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Generic Name: zileuton (zye LOO ton)
Brand Name: Zyflo, Zyflo CR
Physician reviewed Zyflo patient information - includes Zyflo description, dosage and directions.
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Drug Information:
Zyflo is a leukotriene (loo-koe-TRY-een) inhibitor. Leukotrienes are chemicals your body releases when you breathe in an allergen (such as pollen). These chemicals cause swelling in your lungs and tightening of the muscles around your airways, which can result in asthma symptoms. Zyflo is used to prevent asthma attacks in adults and children as young as 12 years old. Zyflo may also be used for purposes not listed in this medication guide. Call your doctor at once if you have nausea, upper stomach pain, itching, loss of appetite, dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes). These may be early signs of liver problems. Learn more

Zyflo Side Effects

Zyflo Side Effects

Note: This document contains side effect information about zileuton. Some of the dosage forms listed on this page may not apply to the brand name Zyflo.

In Summary

More frequent side effects include: dyspepsia. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to zileuton: oral tablet, oral tablet extended release

Along with its needed effects, zileuton (the active ingredient contained in Zyflo) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking zileuton:


  • Flu-like symptoms
  • itching
  • right upper stomach pain
  • unusual tiredness or weakness
  • yellow eyes or skin

Incidence not known

  • Attack, assault, or force
  • attempts at killing oneself
  • discouragement
  • dry mouth
  • fear or nervousness
  • feeling sad or empty
  • hyperventilation
  • irregular heartbeats
  • irritability
  • lack of appetite
  • loss of interest or pleasure
  • restlessness
  • seeing, hearing, or feeling things that are not there
  • shakiness in the legs, arms, hands, or feet
  • shortness of breath
  • sleeplessness
  • tiredness
  • trembling or shaking of the hands or feet
  • trouble with concentrating
  • trouble with sleeping
  • unable to sleep

Some side effects of zileuton may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Cough
  • fever
  • headache
  • nausea
  • pain or tenderness around the eyes and cheekbones
  • stuffy or runny nose
  • tightness of the chest or wheezing
  • troubled breathing
  • upset stomach

Less common

  • Abdominal or stomach pain
  • sore throat
  • weakness

For Healthcare Professionals

Applies to zileuton: oral tablet, oral tablet extended release


The most commonly occurring adverse reactions are sinusitis, nausea, and pharyngolaryngeal pain.

Nervous system

Very common (10% or more): Headache (up to 24.6%)

Common (1% to 10%): Hypertonia, nervousness, dizziness, somnolence


Common (1% to 10%): Pruritus, urticaria


Common (1% to 10%): Dyspepsia (8.2%), nausea (5.5%), diarrhea (5%), abdominal pain, upper abdominal pain, vomiting, constipation, flatulence


Common (1% to 10%): Urinary tract infection, vaginitis


Common (1% to 10%): Low white blood cell count (2.6%)

The WBC counts returned to normal or baseline following discontinuation of this drug. The clinical significance of these findings is not known.


Common (1% to 10%): Hepatotoxicity, ALT elevations (1.8%)

Postmarketing reports: Hepatic injury, including death, life-threatening liver injury with recovery, symptomatic jaundice, hyperbilirubinemia, and elevations of ALT more than 8 times ULN

The majority of ALT elevations (82%) were reported within the first 3 months of treatment and resolved within 21 days for most of these patients after discontinuation of the drug. In the extended release group, the majority of ALT elevations (60%) occurred in the first month of treatment; in a few patients, the levels returned to less than 2 times ULN or normal within 9 and 12 days.

The hepatic function enzyme elevations did not result in any cases of jaundice, development of chronic liver disease, or death in this clinical trial. In patients who discontinued this drug, ALT levels dropped below 2 times ULN in approximately one month.


Common (1% to 10%): Hypersensitivity, rash


Common (1% to 10%): Lymphadenopathy


Common (1% to 10%): Myalgia (7%), arthralgia, neck pain/rigidity


Common (1% to 10%): Conjunctivitis


Common (1% to 10%): Pain (7.8%), asthenia (3.8%), accidental injury (3.4%), fever, malaise


Common (1% to 10%): Insomnia

Postmarketing reports: Sleep disorders, behavior changes


Common (1% to 10%): Upper respiratory tract infections (9%), sinusitis (6.5%), pharyngolaryngeal pain (5%), chest pain

Editorial References and Review

Medically reviewed by BestRx Medical Team Last updated on 1/1/2020.

Source: Drugs.com Zyflo