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Zyflo CR Side Effects

Generic Name: zileuton

Note: This page contains side effects data for the generic drug zileuton. It is possible that some of the dosage forms included below may not apply to the brand name Zyflo CR.

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

As well as its needed effects, zileuton (the active ingredient contained in Zyflo CR) may cause unwanted side effects that require medical attention.

Major Side Effects

If any of the following side effects occur while taking zileuton, check with your doctor immediately:

  • 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

Minor Side Effects

Some zileuton side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned 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.[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 CR (zileuton)." Cornerstone Therapeutics, Cary, NC.

2. "Product Information. Zyflo (zileuton)." Abbott Pharmaceutical, Abbott Park, IL.

3. "Product Information. Zylo Filmtab (zileuton)." Abbott Pharmaceutical, Abbott Park, IL.

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 19 (1992): 1537-41

5. 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 22 (1995): 462-8

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 119 (1993): 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 275 (1996): 931-6

It is possible that some side effects of Zyflo CR may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

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