Skip to main content
Rx pad with bottle representing Prozac side effects
Drug Info

Prozac side effects and how to avoid them

Prozac increases serotonin in the brain, allowing people to better manage mood and impulses
Cropped SingleCare logo
By | Aug. 31, 2021 Medically reviewed by Josephine Bawab, Pharm.D.

Prozac side effects | Serious side effects | Insomnia | Diarrhea | Erectile dysfunction | Angle-closure glaucoma | Suicide | How long do side effects last? | Warnings | Interactions | How to avoid side effects

Prozac is a brand-name prescription drug used for the treatment of major depressive disorder (MDD), obsessive-compulsive disorder (OCD), panic disorder, binge eating disorder, and bulimia nervosa. Prozac is also combined with the antipsychotic medication olanzapine for treatment-resistant depression or depressive episodes in people diagnosed with bipolar disorder. 

Prozac is also commonly used off-label to treat premenstrual dysphoric disorder, generalized anxiety disorder, social anxiety disorder, post-traumatic stress disorder, borderline personality disorder, and other conditions.

The active ingredient in Prozac, fluoxetine hydrochloride, is a selective serotonin reuptake inhibitor (SSRI). SSRIs increase serotonin in the brain, allowing people to better manage mood and impulses due to more efficient nerve activity. As with all medicines that affect the brain, Prozac can cause problems due to side effects, pre-existing conditions, or drug interactions, but there are ways to avoid or minimize these problems.

RELATED: Learn more about Prozac

Common side effects of Prozac

The most common side effects of Prozac are:

  • Trouble sleeping
  • Nausea
  • Headache
  • Fatigue
  • Diarrhea
  • Loss of appetite
  • Drowsiness
  • Dry mouth
  • Weight loss
  • Weight gain

Serious side effects of Prozac

The most serious side effects of fluoxetine include:

  • Drug-induced movement problems (extrapyramidal effects)
  • Suicidal thoughts and behaviors
  • Irregular heartbeats (QT prolongation) and heart problems
  • Seizures
  • Bleeding
  • Serotonin syndrome
  • Mania or hypomania
  • Low sodium
  • Low blood sugar
  • Angle-closure glaucoma
  • Pulmonary fibrosis
  • Prolonged and painful erections
  • Severe allergic reactions

Prozac and insomnia

In clinical trials, 10% to 33% of people taking Prozac experienced trouble sleeping. If Prozac causes insomnia, patients will initially be advised to take the daily dose early in the morning. If insomnia persists, a healthcare professional will typically prescribe mirtazapine, trazodone, or a sedative along with Prozac. Both mirtazapine and trazodone are antidepressants like Prozac, but they also have powerful sedative effects.

Prozac and diarrhea

Diarrhea was experienced by 8% to 18% of people taking Prozac during its initial clinical trials. Gastrointestinal side effects, however, may get better as the body adjusts to Prozac. If diarrhea persists, a healthcare provider may prescribe mirtazapine along with Prozac. Diarrhea could, however, be a potentially serious problem in any person with an electrolyte imbalance.

Prozac and erectile dysfunction

About 1% to 7% of patients report erectile dysfunction (ED) when taking Prozac. Another 2% to 8% report ejaculation dysfunction. A healthcare provider may prescribe Wellbutrin (bupropion) or an ED medication such as Viagra (sildenafil) or Cialis (tadalafil) for erectile dysfunction. Saffron may help with ejaculation dysfunction. However, erectile dysfunction is a common side effect of SSRIs, so a healthcare provider may need to switch to another type of antidepressant.

Prozac and angle-closure glaucoma

Angle-closure glaucoma is caused by the closing of the opening (angle) between the iris and the cornea that drains fluid from the inside of the eye. Prozac causes pupils to dilate, so it may close that opening in people with uncorrected “narrow angles.” Pressure builds up behind the eye very rapidly and can result in permanent vision loss in less than a day. The incidence is unknown, but immediately stop taking Prozac and get emergency medical attention at any sign of angle-closure glaucoma such as:

  • Eye pain
  • Changes in vision
  • Swelling or redness in or around the eye

Prozac and suicide

Prozac and other SSRIs have a black box warning stating that taking the drug can cause children, teens, and young adults to become suicidal. The overall incidence is between 0.1% and 1%, but older adults are at a considerably lower risk. It is important that young people taking Prozac are monitored for signs of suicidality and other behaviors such as:

  • New or sudden changes in mood or behavior
  • Suicide attempts
  • Acting on dangerous impulses
  • Acting aggressively or violently
  • Thoughts about suicide or dying
  • Trouble sleeping
  • New or worsening depression or anxiety
  • Panic attacks
  • Agitation, restlessness, irritability, or anger
  • Unusual behaviors
  • Extreme increase in activity or talking

How long do side effects last?

Many common side effects will improve as the body gets used to the medicine. Fluoxetine has a half-life of two to four days, but it is converted by the body into another drug that works just like fluoxetine. That drug, norfluoxetine, has a half-life of four to 16 days. That means that the most common side effects can take anywhere from a week to a month to fade after the last dose has been taken.

Other side effects such as allergic reactions, angle-closure glaucoma, heart problems, severely low sodium, or serotonin syndrome will require medical attention to get better. Some of the most severe, such as heart problems or angle-closure glaucoma, may have life-long complications. 

Prozac contraindications & warnings

Prozac may cause problems in some people because of pre-existing physical or medical conditions.

Abuse and dependence

The U.S. Food and Drug Administration (FDA) has not classified Prozac as a controlled substance and no studies have been completed about its potential for abuse or physical dependence. Prozac was first introduced in 1987. Since then, there has been no evidence that Prozac causes withdrawal symptoms or addiction, even in patients who have been treated for fluoxetine abuse.

Overdose

An overdose of Prozac can cause serious and lifelong medical problems including death. Get emergency medical treatment if an overdose is expected or if any symptoms of an overdose are experienced. The most common symptoms of fluoxetine overdose are:

  • Seizures
  • Sleepiness
  • Fast heartbeat
  • Nausea
  • Vomiting

Restrictions

The only people who can never take Prozac are those with allergies to fluoxetine or any of the inactive ingredients in Prozac capsules.

Pre-existing conditions put people at an increased risk of adverse effects or other problems if they take Prozac. Healthcare providers will be cautious using Prozac in these people. Extra monitoring or tests may be needed to identify problems before they become worse. Other restrictions include:

  • People younger than the age of 25 years should be carefully watched for signs of worsening depression, unusual behaviors, mood changes, or suicidal thoughts or behaviors. 
  • Prozac may require regular monitoring and testing in people with heart problems including a history of irregular heartbeats, a family history of heart rhythm abnormalities, congestive heart failure, recent heart attacks, or electrolyte abnormalities. 
  • People who are “poor CYP2D6 metabolizers”—are at a higher risk for heart problems. They may require careful monitoring and dose adjustments.
  • Seniors and people with blood volume depletion require careful dosing and regular monitoring. 
  • For bipolar patients, Prozac is usually prescribed with the antipsychotic olanzapine to prevent manic or hypomanic episodes.
  • People with a history of seizures will require monitoring. 
  • People with uncorrected narrow angles are at a higher risk of narrow-angle glaucoma when taking Prozac.
  • People with diabetes will need regular blood glucose monitoring. 
  • People with bleeding problems or taking blood-thinning drugs may need to have regular INR tests, particularly when first taking Prozac.

Pregnancy and nursing

There is no evidence that fluoxetine increases the risk of birth defects or miscarriages. However, women may be advised not to take Prozac in the third trimester. There is a risk that the baby will be born with complications such as trouble breathing, withdrawal symptoms, or serotonin syndrome.

Women can take Prozac while breastfeeding, but they need to monitor the baby for possible side effects. Both fluoxetine and its active metabolite are present in breast milk. Babies exposed to the drug may experience agitation, fussiness, feeding problems, or insufficient weight gain.

Children

The U.S. Food and Drug Administration (FDA) has approved Prozac as safe and effective for children as young as 8 years of age for treatment of depression and as young as 7 years of age for obsessive-compulsive disorder. Antidepressants, however, are associated with a higher risk of worsening depression and suicidality when given to children, so caregivers should monitor the child for any behavior changes, mood changes, aggression, or thoughts about suicide or death.

Seniors

People older than 65 can take Prozac in the same doses as younger adults, but they may need to be monitored or tested regularly for low sodium or other possible side effects.

Prozac interactions

Prozac has some drug interactions with both over-the-counter and prescription drugs. Most are minor, but a few are serious enough that patients taking Prozac should be aware of them.

  • Prozac is never given along with monoamine oxidase inhibitors (MAOIs) such as Marplan (isocarboxazid), phenelzine, tranylcypromine, and selegiline.
  • Prozac is never combined with the antipsychotics pimozide and thioridazine. For the same reason, it is not combined with Cerdelga (eliglustat), a drug used to treat a rare hereditary disorder. Other drugs that affect heart rhythm, such as antiarrhythmics, will need to be used cautiously with regular ECG tests.
  • Because of the risk for serotonin syndrome, drugs that raise serotonin levels—called serotonergic drugs—should be avoided or used carefully. These include: 
  • Fluoxetine is broken down by the CYP2D6 liver enzyme. Drugs that block this enzyme will cause fluoxetine to increase to hazardous levels in the body, raising the risk of side effects and heart abnormalities.
  • Prozac must be used carefully with blood thinners such as warfarin. NSAIDs (nonsteroidal anti-inflammatory drugs) such as aspirin, ibuprofen, or naproxen also thin the blood, so bleeding episodes—particularly gastrointestinal bleeding—are more likely if they’re taken along with Prozac.

How to avoid Prozac side effects

A few guidelines can help minimize Prozac side effects:

1. Take Prozac as directed

Make sure to read the entire medication guide before taking this medicine. Take the dose as prescribed, usually 20–80 mg once daily. If a dose is missed, take it as soon as it’s remembered. If it’s nearly time to take the next dose, skip the missed dose and take the next dose as scheduled. 

2. Tell the doctor about all medical conditions

The best way to prevent adverse effects is to tell the prescribing healthcare professional about all past and present medical conditions, especially:

  • Liver problems
  • Kidney problems
  • Heart problems
  • History of seizures
  • Mania or bipolar disorder
  • Stroke
  • High blood pressure
  • Bleeding problems
  • Diabetes
  • Narrow-angle glaucoma
  • Electroconvulsive therapy (ECT)
  • Pregnancy or pregnancy plans
  • Breastfeeding or breastfeeding plans

3. Tell the doctor about all medications being taken

Drug interactions can also cause side effects, so the healthcare professional prescribing Prozac should know about all prescription and over-the-counter medications and supplements being taken, particularly:

  • MAO inhibitors
  • Medicines that treat mood, anxiety, psychosis, bipolar disorder, or other mental illnesses 
  • Amphetamines
  • Migraine medications called triptans
  • Opioids (especially tramadol or fentanyl)
  • Blood thinners such as warfarin
  • Any medication containing fluoxetine such as Symbyax or Sarafem
  • Supplements or herbal remedies like St. John’s wort or tryptophan.

4. Take Prozac in the morning

To minimize insomnia, take Prozac as early as possible in the morning.

5. Do not drink alcohol

Do not drink when taking Prozac. Combining alcohol with Prozac will only worsen sleepiness and mental impairment caused by the drug. 

6. Be careful about driving and other risky activities

Prozac can cause sleepiness and affect decision-making and response time. Avoid driving or risky activities until the effects of Prozac are well understood.

7. Eat a healthy diet

To avoid weight loss, eat a healthy diet. If weight loss becomes a problem, consult with a dietitian or nutritionist.

8. Avoid NSAIDs

Nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen can raise the risk of gastrointestinal bleeding, stomach pain, and bleeding episodes when taking Prozac. Consider using alternatives like acetaminophen instead.

9. Do not stop taking Prozac

The sudden discontinuation of Prozac may cause unpleasant side effects, so consult with a healthcare provider for medical advice if the drug is not working or the side effects are hard to bear. 

Related resources for Prozac side effects: