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Welireg Side Effects

Generic name: belzutifan

Medically reviewed by Last updated on Jan 2, 2023.

Note: This document contains side effect information about belzutifan. Some dosage forms listed on this page may not apply to the brand name Welireg.

Applies to belzutifan: oral tablet.


Oral route (Tablet)

Warning: Embryo-fetal toxicityExposure to belzutifan during pregnancy can cause embryo-fetal harm.Verify pregnancy status prior to the initiation of belzutifan.Advise patients of these risks and the need for effective non-hormonal contraception. Belzutifan can render some hormonal contraceptives ineffective.

Serious side effects of Welireg

Along with its needed effects, belzutifan (the active ingredient contained in Welireg) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking belzutifan:

More common

  • Blurred vision
  • change in vision
  • chest tightness
  • confusion
  • cough
  • difficulty swallowing
  • dizziness
  • fast heartbeat
  • headache
  • hives, itching, skin rash
  • nervousness
  • pale skin
  • pounding in the ears
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • seeing flashes or sparks of light
  • seeing floating spots before the eyes, or a veil or curtain appearing across part of vision
  • trouble breathing
  • unusual bleeding or bruising
  • unusual tiredness or weakness

Other side effects of Welireg

Some side effects of belzutifan may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Body aches or pain
  • chills
  • constipation
  • difficulty in moving
  • ear congestion
  • fever
  • loss of voice
  • muscle aches, cramps, pain, or stiffness
  • nausea
  • pain in the joints
  • sneezing
  • sore throat
  • stomach pain
  • stuffy or runny nose
  • swollen joints
  • weight increased

For Healthcare Professionals

Applies to belzutifan: oral tablet.


Very common (10% or more): Hemoglobin decreased (93%), anemia (90%), leukocytes decreased (11%)[Ref]


Very common (10% or more): Arthralgia (18%), myalgia (16%)[Ref]


Very common (10% or more): Visual impairment (e.g., vision blurred, central retinal vein occlusion and retinal detachment) (21%)[Ref]


Very common (10% or more): weight increased (12%)[Ref]


Very common (10% or more): Upper respiratory tract infection (e.g., bronchitis, sinusitis, upper respiratory tract infection, viral upper respiratory infection) (21%), dyspnea (20%)

Common (1% to 10%): Hypoxia[Ref]


Very common (10% or more): Creatinine increased (64%), fatigue/asthenia (64%), glucose increased (34%), alanine aminotransferase (ALT) increased (20%), aspartate aminotransferase (AST) increased (16%), calcium decreased (10%), leukocytes decreased (11%)[Ref]

Nervous system

Very common (10% or more): Headache/migraine (39%), dizziness/vertigo (38%)[Ref]


Very common (10% or more): Hypertension (13%)[Ref]


Very common (10% or more): Nausea (31%), constipation (13%), abdominal pain (e.g., abdominal discomfort, abdominal pain, abdominal pain upper, abdominal pain lower) (13%)[Ref]


1. "Product Information. Welireg (belzutifan)." Merck & Company Inc (2021):

Further information

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

Some side effects may not be reported. You may report them to the FDA.