypersensitive to fluoxetine or any of the other ingredients of the medication. Hypersensitivity consists of an exaggerated immune or allergic response to fluoxetine or any other ingredients.

Allergic reactions may manifest as skin rash, itching, watery stools, stomach pain, skin swelling, face, mouth, tongue, or throat, difficulty breathing, and/or lightheadedness or fainting due to low blood pressure. While some people present mild allergic symptoms, others may have severe and life-threatening allergic reactions. (3)


In some patients, the action of fluoxetine may not be as well tolerated as in others. In these people, it is seen that there is elevated anxiety and agitation. These side effects might not be even under people’s control. It is essential to seek help from a doctor to manage these side effects effectively. (5)

To avoid such a situation, it is best if the patient notifies their doctor about any feelings of anxiety before or when taking fluoxetine.

Serotonin Syndrome

In people taking fluoxetine, there is an increased risk of serotonin syndrome. It is characterized by mental fogginess, altered thoughts or perception, losing consciousness, increased sweating, vomiting, loose or watery stools, increased body temperature, red and hot skin, dry mouth, dilated pupils, and abnormal body movements.

Serotonin syndrome occurs due to increased levels or effects of serotonin in the body. This is more common in people taking other medications that increase serotonin levels or effects. Some examples are citalopram, escitalopram, sertraline, duloxetine, paroxetine, tramadol, imipramine, amitriptyline, clomipramine, trazodone, bupropion, and lithium. However, it can also occur in people taking fluoxetine alone. (6)

Induction Of Mania

Although rarely seen, the induction of mania is often noticed in younger individuals who are started on fluoxetine. People who might also develop unnoticed bipolar disorder are seen to increase their risk of a manic episode. (7)

A manic episode is characterized by elevated mood, feelings of grandiosity, increased energy and impulsivity, and decreased need for sleep.

Increased Risk Of Suicidality

Similarly, suicidal thoughts or behavior were also seen to develop in some patients taking fluoxetine (see Box Warning). Therefore, knowing and understanding the danger signs and how they can be avoided is essential. (8)


Prozac is also linked with sleep deprivation, also known as insomnia. The reason behind its occurrence is the elevation of serotonin levels in the brain. (9)

Although serotonin helps regulate mood and, thus, helps prevent depression and other mood disorders, it is also seen to alert the mind and make it stay active. This ultimately leads to insomnia, worsening anxiety, and other mood symptoms.

Sexual Dysfunction

In many of the patients, both males and females, certain disorders linked with sexual reproductive functioning were seen. These side effects may occur when taking fluoxetine: anorgasmia (difficulty reaching orgasm), decreased sex drive, and ejaculatory problems. (10)

In rare cases, fluoxetine therapy may produce long-lasting (more than two hrs.) and painful erections in men (11). This side effect, called priapism, can occur without sexual stimulation. Moreover, priapism can damage the penis, requiring immediate medical attention.


People taking fluoxetine can experience a seizure or fit, especially if they have a seizure disorder (epilepsy). Seizures can produce abnormal jerky movements in the limbs and body. Some people may lose consciousness while experiencing a seizure. This condition can be life-threatening in some people, mainly producing difficulty in breathing. (12)

If a person is affected by a seizure, they should be left lying on the ground on their side, protecting them from sharp elements, fire or hot fluids, or baths and pools. It is not advisable to introduce any element into the mouth of the person. Seek help by calling the emergency services right away.

What To Do In Case Of Side Effects?

If you or someone you care for develops any of the side effects, address the abnormal feeling, sensation, or manifestation, and promptly communicate with your doctor; they can assess the severity and the need for appropriate care.

Call the emergency services or go to the nearest hospital or healthcare facility if severe side effects appear.

You may also help doctors and health authorities by reporting side effects to FDA at 1-800-FDA-1088 or

Final Remarks

Despite side effects, fluoxetine is an FDA-approved medication and a valuable option for patients with major depressive disorder and other mental and mood disorders (13). However, it is essential to emphasize that it should be used under the prescription and supervision of a licensed healthcare practitioner, as the effectiveness may vary based on each person’s individual response.


Can I Take Fluoxetine If I Breastfeed My Infant?

Fluoxetine is not recommended in pregnant, lactating, and breastfeeding mothers. It gets secreted in the breast milk and could be passed to the baby, thus posing risks to their health. Always check the medication label when starting a new medication. (14)

How Does Fluoxetine Act On My Brain?

Fluoxetine exerts its effects by increasing the levels of serotonin – the “feel good and happy” chemical in the brain. Once there are normal to slightly increased serotonin levels in the brain, the person might improve the symptoms of their condition.

Is Fluoxetine Safe Enough To Be Taken Daily?

Certainly! It is generally recommended to consult with a doctor to determine the appropriate dosage of fluoxetine based on the specific symptoms. However, the usual daily dose is often considered safe and sufficient to achieve the desired effects. However, the impact on patients varies; therefore, your doctor could guide you better regarding your condition.

Can Fluoxetine Affect My Eyes Too?

In rare cases, using fluoxetine has been associated with blurred vision and the development of angle-closure glaucoma (severely painful red eye). In these cases, you should seek medical attention promptly. (15)

Can People With Kidney Or Liver Problems Take Fluoxetine?

People with kidney or liver problems may receive a dose adjusted to their kidney or liver function. These organs are responsible for breaking down and removing drugs from the body. Consequently, doctors can safely change the therapy according to the person’s condition.

Can Fluoxetine Make You Gain Weight?

Although some weight gain can be seen at the start of the therapy, this is usually not significant. Moreover, other factors, such as previous weight or dietary habits, might influence body weight. (16)

See Also

How to Get Prescribed Anxiety Medication?

Bupropion Side Effects When Treating Depression?

Bupropion Interactions

Sertraline Interactions

Tramadol Interactions

Current Version
August 10, 2023
Medically Reviewed By
Franco Cuevas, MD
August 9, 2023
Written By
Andleeb Asghar, PharmD
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