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Welireg

Pronunciation: Well-ih-reg
Generic name: belzutifan
Dosage form: tablet (40mg)
Drug class: Miscellaneous antineoplastics

Medically reviewed by Melisa Puckey, BPharm. Last updated on May 28, 2025.

What is Welireg?

Welireg (belzutifan) is a prescription medication used to treat adults with von Hippel-Lindau (VHL) disease, pheochromocytoma or paraganglioma (PPGL), and renal cell carcinoma (RCC)  in certain patients. Welireg is a hypoxia-inducible factor (HIF) inhibitor that works by blocking HIF-2a, to help reduce tumor growth.

Welireg is a hypoxia-inducible factor (HIF) inhibitor. Welireg is not chemotherapy.

Welireg mechanism of action is blocking HIF-2a, a protein that promotes tumor growth under low-oxygen conditions, which are common in certain cancers. By inhibiting this protein, Welireg can slow or stop the growth of tumors.

Welireg tablets are taken once a day, with or without food. Tablets should be swallowed whole, and do not crush, chew, or break them.

In von Hippel-Lindau (VHL) disease in Welireg helps to reduce the size of tumors, including tumors in the brain and spinal cord called central nervous system hemangioblastomas, pancreatic neuroendocrine tumors, and renal cell carcinomas, in patients who do not require immediate surgery. 

Welireg is manufactured for Merck Sharp & Dohme Corp.

What is Welireg used for?

Welireg is FDA approved to treat:

Welireg side effects

Common Welireg side effects when taken for VHL disease may include lower hemoglobin, headache, dizziness, tiredness, nausea, increased blood sugar (increased thirst or urination, dry mouth, fruity breath), or abnormal kidney function tests.

Common Welireg side effects when taken for advanced RCC may include decreased hemoglobin, tiredness, muscle and joint pain, changes in laboratory readings, increased creatinine, decreased lymphocytes, increased alanine aminotransferase, decreased sodium, increased potassium, and increased aspartate aminotransferase. 

Serious Welireg side effects 

Get emergency medical help if you have signs of an allergic reaction: hives, difficulty breathing, swelling of your face, lips, tongue, or throat.

Call your doctor right away if you have:

Welireg may also cause the serious side effects of pneumonia, hemorrhage, pleural effusion, sepsis, and hemorrhage. 

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Welireg may cause other serious side effects, including in the Warnings section.

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 the FDA at 1-800-FDA-1088.

Warnings

Welireg can cause anemia (low red blood cells) or low oxygen levels. These conditions may need to be treated with blood transfusions, oxygen therapy, or hospitalization. You will have blood tests to check your red blood cell counts before you start and during treatment. Tell your healthcare provider if you get any symptoms of low red blood cell counts, including tiredness, feeling cold, shortness of breath, chest pain, or fast heartbeat.

Welireg may harm an unborn baby. Both men and women should use effective non-hormonal birth control to prevent pregnancy while using Welireg and for at least 1 week after the last dose. See ‘Before taking this medication’ section for more information on pregnancy and breastfeeding.

Before taking this medicine

Before taking Welireg, tell your healthcare provider about all of your medical conditions, including if you:

Pregnancy

Tell your healthcare provider if you are pregnant or plan to become pregnant, as Welireg may harm an unborn baby if the mother or father is using this medicine. Both men and women should use effective non-hormonal birth control to prevent pregnancy while using Welireg and for at least 1 week after the last dose.

Females who are able to become pregnant 

Males with female partners who are able to become pregnant:

Fertility

Welireg may cause fertility problems in males and females, which may affect your ability to have children. The reversibility of the effect on fertility is unknown. Talk to your healthcare provider if this is a concern for you. 

Using Welireg with hormonal contraceptives may stop the hormonal contraceptive from working (contraceptive failure).

Breastfeeding 

Do not breastfeed while using this medicine, and for at least 1 week after your last dose.

How should I take Welireg?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Welireg directions

Welireg can cause anemia (low red blood cells) or low oxygen levels. These conditions may need to be treated with blood transfusions, oxygen therapy, or hospitalization.

You will need frequent medical tests, even if you have no symptoms.

Do not change your dose or stop using a medicine without your doctor's advice.

Welireg dosing information

Usual Adult Welireg Dose: 120 mg orally once daily until disease progression or unacceptable toxicity.  The dose may be changed due to side effects.

Usual Pediatric Welireg Dose: is based on body weight

Welireg is available as 40mg tablets.

What happens if I miss a dose?

If you miss a dose, take it as soon as possible on the same day. Then take your next dose at your regular time the next day. Do not take extra tablets to make up for the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What other drugs will affect Welireg?

Many drugs can interact with Welireg, and some drugs should not be used at the same time. Tell your doctor about all other medicines you use. This includes prescription and over-the-counter medicines, vitamins, and herbal products.

Using Welireg with hormonal contraceptives may stop the hormonal contraceptive from working or there may be an increase in breakthrough bleeding.

Not all possible interactions are listed here.

Does Welireg interact with my other drugs?

Enter medications to view a detailed interaction report using our Drug Interaction Checker.

Welireg Package Insert 

HCPs and patients often use the Welireg Package Insert for more detailed information about this medicine. The Welireg Package Insert contains more comprehensive information on Indications and Usage, Dosage and Administration, Clinical Pharmacology, Clinical Studies, Drug Interaction, and more. Discuss any medical questions you have with your doctor or other health care provider. This is not all the information you need to know about this medicine for safe and effective use, and it does not take the place of talking to your doctor about your treatment.

The Package Insert is sometimes called Welireg Prescribing Information (PI) or  FDA label.

Storage

Ingredients

Active ingredient: belzutifan
Inactive ingredients: croscarmellose sodium, hypromellose acetate succinate, magnesium stearate, mannitol, microcrystalline cellulose, and silicon dioxide. 

The film-coating contains FD&C Blue #2 aluminum lake, polyethylene glycol, polyvinyl alcohol, talc, and titanium dioxide.

Company

Manufactured for Merck Sharp & Dohme.

Further information

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