Brand Name(s)
- United States: Welireg
- Canada: Welireg
Warning(s)
Belzutifan is a cancer medicine. It can cause serious side effects. Read these safety points and talk with your care team about any questions.
- Pregnancy risk: This drug may harm an unborn baby. You will have a pregnancy test before starting. Use effective nonhormonal birth control (like condoms, copper IUD) while taking it and for 1 week after the last dose.
- Hormonal birth control (pills, patch, ring, shot, implant) may not work as well. Use a nonhormonal method as backup.
- If your sex partner could become pregnant, use birth control while on treatment and for 1 week after the last dose.
- Do not breastfeed while taking this drug and for 1 week after the last dose.
- Drug interactions: Some medicines and supplements can change how belzutifan works. Always tell your doctors and pharmacist about everything you take. Do not start, stop, or change any medicine without checking first.
- Low red blood cells (anemia) can happen and may be severe. Your team will check your blood counts. Call if you feel very tired, dizzy, short of breath, pale, or have a fast heartbeat.
- Low oxygen levels (hypoxia) can happen and may be severe. Your oxygen will be monitored. Call if you have shortness of breath, chest pain, blue lips, confusion, or new/worse dizziness.
- Blood pressure changes (high or low) can occur. Report severe headache, vision changes, fainting, or pounding heart.
- Blood sugar changes can occur. If you have diabetes, monitor as directed and report big changes.
- Electrolyte changes can occur. Report confusion, severe weakness, cramps, shaking, seizures, or uneven heartbeat.
- Allergic reactions can happen. Get urgent help for rash, hives, swelling of the face or throat, wheezing, or trouble breathing.
- Older adults (65+) may have more side effects. Extra monitoring may be needed.
- Fertility: This drug may affect the ability to become pregnant or to father a child. It is not known if this improves after treatment.
- Tell all of your health care providers and dentists that you take belzutifan.
Call your care team right away or seek emergency care for: shortness of breath; chest pain or pressure; fast or irregular heartbeat; severe or persistent headache; passing out; swelling; unusual bleeding or bruising; vision changes; numbness or tingling; feeling very cold; or signs of a severe allergic reaction.
Kind of Cancers It Is Used For (not a complete list)
- Tumors linked to von Hippel–Lindau (VHL) disease that need treatment.
- Kidney cancer (renal cell carcinoma) in adults.
- Pheochromocytoma (adrenal gland tumor) and paraganglioma.
Your oncology team will decide if belzutifan is appropriate for your cancer type and situation.
Mechanism of Action
Belzutifan is a targeted therapy called a hypoxia-inducible factor 2 alpha (HIF-2α) inhibitor. Many tumors turn on HIF-2α to survive low-oxygen conditions and to grow new blood vessels.
By blocking HIF-2α, belzutifan slows signals that help cancer cells grow and form blood vessels. It can also lower the hormone erythropoietin (EPO), which may lead to low red blood cells (anemia) and low oxygen levels.
Common Side Effects
Not everyone has side effects, and many are manageable. Tell your care team if symptoms are severe or do not improve.
- Feeling tired or weak
- Dizziness or headache
- Cold-like symptoms; stuffy or runny nose
- Muscle or joint pain
- Stomach pain
- Changes in appetite; weight gain
- Nausea or vomiting
- Constipation or diarrhea
Serious effects can also happen, including anemia, low oxygen levels, blood pressure or blood sugar changes, electrolyte problems, unusual bleeding or bruising, chest pain, heart rhythm changes, swelling, vision changes, severe allergic reactions, or numbness/tingling. Get medical help right away for urgent symptoms.
Last reviewed: 2025-12-15
