Fluoxetine Interactions, Side Effects, and Warnings

Prozac, Paxil and Zoloft anti-depressant tablets, close-up

Jonathan Nourok / The Image Bank / Getty Images

Prozac is the brand name of the drug fluoxetine, a selective serotonin reuptake inhibitor (SSRI). SSRIs are second-generation antidepressants, which means they are newer than first-generation medications such as monoamine oxidase inhibitors (MAOIs) or tricyclic antidepressants (TCAs).

Because serotonin is involved in the regulation of anxiety as well as mood, clinicians sometimes prescribe SSRIs for phobia treatment, particularly social phobia. Fluoxetine may relieve symptoms of anxiety, but it is also important to be aware of the potential drug interactions, side effects, and warnings before taking this medication.

Serotonin Basics

Serotonin is a neurotransmitter, a chemical that carries signals between neurons in the brain. SSRIs, including fluoxetine, slow the rate at which the brain reabsorbs serotonin, allowing it to spend more time in the space between neurons, known as the synaptic gap.

This allows the serotonin to transmit additional signals to the neurons. The effect of more serotonin in the brain is often to improve mood and reduce feelings of anxiety.

Fluoxetine may be most effective when it is utilized in combination with psychotherapy.

Taking Fluoxetine

Fluoxetine is available by prescription only and in a variety of strengths. Clinicians prescribe it for daily or weekly use. Although you may begin to feel better right away, fluoxetine often takes a while to work and need to be in your system over time.

Your doctor may start you on a low dose and gradually increase the amount you take until the desired results are achieved. The starting dose is typically 20 mg per day, which can then be increased as needed up to a maximum dose of 80 mg per day. Because it takes time for the medication to begin working effectively, it is important to keep taking your medicine and give it time to reach its full effects.

If you have questions or concerns, call your physician for instructions. Never attempt to adjust your dosage or medication schedule without professional guidance.

Fluoxetine Warnings

Fluoxetine is one of the only antidepressants approved for clinically depressed youths. However, there is some controversy surrounding its use. Speak to your doctor, or your child's doctor, about the risks and benefits of fluoxetine in order to make an informed decision.

In 2004, the U.S. Food and Drug Administration began requiring all SSRIs, including fluoxetine, to carry a "black box" warning that stresses the increased risk for suicidality in children and adolescents. A black-box warning is the most stringent warning a drug can carry before the FDA pulls it from the shelves.

In 2007, the FDA ordered a review, expanded the directive to include anyone 24 years old or younger and added warnings to the black box about the higher risk of suicidality during the first 1 to 2 months of treatment.

If you are having suicidal thoughts, contact the National Suicide Prevention Lifeline at 988 for support and assistance from a trained counselor. If you or a loved one are in immediate danger, call 911.

For more mental health resources, see our National Helpline Database.

The review examined data from a group of more than 2,1000 children taking SSRI medications, about 4% experienced suicidal thoughts, including suicide attempts, but none of the children were successful at taking their own life. 

More recent reviews suggest that the benefits of antidepressant medications likely outweigh their potential risks to children and adolescents with major depression and anxiety disorders.

Fluoxetine Interactions

Before you begin taking fluoxetine, you should also tell your doctor about any medications or supplements you are currently taking. Some substances may interact with fluoxetine leading to potential adverse effects or impacting the actions of either medication.

Fluoxetine can interact with a long list of other medications. As a special precaution for fluoxetine, do not take it if you have taken any monoamine oxidase inhibitor (MAOI) within the past two weeks, and do not begin an MAOI within five weeks after discontinuing fluoxetine or any other SSRI.

Other medications that could interact with fluoxetine include:

  • A variety of mood disorder treatments
  • Migraine treatments
  • Seizure medications
  • NSAID pain relievers

Natural remedies such as St. John's wort also interact with fluoxetine and other SSRIs. They can lead to excessive serotonin levels in the brain, resulting in a condition known as serotonin syndrome.


Make sure your doctor is aware of all prescription, over-the-counter, and natural remedies you use. Always seek professional advice before taking anything new while taking fluoxetine. Avoid alcohol and sedatives.

Side Effects of Fluoxetine

Drowsiness or nervousness may occur, particularly when you first start taking fluoxetine. If you're having side effects from your medication, contact your doctor immediately. Avoid driving and operating heavy machinery until you know how you react to the medication

Fluoxetine can cause a variety of side effects, including, but not limited to:

  • Anxiety
  • Dry mouth
  • Excessive sweating
  • Fatigue
  • Headache
  • Nausea
  • Tremor
  • Sexual side effects
  • Sleep disturbances

In rare instances, people may experience severe anxiety, confusion, fever, vomiting, difficulty breathing, seizures, or hives. If you experience any of these symptoms while taking fluoxetine, you should contact your doctor immediately.

Frequently Asked Questions

  • What is fluoxetine used for?

    Fluoxetine is a type of selective serotonin reuptake inhibitor (SSRIs). It is FDA-approved to treat major depression panic diosrder, and obsessive compulsive disorder. However, it is also sometimes prescribed off-label to treat other conditions including other types of anxiety disorders.

  • How long does it take for fluoxetine to work?

    It takes time for fluoxetine to reach consistent levels in the body. People may begin to notice some effects in the first week or two, but it usually takes a few weeks before people begin to notice full effects.

  • What are the side effects of fluoxetine?

    Common side effects of fluoxetine include fatigue, sweating, dry mouth, sleep disturbances, nervousness, nausea, and headache. In many cases, these symptoms gradually abate as people become used to their medication.

7 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Bandelow B, Michaelis S, Wedekind D. Treatment of anxiety disordersDialogues Clin Neurosci. 2017;19(2):93-107. doi:10.31887/DCNS.2017.19.2/bbandelow

  2. Eli Lilly. Prozac medication guide.

  3. Grunebaum MF, Mann JJ. Safe use of SSRIs in young adults: how strong is evidence for new suicide warningCurr Psychiatr. 2007;6(11):nihpa81089.

  4. Jane Garland E, Kutcher S, Virani A, Elbe D. Update on the use of SSRIs and SNRIs with children and adolescents in clinical practiceJ Can Acad Child Adolesc Psychiatry. 2016;25(1):4-10.

  5. National Alliance on Mental Illness. Fluoxetine (Prozac).

  6. Food and Drug Administration. Highlights of prescribing information: Prozac.

  7. Foong AL, Grindrod KA, Patel T, Kellar J. Demystifying serotonin syndrome (or serotonin toxicity)Can Fam Physician. 2018;64(10):720-727.

By Lisa Fritscher
Lisa Fritscher is a freelance writer and editor with a deep interest in phobias and other mental health topics.