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Zyflo (zileuton)

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Zyflo® (zileuton) is an oral drug used as part of a preventive and long-term treatment plan for asthma. It is not a rescue inhaler and will not help an asthma attack that has already started. Your doctor may also prescribe short-acting bronchodilators for emergency relief of an acute asthma attack.1,2

How does Zyflo work?

Zyflo works by blocking the formation of chemicals called leukotrienes. These chemicals cause airway inflammation that leads to asthma symptoms like wheezing, coughing, and shortness of breath.1,2

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What are the ingredients in Zyflo?

The active ingredient in Zyflo is zileuton.1

What are the possible side effects of Zyflo?

The most common side effects of Zyflo include:1,2

  • Stomach (abdominal) pain
  • Upset stomach
  • Nausea
  • Headache
  • Diarrhea
  • Muscle pain
  • Nose and throat irritation

Zyflo may increase liver enzymes in some people. Liver enzymes can be measured by a blood test. Your doctor will check your liver enzyme levels before and during treatment with Zyflo. People who have liver disease or high levels of liver enzymes should not take Zyflo. Tell your doctor if you have symptoms of increased liver enzymes while taking Zyflo, such as:1

  • Tiredness
  • Flu-like symptoms
  • Itching
  • Yellow skin
  • Yellow color in the whites of your eyes
  • Urine that is darker than normal

These are not all the possible side effects of Zyflo. Talk to your doctor about what to expect when taking Zyflo. You also should call your doctor if you have any changes that concern you when taking Zyflo.

Other things to know

Before taking Zyflo, tell your doctor if you:1

  • Have ever had liver disease, hepatitis, jaundice (yellow eyes or skin), or dark urine
  • Drink alcohol
  • Are taking theophylline for your asthma, the blood thinner drug warfarin, or the blood pressure drug propranolol

Zyflo may harm an unborn baby and pass into breast milk. Before starting treatment with Zyflo, tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding. Together you can decide whether Zyflo is right for you.1

Before beginning treatment for asthma tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you are taking. This includes over-the-counter drugs.

For more information, read the full prescribing information of Zyflo.