Belzutifan (Welireg™)

Author: Christina Bach, MBE, LCSW, OSW-C
Content Contributor: Christopher Tweed, PharmD, BCOP
Last Reviewed: August 11, 2023

Pronounce: bel-zoo-ti-fan

Classification: Hypoxia-inducible factor-2 alpha (HIF-2α) inhibitor

About: Belzutifan (Welireg™)

Belzutifan (Welireg™) is a hypoxia-inducible factor-2 alpha (HIF-2α) inhibitor used for the treatment of von Hippel-Lindau (VHL) disease. In VHL, the body overproduces HIF-2α, leading to an increased risk of cancer cell development/growth. Belzutifan (Welireg™) works to block these mechanisms that make cells reproduce rapidly, and influence tumor growth.

How to Take Belzutifan

This medication comes in tablet form to be taken by mouth. It can be taken with or without food. It should be swallowed whole, it should not be broken, crushed, or chewed. It is usually taken once a day. If you miss a dose, take it as soon as possible that day, then take your next dose at the usual time on the next day. Don’t take extra doses to make up for a missed dose. If you vomit after taking this medication, don’t take an extra dose.

It is important to make sure you are taking the correct amount of medication every time. Before every dose, check that what you are taking matches what you have been prescribed.

Belzutifan can be affected by certain medications. Be sure to tell your healthcare provider about all medications and supplements you take. It can also impact how well hormonal birth control (birth control pills, some IUD’s, injections, vaginal rings, and skin patches), works so you should use a non-hormonal method (condom, diaphragm, sponge, copper IUD, cervical cap) of birth control during treatment and for 1 week after the last dose.

Storage and Handling

Store your medication in the original, labeled container at room temperature and in a dry location (unless otherwise directed by your healthcare provider or pharmacist). This medication should not be stored in a pillbox. Keep containers out of reach of children and pets.

If a caregiver prepares your dose for you, they should consider wearing gloves or pour the pills directly from their container into the cap, a small cup, or directly into your hand. They should avoid touching the pills. They should always wash their hands before and after giving you the medication. Pregnant or nursing women should not prepare the dose for you. Ask your oncology team where to return any unused medication for disposal. Do not flush down the toilet or throw it in the trash.

Where do I get this medication?

Certain cancer medications are only available through specialty pharmacies. If you need to get this medication through a specialty pharmacy, your provider will help you start this process. Where you can fill your prescriptions may also be influenced by your prescription drug coverage. Ask your health care provider or pharmacist for assistance in identifying where you can get this medication.

Insurance Information

This medication may be covered under your prescription drug plan. Patient assistance may be available to qualifying individuals depending upon prescription drug coverage. Co-pay cards, which reduce the patient co-pay responsibility for eligible commercially (non-government sponsored) insured patients, may also be available. Your care team can help you find these resources if they are available.

Possible Side Effects of Belzutifan

There are a number of things you can do to manage the side effects of belzutifan. Talk to your care team about these recommendations. They can help you decide what will work best for you. These are some of the most common or important side effects:


Your red blood cells are responsible for carrying oxygen to the tissues in your body. When the red cell count is low, you may feel tired or weak. You should let your oncology care team know if you experience any shortness of breath, difficulty breathing, or pain in your chest. If the count gets too low, you may receive a blood transfusion.


Fatigue is very common during cancer treatment and is an overwhelming feeling of exhaustion that is not usually relieved by rest. While on cancer treatment, and for a period after, you may need to adjust your schedule to manage fatigue. Plan times to rest during the day and conserve energy for more important activities. Exercise can help combat fatigue; a simple daily walk with a friend can help. Talk to your healthcare team for helpful tips on dealing with this side effect.


Your healthcare provider can recommend medications and other strategies to help relieve pain.

Nausea and/or Vomiting

Talk to your oncology care team so they can prescribe medications to help you manage nausea and vomiting. In addition, dietary changes may help. Avoid things that may worsen the symptoms, such as heavy or greasy /fatty, spicy or acidic foods (lemons, tomatoes, oranges). Try saltines or ginger ale to lessen symptoms.

Call your oncology care team if you are unable to keep fluids down for more than 12 hours or if you feel lightheaded or dizzy at any time.

Visual Changes

This medication can cause blurred vision, retinal detachment, and central retinal vein occlusion. Contact your care team if you have changes in your vision.

Less common, but important side effects can include:

  • Hypoxia: When the level of oxygen in your blood (also called oxygen saturation or pulse ox) is too low, it is called hypoxia. Belzutifan can cause hypoxia. Your blood oxygen will be measured with a pulse ox reader on your finger before and during treatment. Let your team know right away if you are having a hard time breathing or catching your breath, or feel dizzy or lightheaded.
  • Kidney problems: This medication can cause kidney problems, including an increased creatinine level, which your oncology care team may monitor for using blood tests. Notify your healthcare provider if you notice decreased urine output, blood in the urine, swelling in the ankles, or loss of appetite
  • High blood sugar: This medication can cause elevated blood sugar levels in patients with and without diabetes. Your oncology care team will monitor your blood sugar. If you develop increased thirst, urination or hunger, blurry vision, headaches or your breath smells like fruit, notify your healthcare team. Diabetics should monitor their blood sugar closely and report elevations to the healthcare team.

Reproductive Concerns

Exposure of an unborn child to this medication could cause birth defects, so you should not become pregnant or father a child while on this medication. Effective non-hormonal birth control (condoms, diaphragm, copper IUD, cervical cap, and sponge) is necessary during treatment and for at least 1 week after treatment. Even if your menstrual cycle stops or you believe you are not producing sperm, you could still be fertile and conceive. You should not breastfeed while taking this medication or for 1 week after your last dose.