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Zyflo Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 12/2/2015

Zyflo (zileuton) is a leukotriene synthesis inhibitor used to control long-term (chronic) asthma and help decrease the number of asthma attacks. Common side effects of Zyflo include nausea, drowsiness, constipation, dizziness, trouble sleeping, gas, joint pain, eye redness, or vomiting.

The recommended dosage of Zyflo is two 600 mg tablets twice daily, after morning and evening meals, for a total daily dose of 2400 mg, or as directed by your doctor. Zyflo may interact with pimozide, propranolol, theophylline, or warfarin. Tell your doctor all medications you take. Do not drive, use machinery, or do any activity that requires alertness while taking Zyflo. If you are pregnant, only take Zyflo if clearly needed. It is not known if Zyflo is excreted in breast milk. Consult your doctor before breastfeeding.

Our Zyflo (zileuton) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is Patient Information Overview?

A concise overview of the drug for the patient or caregiver from First DataBank.

Zyflo Overview - Patient Information: Side Effects

SIDE EFFECTS: Nausea, drowsiness, constipation, dizziness, trouble sleeping, gas, joint pain, eye redness, or vomiting may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: chest pain, neck pain/stiffness.

Tell your doctor immediately if any of these rare but very serious side effects occur: mental/mood changes (e.g., agitation, aggression, hallucinations, abnormal dreams, depression, suicidal thoughts/suicide), yellowing skin/eyes, dark urine, severe stomach/abdominal pain, unusual tiredness, flu-like symptoms (e.g., headache, fever, chills, muscle aches).

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire patient information overview for Zyflo (Zileutin)

What is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Zyflo FDA Prescribing Information: Side Effects
(Adverse Reactions)


Clinical Studies

A total of 5542 patients have been exposed to zileuton in clinical trials, 2252 of them for greater than 6 months and 742 for greater than 1 year.

Adverse events most frequently occurring (frequency ≥ 3%) in ZYFLO-treated patients and at a frequency greater than placebo-treated patients are summarized in Table 2.

TABLE 2 : Proportion of Patients Experiencing Adverse Events in Placebo-Controlled Studies in Asthma

BODY SYSTEM/Evcnt ZYFLO 600 mg 4 times daily % Occurrence
(N =475)
Placebo % Occurrence
(N = 491)
  Headache 24.6 24.0
  Fain (unspecified) 7.8 5.3
  Abdominal Pain 4.6 2.4
  Asthenia 3.8 2.4
  Accidental Injury 3.4 2.0
  Dyspepsia 8.2* 2.9
  Nausea 5.5 3.7
  Myalgia 3.2 2.9
*p ≤ 0.05 vs placebo

Less common adverse events occurring at a frequency of greater than 1% and more commonly in ZYFLO-treated patients included: arthralgia, chest pain, conjunctivitis, constipation, dizziness, fever, flatulence, hypertonia, insomnia, lymphadenopathy, malaise, neck pain/rigidity, nervousness, pruritus, somnolence, urinary tract infection, vaginitis, and vomiting.

The frequency of discontinuation from the asthma clinical studies due to any adverse event was comparable between ZYFLO (9.7%) and placebo-treated (8.4%) groups.

In placebo-controlled clinical trials, the frequency of ALT elevations ≥ 3xULN was 1.9% for ZYFLO-treated patients, compared with 0.2% for placebo-treated patients. In controlled and uncontrolled trials, one patient developed symptomatic hepatitis with jaundice, which resolved upon discontinuation of therapy. An additional 3 patients with transaminase elevations developed mild hyperbilirubinemia that was less than three times the upper limit of normal. There was no evidence of hypersensitivity or other alternative etiologies for these findings. ZYFLO is contraindicated in patients with active liver disease or transaminase elevations greater than or equal to 3xULN (see CONTRAINDICATIONS). It is recommended that hepatic transaminases be evaluated at initiation of and during therapy with ZYFLO (see PRECAUTIONS, Hepatic).

Occurrences of low white blood cell count ( ≤ 2.8 x 109/L) were observed in 1.0% of 1,678 patients taking ZYFLO and 0.6% of 1,056 patients taking placebo in placebo-controlled studies. These findings were transient and the majority of cases returned toward normal or baseline with continued ZYFLO dosing. All remaining cases returned toward normal or baseline after discontinuation of ZYFLO. Similar findings were also noted in a long-term safety surveillance study of 2458 patients treated with ZYFLO plus usual asthma care versus 489 patients treated only with usual asthma care for up to one year. The clinical significance of these observations is not known.

In the long-term safety surveillance trial of ZYFLO plus usual asthma care versus usual asthma care alone, a similar adverse event profile was seen as in other clinical trials.

Post-Marketing Experience

Cases of sleep disorders and behavior changes have been reported (see PRECAUTIONS, Neuropsychiatric Events). Rash and urticaria have also been reported with ZYFLO.

Read the entire FDA prescribing information for Zyflo (Zileutin)

Zyflo - User Reviews

Zyflo User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Zyflo sorted by most helpful. Patient Discussions FAQs

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Allergies & Asthma

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