Discover WELIREG

WELIREG™ (belzutifan) can help you take action for certain VHL disease-related tumors

Clinical trial results for WELIREG


WELIREG was studied in a clinical trial of adults with certain VHL disease-related tumors.

Questions to ask your doctor


Make the most of your next visit by talking to your doctor about your treatment options.

Learn about a savings offer


Learn how eligible, privately insured patients may be able to lower the out-of-pocket cost on a prescription of WELIREG.

Understanding VHL disease

VHL disease is a rare genetic condition in which cysts and tumors unpredictably grow throughout the body. Understanding VHL disease-related tumors and how they occur can help you make treatment decisions with your doctor.

Filling a WELIREG prescription

Merck is committed to helping make treatment available to those who need it. Learn about your options for getting your prescribed WELIREG medication.

Patient & caregiver resources

Find helpful information about VHL disease-related tumors and how WELIREG may help. Plus, get tips for managing treatment along the way.

What is WELIREG?

WELIREG is a prescription medicine used to treat adults with von Hippel-Lindau (VHL) disease who need treatment for a type of kidney cancer called renal cell carcinoma (RCC), tumors in the brain and spinal cord called central nervous system hemangioblastomas, or a type of pancreatic cancer called pancreatic neuroendocrine tumors, that do not need surgery right away.

It is not known if WELIREG is safe and effective for use in children.

Important Safety Information

WELIREG may cause serious side effects. WELIREG may cause harm to your unborn baby.

  • A pregnancy test will be done before you start treatment.
  • Birth control methods that contain hormones may not work as well during treatment.
  • Females and males with female partners who can become pregnant should use an effective form of non-hormonal birth control (contraception) during treatment and for 1 week after your last dose.

WELIREG may cause serious side effects, including:

Low red blood cell counts (anemia). Low red blood cell counts are common with WELIREG and can be severe. You may need a blood transfusion if your red blood cell counts drop too low. Your health care provider will do blood tests to check your red blood cell counts before you start and during treatment with WELIREG. Tell your health care provider if you get any symptoms of low red blood cell counts, including tiredness, feeling cold, shortness of breath, chest pain, or fast heartbeat.

Low oxygen levels in your body. WELIREG can cause low oxygen levels in your body that can be severe and may require you to stop treatment with WELIREG, receive oxygen therapy, or be hospitalized. Your health care provider will monitor your oxygen levels before you start and during treatment with WELIREG. Tell your health care provider or get medical help right away if you get symptoms of low oxygen in your body, including shortness of breath or increased heart rate.

Harm to your unborn baby. Treatment with WELIREG during pregnancy can cause harm to your unborn baby.

Females who are able to become pregnant:

  • Your health care provider will do a pregnancy test before you start treatment with WELIREG.
  • You should use an effective form of non-hormonal birth control (contraception) during treatment with WELIREG and for 1 week after your last dose.
  • Birth control methods that contain hormones (such as birth control pills, injections, or transdermal system patches) may not work as well during treatment with WELIREG.
  • Talk to your health care provider about birth control methods that may be right for you during treatment with WELIREG.
  • Tell your health care provider right away if you become pregnant or think you may be pregnant during treatment with WELIREG.

Males with female partners who are able to become pregnant:

  • You should use effective birth control (contraception) during treatment with WELIREG and for 1 week after your last dose.
  • Tell your health care provider right away if your partner becomes pregnant or thinks she is pregnant while you are taking WELIREG.

Before taking WELIREG, tell your health care provider about all of your medical conditions, including if you:

  • have low red blood cell counts (anemia)
  • are pregnant or plan to become pregnant
  • are breastfeeding or plan to breastfeed. It is not known if WELIREG passes into your breast milk. Do not breastfeed during treatment with WELIREG and for 1 week after your last dose.

Tell your health care provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. WELIREG and certain other medicines can affect each other and cause serious side effects.

The most common side effects of WELIREG include:

  • feeling tired
  • increased creatinine (kidney function test)
  • headache
  • feeling dizzy
  • increased blood sugar (glucose) levels
  • nausea

WELIREG may cause fertility problems in males and females, which may affect your ability to have children. Talk to your health care provider if this is a concern for you.

These are not all the possible side effects of WELIREG. Call your health care provider for medical advice about side effects.

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch or call 1-800-FDA-1088.

Please read the Medication Guide for WELIREG, including additional important information on the above warning about harm to an unborn baby, and discuss it with your doctor. The physician Prescribing Information also is available.