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. Taking WELIREG with certain other medicines can affect each
other and cause serious side effects.

The most common side effects of WELIREG in adults with VHL disease
include:

• tiredness
• increased creatinine (kidney function test)
• headache
• dizziness
• 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 of the possible side effects of WELIREG. Call your health
care provider for medical advice about side effects.

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

Copyright © 2025 Merck & Co., Inc., Rahway, NJ, USA and its affiliates.
All rights reserved.