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What Are the Main Uses and Side Effects of Fluoxetine (Prozac, Fludac)?

Dr. Manura Nanayakkara is a practicing doctor in Sri Lanka. He holds a postgraduate diploma in psychiatry.

Fluoxetine affects chemicals in the brain that may become unbalanced and cause depression, panic, anxiety, or obsessive-compulsive symptoms.

Fluoxetine affects chemicals in the brain that may become unbalanced and cause depression, panic, anxiety, or obsessive-compulsive symptoms.

What Is Fluoxetine (aka Prozac or Fludac)?

Fluoxetine is an SSRI, or selective serotonin reuptake inhibitor class medication. It is mainly prescribed for clinical depression, anxiety disorders, and OCD (obsessive-compulsive disorders). Prozac is the original brand name of this drug, and Fludac is a popular brand in India. Its main side effects are insomnia and sexual dysfunction.

What does the drug do?

Fluoxetine inhibits serotonin reuptake in certain neuronal connections. This action increases the naturally occurring serotonin neurotransmitter levels. Increased serotonin levels cause changes in gene expression, which ultimately have a therapeutic effect. However, increased serotonin in unwanted areas of the brain can cause side effects.

In other words, it affects chemicals in the brain that may become unbalanced and cause depression, panic, anxiety, or obsessive-compulsive symptoms.

Uses of Medicines Containing Fluoxetine

Fluoxetine is prescribed as a first-line medication for clinical depression. In addition, it is prescribed to treat anxiety disorders such as generalized anxiety disorder, obsessive-compulsive disorder, premenstrual dysphoric syndrome (PMDD), as well as premature ejaculation.

Usually, drugs containing fluoxetine such as Prozac and Fludac are prescribed in the lowest possible dose which is increased until satisfactory symptom control is achieved. In the case of OCD, however, it is prescribed in slightly higher doses.

The usual dosage for depression is one 20 mg dose daily. However, unlike other antidepressants, an increased dose does not always mean a better response. Therefore, most psychiatrists switch to another antidepressant rather than increasing the amount of fluoxetine when the response is poor.

However, for conditions such as OCD, this medication is prescribed in the doses of 20 mg to 80 mg. In some cases, higher doses are sometimes prescribed in resistant patients.

How to Use Drugs Containing Fluoxetine

Fluoxetine can come as a capsule, a tablet, a delayed-release (releases the medication in the intestine) capsule, and a solution (liquid) to take by mouth. It can be taken with or without food though food can help prevent some gastric side effects.

Capsules, tablets, and liquids are usually taken once a day in the morning or twice a day in the morning and at noon. Fluoxetine delayed-release capsules are usually taken once a week.

General guidelines:

  • Take the medicine at around the same time(s) every day.
  • Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand.
  • Take fluoxetine exactly as directed. Do not take more or less of it, or take it more often than prescribed by your doctor.

When you first start treatment:

Your doctor may start you on a low dose of fluoxetine and gradually increase your dose.

It may take four to five weeks or longer before you feel the full benefit of fluoxetine. Continue to take fluoxetine even if you feel well.

Do not stop taking fluoxetine without talking to your doctor. If you suddenly stop taking fluoxetine, you may experience withdrawal symptoms such as mood changes, irritability, agitation, dizziness, numbness or tingling in the hands or feet, anxiety, confusion, headache, tiredness, and difficulty falling asleep or staying asleep. Your doctor will probably decrease your dose gradually.

Important Warnings for Using Fluoxetine

A small number of children, teenagers, and young adults (up to 24 years of age) who took antidepressants or "mood elevators" such as fluoxetine during clinical studies became suicidal.

Children, teenagers, and young adults who take antidepressants to treat depression or other mental illnesses may be more likely to become suicidal than children, teenagers, and young adults who do not take antidepressants to treat these conditions.

However, experts are not sure how great the risk is and how much it should be considered in deciding whether a child or teenager should take an antidepressant.

Other Mental Health Concerns

You should know that your mental health may change in unexpected ways when you take fluoxetine or other antidepressants even if you are an adult over 24 years of age.

You may become suicidal, especially at the beginning of your treatment and any time that your dose is increased or decreased.

You, your family, or your caregiver should call your doctor right away if you experience any of the following symptoms:

  • New or worsening depression
  • Thinking about harming or killing yourself, or planning or trying to do so
  • Extreme worry
  • Agitation
  • Panic attacks
  • Difficulty falling asleep or staying asleep
  • Aggressive behavior
  • Irritability
  • Acting without thinking
  • Severe restlessness
  • Frenzied abnormal excitement

Be sure that your family or caregiver knows which symptoms may be serious so they can call the doctor if you are unable to seek treatment on your own.

Your healthcare provider will want to see you often while you are taking fluoxetine, especially at the beginning of your treatment. Be sure to keep all appointments for office visits with your doctor.

No matter your age, before you take an antidepressant, you, your parent, or your caregiver should talk to your doctor about the risks and benefits of treating your condition with an antidepressant or with other treatments.

You should also talk about the risks and benefits of not treating your condition. You should know that having depression or another mental illness greatly increases the risk that you will become suicidal.

This risk is higher if you or anyone in your family has or has ever had bipolar disorder (mood that changes from depression to mania, a frenzied, abnormally excited mood) or has thought about or attempted suicide.

Talk to your doctor about your condition, symptoms, and personal and family medical history. You and your doctor will decide what type of treatment is right for you.

Consult Your Doctor

As with every medication, there are important precautions that you need to take into consideration before starting treatment. Make sure your doctor has your detailed medical history. Call your doctor right away if you experience any of of the serious side effects listed above.

Before You Take Prozac or Fludac

As with every medication, there are important precautions that you need to take into consideration before starting treatment and make sure your doctor has your detailed medical history.

Before you take Prozac or Fludac, be sure you:

  • Tell your doctor and pharmacist if you are allergic to fluoxetine or any other medications.
  • Tell your doctor if you are taking pimozide (Orap), thioridazine, or monoamine oxidase (MAO) inhibitors such as isocarboxazid (Marplan), phenelzine (Nardil), selegiline (Eldepryl, Emsam, Zelapar), and tranylcypromine (Parnate).
  • If you have stopped taking a monoamine oxidase inhibitor within the past two weeks. Your doctor will probably tell you that you should not take fluoxetine. If you stop taking fluoxetine, you should wait at least five weeks before you begin to take thioridazine or a monoamine oxidase inhibitor.
  • Tell your doctor and pharmacist what other prescription and nonprescription medications and vitamins you are taking or plan to take since these can affect your reaction to Prozac or Fludac.
  • Tell your doctor what nutritional supplements and herbal products you are taking, especially products that contain St. John's wort or tryptophan.
  • Tell your doctor if you are being treated with electroshock therapy, if you have recently had a heart attack, and if you have or have ever had diabetes, seizures, or liver or heart disease.
  • Tell your doctor if you are pregnant, especially if you are in the last few months of your pregnancy, or if you plan to become pregnant or are breastfeeding.
  • If you become pregnant while taking fluoxetine, call your doctor. Fluoxetine may cause problems in newborns following delivery if it is taken during the last months of pregnancy.
  • Talk to your doctor about the risks and benefits of taking fluoxetine on a daily basis if you are 65 years of age or older. Older adults should usually take fluoxetine on a daily basis because it is not as safe as other medications that can be used to treat the same conditions.

Other Information You Should Know Before You Start Treatment:

  • You should know that fluoxetine may make you drowsy. Do not drive a car or operate machinery until you know how this medication affects you.
  • Remember that alcohol can add to the drowsiness caused by this medication.
  • You should know that fluoxetine may cause angle-closure glaucoma (a condition where the fluid is suddenly blocked and unable to flow out of the eye causing a quick, severe increase in eye pressure which may lead to a loss of vision).
  • Talk to your doctor about having an eye examination before you start taking this medication. If you have nausea, eye pain, or changes in vision (such as seeing colored rings around lights,) call your doctor or get emergency medical treatment right away.

Most Common Side Effects for Patients Just Starting to Use Fluoxetine

This medication can cause an initial aggravation of anxiety. For this reason, some patients with anxiety stop taking it after the first couple of weeks. However, this initial anxiety settles with time, usually within about two weeks.

This medication can cause also tremors at the beginning which go away over time.

Gastric discomfort

Other significant side effects are gastric discomfort, nausea, and vomiting. Therefore, this medication should be taken with meals. Do not take it first thing in the morning. If the gastric side effects are severe, you might need to take medications that will stop them such as Omeprazole 20 mg twice daily or Domeperidone 10 mg tds.

Sleep disturbance or insomnia

Fluoxetine is also known to cause disturbance of sleep or insomnia. Therefore, it is prescribed to be taken in the morning. It should not be taken at night.

Sexual dysfunction

Drugs containing fluoxetine can cause sexual dysfunction, including lack of desire or libido and male erectile impotence. In fact, some studies have confirmed that around 80% of patients who take drugs containing fluoxetine experience some form of sexual dysfunction.

At the same time, however, clinical depression is also known to cause sexual dysfunction. The net effect of the treatment will depend on the individual.

Allergic reactions

Some patients can get allergic reactions such as anaphylaxis with this drug. It can also cause rashes.

Other physical symptoms

In addition, some patients can get tremors, headaches, dizziness, increased sweating, and short-term increase in anxiety.

What are the rare side effects of fluoxetine?

On more rare occasions, fluoxetine can also cause:

  • Problems with blood sugar control in patients with diabetes
  • Pharyngitis
  • Fainting as a result of low blood pressure
  • Increased risk of fits or seizures as a result of changes in electrolyte levels
  • Mania in patients with bipolar disorder

Other Documented Side Effects

Fluoxetine can have different side effects in different people. Tell your doctor if any of these symptoms are severe or do not go away:

  • Nervousness
  • Nausea
  • Dry mouth
  • Sore throat
  • Drowsiness
  • Weakness
  • Uncontrollable shaking of a part of the body
  • Loss of appetite
  • Weight loss
  • Changes in sex drive or ability

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:

  • Rash
  • Hives
  • Joint pain
  • Swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs
  • Difficulty breathing or swallowing
  • Fever, sweating, confusion, fast or irregular heartbeat, and severe muscle stiffness
  • Seeing things or hearing voices that do not exist (hallucinating)
  • Seizures

Fluoxetine may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.


Apeksha on June 05, 2017:

My father taking fludac 10 from last 15 yrs wht i do it couses any big his life due to this.... or death something. ....plz plz plz suggest me abt that...plz

Kim Harris on January 31, 2012:

good info about prozac, njmanura. Thanks.