Fluoxetine (Prozac): What it is, How it Works, Uses & More

Kristin Hall

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 7/19/2020

Fluoxetine, sold under the brand name Prozac®, is an antidepressant prescribed to treat depression, as well as several other conditions. 

Fluoxetine belongs to a class of medications called selective serotonin reuptake inhibitors, or SSRIs. These medications adjust the level of certain chemicals in your brain to improve your mood and treat the symptoms of depression. 

In addition to depression, fluoxetine is prescribed to panic disorder and obsessive-compulsive disorder (OCD). It’s also used as a treatment for premenstrual dysphoric disorder and certain eating disorders, such as bulimia. 

If you’ve been diagnosed with depression, your healthcare provider may recommend fluoxetine as the best treatment option.

Like other antidepressants, fluoxetine has advantages and disadvantages, including a range of potential side effects.

Below, we’ve explained what fluoxetine is, how it works, its common side effects and more. We’ve also answered some of the most common questions about fluoxetine.

What is Fluoxetine (Prozac)?

Fluoxetine is an antidepressant medication. It belongs to a class of medications referred to as selective serotonin reuptake inhibitors, or SSRIs. 

Fluoxetine is one of the most widely-used prescription medications in the United States, tens of millions of prescriptions written for it every year. 

The most common use for fluoxetine is as a treatment for depression. Fluoxetine is also used to treat premenstrual dysphoric disorder (PMDD, severe depression, irritability and tension prior to menstruation)obsessive-compulsive disorder, and panic disorder bulimia nervosa.

While not approved by the FDA to treat it, there are numerous studies out there that indicate it may be an effective treatment for post-traumatic stress disorder (PTSD), anxiety and certain eating disorders

First approved in the late 1980s, fluoxetine is less likely to cause certain side effects than many of the older medications used to treat depression, such as tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs).

You may have already heard of fluoxetine by its original brand name, Prozac. Today, fluoxetine is available as a generic medication under a range of different brand names.

How Fluoxetine Works

Fluoxetine works similarly to other SSRIs, by changing the level of certain chemicals, referred to as neurotransmitters, in your brain.

Neurotransmitters are chemicals that are used by your brain to send important signals between neurons. Your brain uses neurotransmitters to control a range of biological functions, from your heart rate to your sleep-wake cycle, breathing patterns, appetite, mood and more.

Fluoxetine and other SSRIs work by changing the way your brain manages a neurotransmitter called serotonin.

Serotonin is known to some as the “feel good” neurotransmitter. It’s responsible for a variety of functions in your body, including regulating your mood, happiness, sleep patterns, anxiety, appetite, social behavior and sexual function.

Although the exact relationship between serotonin and depression isn’t fully known, people with depression and certain anxiety disorders often have low levels of serotonin and weak serotonin transmission.

Fluoxetine works by stopping your brain from reabsorbing serotonin. 

By doing this, it increases the amount of serotonin that’s circulating at any one time and, if effective, improving your mood and treating the symptoms of depression. 

Fluoxetine Dosages

Fluoxetine comes as a tablet, capsule and liquid solution. Fluoxetine capsules are available in two different forms — standard-release and delayed-release. 

For depression, fluoxetine is typically prescribed at an initial dosage of 20mg per day. This may be adjusted to a regular dosage of 20mg to 60mg per day, depending on your symptoms, response to the medication, general health and other factors. 

The maximum dosage of fluoxetine used to treat depression is 80mg per day. In some cases, a delayed-release form of fluoxetine may be prescribed at a higher dosage. 

Fluoxetine may be prescribed for use with other medications. Follow the instructions provided by your healthcare provider and only use fluoxetine as prescribed. Do not adjust your fluoxetine dosage or stop using this medication without talking to your healthcare provider. 

Related read: Can You Overdose on Prozac?

Fluoxetine Side Effects and Interactions

Fluoxetine may cause a range of side effects. Many of these side effects are common to SSRI medications. The most common side effects of fluoxetine are often temporary and may pass on their own over the course of several weeks.

Like other antidepressants, fluoxetine may also cause serious side effects, including potentially hazardous side effects that you should be aware of before using this medication.

Common side effects of fluoxetine (affecting more than five percent of users) include:

  • Abnormal dreams

  • Anorexia

  • Anxiety

  • Decreased libido (reduced interest in sex)

  • Diarrhea

  • Dizziness

  • Dry mouth

  • Dyspepsia (indigestion)

  • Fatigue

  • Flu-like syndrome/symptoms

  • Headache

  • Insomnia

  • Nausea

  • Nervousness

  • Pharyngitis (sore throat)

  • Rash

  • Rhinitis (hay fever)

  • Sinusitis

  • Somnolence (drowsiness)

  • Sweating

  • Tremor

  • Vasodilation

  • Yawning

Fluoxetine may cause other common side effects in addition to those listed above. If you have concerns about side effects, you should discuss these with your healthcare provider before using fluoxetine and/or other medications to treat depression. 

Several SSRIs, including fluoxetine, can cause sexual side effects. In clinical trials, four percent of people given fluoxetine reported a decreased level of interest in sex. 

In women, fluoxetine may cause other sexual side effects, including difficulty or inability to reach orgasm. 

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FDA “Black Box” Warning: Suicidal Thoughts and/or Behavior

The FDA mandates that antidepressants, including fluoxetine, are sold with a “black box” safety warning notifying users of potentially serious side effects.

These side effects include an increased risk of suicidal thoughts and/or behavior in children and young adults prescribed antidepressants. This risk is highest during the first weeks and months of treatment and affects people below the age of twenty-four.

If you’re prescribed fluoxetine or any other antidepressant with this FDA warning, contact your healthcare provider immediately if you experience any unusual thought patterns, sudden changes in mood or suicidal thoughts and/or feelings.

Interactions Between Fluoxetine and Other Medications

Fluoxetine can interact with other medications, including common prescription drugs and some over-the-counter medications, supplements and herbal products. These interactions can make fluoxetine more or less effective and, in some cases, cause serious health issues.

You should not use fluoxetine if you have used any monoamine oxidase inhibitors (MAOIs) in the last 14 days. MAOIs are a type of medication prescribed to treat depression. Widely-used MAOIs include phenelzine, isocarboxazid, tranylcypromine, selegiline and others. 

These medications can interact and cause serious, life-threatening side effects including rapid changes in blood pressure and heart rate, muscle spasms, high fever and loss of consciousness.

You should also not use fluoxetine with the antipsychotic medications thioridazine or pimozide. These medications can cause severe and potentially deadly heart rhythm problems when used with fluoxetine. 

Fluoxetine may also interact with other medications, causing an increased risk of experiencing certain side effects. You should not use fluoxetine with:

  • Other antidepressants, including SSRIs, SNRIs and tricyclic antidepressants (TCAs)

  • Opioid painkillers, such as tramadol and fentanyl

  • Nonsteroidal anti-inflammatory drugs (NSAIDs)

  • Any medications broken down by the CYP2D6 enzyme

  • Amphetamines

  • Certain anticonvulsants, such as carbamazepine

  • Some anti-epileptic medications, such as phenytoin

  • Buspirone

  • Aspirin

  • Lithium

  • Benzodiazepines

  • Triptans

  • Tryptophan

  • St. John’s wort

  • Warfarin

To avoid any potentially hazardous drug interactions, inform your healthcare provider of all prescription and over-the-counter medications that you either currently use or have recently used before talking about fluoxetine. 

To learn about another potential interaction, read our article on Prozac and weed.

Fluoxetine and Pregnancy

Fluoxetine has a category C rating from the FDA. This means that animal studies of fluoxetine have shown that it may have certain adverse effects for the fetus when used during pregnancy, but that adequate studies haven’t been carried out in humans to assess its pregnancy risk. 

If you use fluoxetine and believe that you’re pregnant, or plan to become pregnant, contact your healthcare provider. You should not stop taking fluoxetine or adjust your dosage before talking to your healthcare provider. 

Like many other antidepressants, fluoxetine can pass into breast milk in small amounts. If you’re currently breastfeeding or plan to breastfeed your child and currently use fluoxetine, talk to your healthcare provider for assistance. 

Our blog answers Is It Safe To Take Prozac® While Pregnant? in more detail.

Learn More About Medications for Treating Depression

If you have depression, a wide range of options are available to treat your symptoms and help you recover. 

Fluoxetine is one of the most common medications used to treat depression. However, it’s not the only option available. Depending on your symptoms, history of depression, general health and other factors, your healthcare provider may recommend fluoxetine or a different medication.

Our guide to medications for depression goes into more detail about the medications that are available to treat depression, from how they work to the advantages, disadvantages and side effects of each option. 

Frequently Asked Questions About Fluoxetine (Prozac®)

How and When Should You Take Fluoxetine (Prozac®)?

You can take fluoxetine at any time of day. It’s best to take fluoxetine at roughly the same time every day to make sure the medicine is properly absorbed by your body. Fluoxetine is okay to take on its own or with food.

Some people experience insomnia after starting treatment with fluoxetine. If you find it difficult to fall asleep, try taking fluoxetine early in the morning, shortly after you wake up. 

If you forget to take fluoxetine and miss a dose, take the missed dose as soon as possible. If it’s already the next day, don’t take a double dose of fluoxetine — instead, skip the missed dose and continue using the medication as normal. 

If you accidentally take too much fluoxetine and experience side effects such as vomiting, a fast heartbeat, dizziness, agitation, tremors or nausea, call 911 for emergency assistance. 

Fluoxetine may be prescribed at a different dosage for non-depression conditions. If your healthcare provider has prescribed fluoxetine, carefully check and follow the usage instructions provided with your medication. 

How Long Does it Take for Fluoxetine (Prozac®) to Work?

Fluoxetine can take several weeks to start working as a treatment for depression. What does prozac feel like when it starts working? It’s normal to experience improvements in your energy levels, sleep and appetite in the first one to two weeks of treatment with fluoxetine.

The full effects of fluoxetine, such as improved mood and interest in certain activities, may take six to eight weeks to occur. 

If you’ve already used fluoxetine for several weeks but haven’t experienced any improvements, do not stop taking this medication without first contacting your healthcare provider. Based on your symptoms and response to treatment, your healthcare provider may suggest a different dosage or a new medication. 

How Long Does Fluoxetine (Prozac®) Stay in Your System?

Compared to other antidepressants, fluoxetine has a very long half-life. It’s also unique in that its metabolism is inhibited by its metabolite, norfluoxetine, meaning it typically takes longer for fluoxetine to exit your system the longer you have been using the medication. 

In most people, it takes between one and three days for one dose of fluoxetine to reach half of its original concentration in the body. 

If fluoxetine has been used for the long term, it may take four to six days for the medication to reach half of its original concentration in the body. Following long-term use, it takes around 25 days of non-use for 99 percent of fluoxetine to exit your body. 

How Should You Stop Taking Fluoxetine (Prozac®)?

Fluoxetine’s long half-life means it may be less likely to cause withdrawal symptoms than other antidepressants.

However, you should not stop using fluoxetine without first consulting your healthcare provider. If you’ve used fluoxetine over the long term, stopping without tapering your dosage could increase your risk of experiencing symptoms such dizziness, headaches, shaking, anxiety or difficulty sleeping.

If you’d like to stop using fluoxetine, talk to your healthcare provider before adjusting your dosage or stopping use of this medication. Your healthcare provider will likely recommend gradually tapering your dosage, which will reduce your risk of experiencing withdrawal symptoms.

Does Fluoxetine Interact With Birth Control?

Fluoxetine does not interact with any forms of hormonal birth control, meaning you can use the pill, patch or other contraceptives. You can also use the morning-after pill and other emergency contraceptives while using fluoxetine. 

Although there’s no interaction between fluoxetine and birth control, it’s important to inform your healthcare provider about all medications you currently use while discussing fluoxetine. 

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Can You Drink Alcohol While Using Fluoxetine? 

It’s best to avoid drinking alcohol while you’re using fluoxetine. Consuming alcohol can increase your risk of experiencing side effects from both fluoxetine and alcohol, including effects such as drowsiness, loss of coordination, impaired judgment and slower reaction time. 

If you frequently drink alcohol or have alcohol dependence, make sure that you discuss this with your healthcare provider before getting a prescription for fluoxetine online.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.

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