SIDE EFFECTS: Flu-like symptoms (e.g., fever, chills, muscle aches, fatigue, headache, joint pain, nausea, stomach pain, cough) may occur. If instructed to do so, you may take pain/fever-reducing medications (e.g., acetaminophen, ibuprofen) to help with these symptoms. Dry mouth, loss of appetite, weight loss, trouble sleeping, diarrhea, dry skin, or redness/swelling at the injection site may also occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.

Temporary hair loss may occur. Normal hair growth should return after treatment has ended.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including: persistent sore throat or fever, easy or unusual bleeding/bruising, unusually severe fatigue, unusually slow/fast/pounding heartbeat, change in the amount of urine, severe stomach pain with nausea/vomiting, black/tarry stools, vomit that looks like coffee grounds, yellowing eyes or skin, dark urine, increased thirst, increased urination, bloody diarrhea, numbness/tingling of arms/legs.

Get medical help right away if any of these rare but very serious side effects occur: chest pain, vision changes, seizures, one-sided weakness.

This drug may infrequently cause severe mental/mood changes (e.g., suicidal thoughts or severe depression). If you notice these symptoms, stop your treatment with peginterferon and get medical help right away.

A very serious allergic reaction to this drug is unlikely, but get medical help right away if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the Pegasys (peginterferon alfa-2a) Side Effects Center for a complete guide to possible side effects »

PRECAUTIONS: Before using peginterferon alfa-2a, tell your doctor or pharmacist if you are allergic to it; or to polyethylene glycol (PEG); or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: other severe liver disease (e.g., autoimmune hepatitis, hepatic decompensation).

Before taking this medication, tell your doctor or pharmacist your medical history, especially of: psychiatric conditions (e.g., depression), low blood counts (e.g., red cells, white cells, or platelets), heart disease, thyroid problems, autoimmune disease (e.g., rheumatoid arthritis, lupus, psoriasis), eye problems, kidney disease, lung disease (e.g., COPD, asthma, pneumonia), history of cancer, intestinal disease ( e.g., colitis), pancreatitis, history of drug/alcohol abuse, diabetes, other infections (e.g., HIV, hepatitis B, chickenpox), high blood triglyceride levels, history of organ transplant, liver problems (other than hepatitis C).

Do not have immunizations/vaccinations without the consent of your doctor.

Use caution with sharp objects like safety razors or nail cutters and avoid activities such as contact sports to lower the chance of getting cut, bruised, or injured.

This drug may make you drowsy or dizzy. Do not drive, use machinery, or do any activity that requires alertness until you are sure you can perform such activities safely.

This medicine may cause stomach bleeding. Daily use of alcohol and this medicine may increase your risk for stomach bleeding.

Caution is advised when using this drug in the elderly because they may be more sensitive to its effects.

This medication is not recommended for use during pregnancy because of possible serious harm to the unborn baby. Consult your doctor for more details and to discuss reliable forms of birth control. It is recommended that men and women use birth control measures while being treated with this medication and for the 6 months after treatment has stopped. If you become pregnant or think you may be pregnant, inform your doctor immediately.

It is unknown if this drug passes into breast milk. Consult your doctor before breast-feeding.