Zyflo (Zileuton) – Oral

What Is Zyflo?

Zyflo (zileuton) is a prescription drug used in adults and children 12 years or older to treat or prevent asthma. Since this drug is not a rescue inhaler, it cannot be used to treat an active asthma attack.

Zileuton belongs to the class of drugs known as 5-lipoxygenase inhibitors. It works by blocking the formation of a specific chemical in the body called leukotriene, which causes asthma symptoms, including airway blockage.

Zyflo is available as a tablet in immediate-release and controlled-release formulations.

Drug Facts

Generic Name: Zileuton

Brand Name(s): Zyflo

Drug Availability: Prescription

Therapeutic Classification: 5-lipoxygenase inhibitors

Available Generically: Yes

Controlled Substance: N/A

Administration Route: Oral

Active Ingredient: Zileuton

Dosage Form(s): Tablet (Regular-release, Controlled-release)

What Is Zyflo Used For?

Zyflo (Zileuton) is used to treat or prevent asthma, a condition that affects about 300 million people worldwide. Asthma is also more prevalent in children, and it is the most noncommunicable (chronic) disease in children. It can be triggered by respiratory infections and environmental allergens, including smoke.

Zileuton is approved for use in adults and children 12 years and older.

How to Take Zyflo 

Take Zyflo daily as instructed by your healthcare provider. 

  • Extended-release: Take within one hour after food. Do not crush, chew, or break. Swallow the tablet whole.
  • Immediate-release: Take with or without food.

This medicine prevents you from having episodes of asthma. Hence, keep taking it even if you feel better.


Store tablet at room temperature (68 to 77 degrees Fahrenheit) away from light. Store in a dry place. Do not store it in your bathroom.

Keep all your medications away from the reach of children and pets.

Discard any unused or expired drugs. Ask your pharmacist if you do not know the best ways to discard your medicine. Ask about drug take-back programs in your area.

How Long Does Zyflo Take to Work?

Zyflo is easily well-absorbed by the body, taking about 1.7 hours to peak in your system.

What Are the Side Effects of Zyflo?

This is not a complete list of side effects and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a healthcare provider. You may report side effects to the Food and Drug Administration (FDA) at fda.gov/medwatch or 800-FDA-1088.

Many people notice no negative side effects at all from taking Zyflo. However, some people do experience problems while taking the medication.

Common Side Effects

Common side effects of Zyflo include but are not limited to:

  • Diarrhea
  • Sore throat
  • Stuffy nose
  • Headache
  • Stomach pain
  • Heartburn
  • Nausea
  • Common cold symptoms
  • Muscle pain

Severe Side Effects

Zyflo can cause many side effects. Some may be life-threatening. Call your healthcare provider promptly if you have serious side effects. If your symptoms seem life-threatening or if you think you have a medical emergency, call 911. Severe side effects include:

  • Trouble sleeping or sleep disorders
  • Behavioral changes
  • Liver issues like yellow skin, dark urine, lack of appetite, fatigue, abdominal pain, or light-colored stools
  • Signs of an allergic reaction like hives, tightness in the chest or throat, and trouble breathing

This is not a complete list of side effects. Talk to your healthcare provider if you have questions.

Zyflo can cause liver problems. Hence, people using this medicine long-term should have their liver routinely monitored by a healthcare provider.

Report Side Effects

Zyflo may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much of Zyflo Should I Take?

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The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (extended-release tablets):
    • For asthma prevention:
      • Adults and children 12 years of age and older—Two 600 milligram (mg) tablets two times a day, within one hour after morning and evening meals.
      • Children up to 12 years of age—Use and dose must be determined by your doctor.


Pregnancy: Uncontrolled asthma during pregnancy may increase the risk of severe conditions like low birth weight, gestational diabetes, or preeclampsia. However, due to limited studies on this population, zileuton is not the preferred drug to use in pregnant people.

Pregnant people exposed to Zyflo should enroll in the MotherToBaby Pregnancy Studies through the website or by calling 877-311-8972. This will help monitor any reactions or adverse outcomes in the person carrying the baby and the infant.

Breastfeeding: It is unknown if Zyflo is present in breast milk. However, due to the possible harmful effects of Zyflo in breastfeeding infants, your healthcare provider may consider the benefits of breastfeeding to the infant and the benefits of treatment to the mother, to the risk of infant exposure before prescribing this medicine.

Children: Due to the risk of liver toxicity, the manufacturer does not recommend using zileuton in children under 12 years old.

Adults over age 65: There are generally no differences between how Zyflo works in younger adults compared to people over 65. However, people assigned female at birth who are over age 65 may be at a higher risk for liver issues. Nevertheless, healthcare providers should monitor how your liver works while on this medication, regardless of age.

Missed Dose

Regular-Release Tablets

If you mistakenly forget to take your immediate-release medicine, take the missed dose as soon as you think about it. Skip your missed dose if it is too close to the next dose. Return to your regular dosing schedule. Do not take extra tablets or more than one dose at a time.

Extended-Release Tablets

Skip the missed dose and return to your normal time. Do not take extra doses or two doses at the same time.

Overdose: What Happens If I Take Too Much Zyflo?

Information about the overdose of Zyflo in humans is limited.

What Happens If I Overdose on Zyflo?

Call your medical provider or the Poison Control Center right away if you think you or someone else may have ingested or overdosed on Zyflo. 

If someone passes out or isn't breathing after taking zileuton, call 911 immediately.


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It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to check for unwanted effects.

Check with your doctor if you are using more inhalations (puffs) than usual of your inhaled bronchodilator to relieve an acute asthma attack.

You may be taking other medicines for asthma along with zileuton. Do not stop taking or reduce the dose of the other medicines, even if your asthma seems better, unless you are told to do so by your doctor.

You should limit the amount of alcohol you drink while you are taking this medicine.

This medicine may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed and have problems with sleep. If you or your caregiver notice any of these side effects, tell your doctor right away.

What Are Reasons I Shouldn't Take Zyflo? 

Avoid taking Zyflo if you have:

  • Active liver disease or abnormal liver enzymes (transaminase) three times higher than the normal levels.
  • Hypersensitivity to zileuton or any part of its formulation.

What Other Medications Interact With Zyflo?

Certain medications interact with Zyflo and increase the risk of severe side effects. Some of the drugs to avoid are:

Talk to your healthcare provider before starting or stopping any medications, including over-the-counter (OTC) ones.

What Medications Are Similar?

Other drugs similar to Zyflo used to treat and prevent asthma include:

This is a list of drugs that also prevent and treat asthma. It is not a recommended list of medicines to take with Zyflo. You should not take these drugs together unless your healthcare provider tells you to. Ask your pharmacist or a healthcare provider if you have questions.

Frequently Asked Questions

  • What is Zyflo used to treat?

    Zyflo is used to prevent and treat asthma in adults and children 12 years and older.

  • What are the common side effects of Zyflo?

    Some common side effects include:

    • Dry mouth
    • Anxiety
    • Fatigue
    • Headache
    • Diarrhea
    • Nausea
    • Loss of energy
    • Trouble sleeping
    • Blurred vision
    • Constipation
    • Application site irritation, itching, or redness
  • Where should I store Zyflo?

    Store the tablet at room temperature (68 to 77 degrees Fahrenheit), away from light, in a dry place. Do not store it in your bathroom.

How Can I Stay Healthy While Taking Zyflo?

Asthma can be very manageable when you focus on preventing and controlling its symptoms. Here are a few things you can do to stay healthy while on Zyflo:

  • Avoid exposure to triggers, stress, and irritants.
  • Avoid smoking, as it may trigger your asthma.
  • Always carry an EpiPen, especially if you are at risk of anaphylaxis.
  • Stay on top of your yearly influenza vaccine and pneumococcal vaccinations.
  • Take your medicine routinely. Do not stop taking it, even if you feel fine.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

4 Sources
Verywell Health 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. Food and Drug Administration. Zyflo label.

  2. Maciag MC, Phipatanakul W. Prevention of Asthma: Targets for Intervention. Chest. 2020;158(3):913-922. doi:10.1016/j.chest.2020.04.011

  3. Castillo JR, Peters SP, Busse WW. Asthma Exacerbations: Pathogenesis, Prevention, and Treatment. J Allergy Clin Immunol Pract. 2017;5(4):918-927. doi:10.1016/j.jaip.2017.05.001

  4. Food and Drug Administration. Zyflo CR label

By Queen Buyalos, PharmD
Queen Buyalos is a pharmacist and freelance medical writer. She takes pride in advocating for cancer prevention, overall health, and mental health education. Queen enjoys counseling and educating patients about drug therapy and translating complex ideas into simple language.