Prozac (Fluoxetine)

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What is Prozac (fluoxetine)?

Prozac is a medication that belongs to the class of antidepressants called selective serotonin reuptake inhibitors (SSRIs).

Prozac works by blocking the brain's ability to reabsorb naturally occurring serotonin. Serotonin, a neurotransmitter, helps regulate mood by supporting brain function and regulating communication between brain cells. Prozac helps the brain maintain a sufficient level of serotonin.

Prozac (fluoxetine) is used to treat depression, obsessive-compulsive disorder, and panic disorder in adults. It may also be used for other conditions as determined by your doctor.

How does Prozac work?

Prozac belongs to a group of medications called selective serotonin reuptake inhibitors, or SSRIs. These drugs work by increasing the amount of serotonin available at synapses (nerve endings where messages from one neuron connect with another). This means that messages can be passed along more effectively.

The drug does not change how neurons function. Instead, it changes the way neurons communicate with each other.

What is serotonin?

Serotonin is a chemical messenger naturally produced by the body. It plays an important role in maintaining healthy mental function. When there is enough serotonin, you might feel happy, energetic, optimistic, calm, relaxed, and content. When there is too little serotonin, you might feel depressed, anxious, sad, angry, irritable, agitated, restless, guilty, hopeless, helpless, worthless, and guilty.

Serotonin is found throughout the central nervous system, including the brain stem, spinal cord, and peripheral nerves. It is primarily located in the limbic system in the brain which controls emotions such as fear, anxiety, aggression, sexual desire, and pleasure.

When released into the synaptic cleft (the space between neurons), serotonin binds to receptors on neighboring cells causing them to release more serotonin. The process continues until all the serotonin receptors have been activated. Once this occurs, the cell releases a second signal that tells the brain to stop producing serotonin.

Prozac increases the amount of serotonin in your brain, so you may experience fewer symptoms of depression when you take it.

What happens if you don’t have enough serotonin?

If there is not enough serotonin in your brain, you might experience symptoms of depression. Symptoms include:

  • Fatigue

  • Sleep disturbance

  • Feelings of worthlessness

  • Loss of appetite

  • Low energy

  • Difficulty concentrating

  • Poor memory

  • Irritability

  • Anxiety

  • Agitation

  • Restlessness

  • Suicidal thoughts

What causes a lack of serotonin in the brain?

You could develop a serotonin deficiency for the following reasons:

  • Stressful life events

  • Trauma

  • Illness

  • Medications

  • Genetics

  • Hormonal imbalances

  • Environmental toxins

  • Alcohol abuse

  • Drug use

  • Other medical problems

Seeing results

If you respond well to Prozac,¹ you may notice an improvement in your anxiety symptoms and feel more like yourself again.

You might feel relaxed, worry-free, energized, more focused, and you might have an improved sleeping pattern and feel less tired. Having a better appetite is another sign that Prozac is working.

Prozac can help relieve depression symptoms within two to four weeks; however, it may take up to 12 weeks for any positive changes to take effect.

How to take Prozac

Take Prozac exactly as prescribed by your doctor. Check the label on the prescription bottle for instructions and follow the directions carefully.

Do not take more than what was prescribed. If you do not understand any part of the usage instructions, consult your doctor or pharmacist.

Prozac is normally taken once a day, but depending on your condition, your doctor may tell you to take it twice a day.

If you're taking Prozac to treat premenstrual syndrome, your doctor may suggest you take it every day throughout the entire month or for the two weeks leading up to your period until the first day of your period.

What are the recommended doses of Prozac?

Your doctor will prescribe a dosage based on your medical condition and response to treatment. Your doctor may prescribe Prozac at a low dose and then gradually increase it.

Follow your doctor's advice carefully and keep taking the medication until you are advised to stop. Try to take Prozac at the exact same time each day so you’re not as likely to forget a dose.

Adult daily dose range: 10–20mg

Children's daily dose range: 10–15mg

Maximum daily dose: 40mg

What to discuss with your doctor before taking Prozac

Tell your doctor if:

  • You are allergic to fluoxetine, any of the ingredients in fluoxetine, or any other type of medication. Ask your pharmacist for a list of Prozac ingredients.

  • You have any medical conditions.

  • You're taking other medications or you've recently stopped taking medication. Your doctor may advise you not to take fluoxetine if it interferes with another medication.

  • You are taking any vitamins or supplements, including herbal products, as they may affect your medication. Your doctor may ask you to stop taking them before starting Prozac. Alternatively, your doctor will adjust your dose and monitor you carefully for adverse side effects.

  • You have recently had a heart attack or you or anyone else in your immediate family has ever had a long QT interval or irregular heartbeat.

  • You have ever had any of the following conditions: heart failure, bleeding problems, stroke, diabetes, seizures, or liver or kidney disease.

  • You plan to get pregnant, you're pregnant (especially if your pregnancy is in the later stages), or you’re breastfeeding. If you become pregnant while taking Prozac, contact your doctor immediately.

Prozac side effects

Nausea is the most common Prozac side effect, and it usually occurs within the first week of treatment.

Other possible Prozac side effects include:

  • Allergic reactions (symptoms include hives, skin rash, shortness of breath, wheezing, tightness in the chest, swelling of lips or tongue, or throat irritation)

  • Changes in menstruation

  • Dizziness, lightheadedness, faintness, or feeling tired or weak

  • Dry mouth, eyes, nose, or vagina

  • Feeling restless, agitated, angry, hostile, suspicious, guilty, depressed, anxious, confused, or paranoid

  • Headaches, stiff neck, backache, joint aches, or other body pains

  • Heartburn, indigestion, gas, bloating, cramps, or abdominal pain

  • Diarrhea or constipation

  • Insomnia, vivid dreams, nightmares, or sleepwalking

  • Itching, flushing, redness, or peeling skin

  • Poor coordination, slurred speech, or trouble walking or talking

  • Memory loss, lack of concentration, or poor judgment

  • Nervousness, restlessness, shakiness, or tremors

  • Painful urination or a frequent urge to urinate

  • Pain during sex

  • Swelling of hands, feet, ankles, eyelids, or lower legs

  • Tiredness, weakness, or fatigue

  • Vomiting that does not go away

  • Unexplained weight gain

  • Excessive thirst

  • Decreased interest in food

  • Yellowing of the skin or eyes

These side effects usually go away after several weeks of treatment. Some people may experience more serious side effects, including:

  • Suicidal thoughts or actions

  • Worsening of depression symptoms

  • Severe headaches

  • Abnormal heart rhythm

  • Changes in blood pressure

  • High or low blood sugar levels

  • Abnormal dreams

  • Nightmares

  • Panic attacks

  • Sudden hearing changes or ringing in the ears

When to see your doctor 

If you notice any new or unusual behaviors or thoughts when taking Prozac, speak to your doctor right away. These include:

  • Being nervous, anxious, irritable, aggressive, or violent

  • Agitation or hostility

  • Aggressive, inappropriate, or disruptive behavior

  • Mood disorder symptoms

  • Obsessive-compulsive behavior

  • Panic disorder symptoms

  • Paranoia

Long-term risks of Prozac

Prolonged use of Prozac may cause a condition called serotonin syndrome.² Symptoms of this disorder include:

  • Muscle stiffness

  • Sweating

  • Rapid heart rate

  • Confusion

  • Agitation

  • Hallucinations

  • Seizures

Seek medical help urgently if you have any of these symptoms as they could cause coma or death.

Missed doses of Prozac

If you miss a dose of Prozac, take it as soon as possible. If it’s almost time to take your next dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses.

If you miss doses, you may have an increased risk of relapsing.

Prozac storage

Store Prozac at room temperature between 59°F and 86°F (15–30°C). Store away from heat, moisture, and light. Keep Prozac out of the reach of children and away from pets.

Interactions with other drugs

Tell your doctor about any other medicines you use (prescribed or over-the-counter), including:

  • Other SSRIs

  • Serotonin and norepinephrine reuptake inhibitors (SNRIs)

  • Monoamine oxidase (MAO) inhibitors, such as isocarboxazid (Marplan), linezolid (Zyvox), methylene blue, phenelzine (Nardil), selegiline (Emsam, Zelapar), or tranylcypromine (Parnate)

  • Alprazolam (Xanax)

  • Amiodarone (Pacerone or Nexterone)

  • Certain antibiotics such as erythromycin (EES, Eryc, Ery-tab), gatifloxacin, moxifloxacin (Avelox), and sparfloxacin

  • Amphetamines (Adderall)

  • Dextroamphetamine (Dexedrine, Dextrostat, Adderall)

  • Methamphetamine (Desoxyn)

  • Anticoagulants (blood thinners) such as warfarin (Coumadin or Jantoven)

  • Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) 

  • Sedatives or sleeping pills

  • Pimozide (Orap)

  • Tranquilizers

  • Vinblastine

  • Thioridazine

You should also tell your doctor if you are taking medication for Parkinson's disease, mental illness, anxiety disorders, migraines, seizures, or diabetes.

Your doctor will likely advise against taking fluoxetine if you take any of the above medications; and if you stop taking fluoxetine, you should wait at least five weeks before you start taking thioridazine or a MAO inhibitor.

Do not stop using any medications without first talking to your doctor. Stopping certain medications before completing a full course of treatment may be harmful.

Who should not take Prozac

Prozac can pass from mother to baby during pregnancy and through breastmilk.³ If you're pregnant or breastfeeding, talk to your doctor before taking Prozac as the benefits may not outweigh the risks.

People over the age of 65 may face certain risks when taking Prozac.

The drug is safe and effective when used by adults, but it is not known whether it’s safe and effective for children younger than 18 years old.

Clinical trial history

The US Food and Drug Administration (FDA) approved Prozac for marketing based on results from two large clinical trials involving 1,000 patients with major depressive disorder. The first trial compared Prozac to a placebo, while the second trial compared Prozac to another antidepressant medication. In both studies, Prozac was found to be effective in treating major depressive disorders.

The FDA also approved Prozac for use by teenagers who suffer from a major depressive disorder.

1997 — The FDA approved Prozac for use in children aged six to 17 years old.

1998 — Prozac became available for use by pregnant women suffering from a major depressive disorder.

1999 — Prozac became available to treat postpartum depression, a condition that affects up to 20%⁴ of all mothers up to three months after delivery.

2000 — Prozac became available as a generic drug. Generic drugs are copies of branded drugs produced by other companies. They are sold under the same name but are less expensive.

2004 — Prozac became available with extended-release tablets. ‘Extended release’ means the tablet lasts longer in the stomach and intestines, making it easier for people to take the pill regularly.

  1. Prozac for anxiety disorders | Verywell Mind

  2. Fluoxetine | MedlinePlus

  3. Fluoxetine (Prozac) | National Alliance on Mental Illness

  4. Postpartum depression statistics | Postpartum Depression

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Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.

However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.

It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.

Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.

Curious about clinical trials?

Access the latest treatments and medications. unavailable elsewhere - entirely free of charge. We make it easy to take part.