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 require surgery right away.

It is not known if this medicine is safe and effective in children.

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 healthcare provider will do 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.
• 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, receive oxygen therapy, or be hospitalized. Your healthcare provider will monitor your oxygen levels before you start, and during treatment. Tell your healthcare 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 healthcare 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, 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 healthcare provider about birth control methods that may be right for you during treatment with Welireg.
  • Tell your healthcare provider right away if you become pregnant or think you may be pregnant during treatment.

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 healthcare provider right away if your partner becomes pregnant or thinks she is pregnant while you are taking Welireg.

See Welireg side effects for more information about side effects.

• Take Welireg exactly as your healthcare provider tells you.
• Do not stop taking Welireg or change your dose without talking to your healthcare provider.
• Take your prescribed dose of Welireg one time a day, at the same time each day.
• Your healthcare provider may change your dose, temporarily stop, or permanently stop treatment if you have certain side effects.
• Take Welireg tablets with or without food.
• Swallow the tablets whole. Do not chew, crush, or split the tablets.
• 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.
• If you vomit after taking a dose, do not take an extra dose. Take your next dose at your regular time the next day.
• If you take too much or overdose, call your healthcare provider or go to the nearest emergency room right away.

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

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

Tell your healthcare 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.

Know the medicines you take. Keep a list of them to show to your healthcare provider and pharmacist when you get a new medicine.

Welireg may cause serious side effects, including:

• See Important information

The most common side effects 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 healthcare provider if this is a concern for you.

These are not all the possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Many drugs can interact with belzutifan, 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. Not all possible interactions are listed here.