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.