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Zyflo Side Effects

Generic name: zileuton

Medically reviewed by Last updated on Jul 13, 2023.

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

Applies to zileuton: oral tablet, oral tablet extended release.

Serious side effects of Zyflo

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:


Incidence not known

Other side effects of Zyflo

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

Less common

For Healthcare Professionals

Applies to zileuton: oral tablet, oral tablet extended release.


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

Nervous system

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

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


Common (1% to 10%): Pruritus, urticaria[Ref]


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


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


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

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


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[Ref]

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.[Ref]


Common (1% to 10%): Hypersensitivity, rash[Ref]


Common (1% to 10%): Lymphadenopathy[Ref]


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


Common (1% to 10%): Conjunctivitis[Ref]


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


Common (1% to 10%): Insomnia

Postmarketing reports: Sleep disorders, behavior changes[Ref]


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


1. Product Information. Zyflo (zileuton). Abbott Pharmaceutical. 2016.

2. Product Information. Zyflo CR (zileuton). Cornerstone Therapeutics. 2016.

3. Hackshaw KV, Shi Y, Brandwein SR, Jones K, Westcott JY. A pilot study of zileuton, a novel selective 5-lipoxygenase inhibitor, in patients with systemic lupus erythematosus. J Rheumatol. 1995;22:462-8.

4. Weinblatt ME, Kremer JM, Coblyn JS, Helfgott S, Maier AL, Petrillo G, Henson B, Rubin P, Sperling R. Zileuton, a 5-lipoxygenase inhibitor in rheumatoid arthritis. J Rheumatol. 1992;19:1537-41.

5. Product Information. Zyflo (zileuton). Abbott Pharmaceutical. PROD.

6. Israel E, Rubin P, Kemp JP, Grossman J, Pierson W, Siegel SC, Tinkelman D, Murray JJ, Busse W, Segal AT, et al. The effect of inhibition of 5-lipoxygenase by zileuton in mild-to- moderate asthma. Ann Intern Med. 1993;119:1059-66.

7. Israel E, Cohn J, Dube L, Drazen JM. Effect of treatment with zileuton, a 5-lipoxygenase inhibitor, in patients with asthma. A randomized controlled trial. Zileuton Clinical Trial Group. JAMA. 1996;275:931-6.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.