Do you mean Pegasys? This drug is used for the treatment of Hepatitis C (although it is not a cure). The chemical compound is called Peginterferon Alfa-2a.
'SIDE EFFECTS that may occur while using this medicine include headache; dizziness; drowsiness; tiredness; weakness; dry mouth; taste changes; loss of appetite; nausea; vomiting; diarrhea; trouble sleeping; temporary hair loss; dry or irritated skin; increased sweating; and redness, swelling, or pain at the injection site. If they continue or are bothersome, check with your doctor. CHECK WITH YOUR DOCTOR AS SOON AS POSSIBLE if you experience muscle or joint pain; burning, numbness, or tingling or your arms, hands, legs, or feet; stomach pain; confusion; irritability, anxiety, or nervousness; or weight loss. CONTACT YOUR DOCTOR IMMEDIATELY if you experience mood or mental changes (such as depression, aggressive or unusual behavior, hallucinations, or thoughts of hurting yourself); flu-like symptoms (such as fever, chills, or persistent sore throat); difficulty hearing or loss of hearing; easy bruising or bleeding; yellowing of your eyes or skin; dark urine; unusual or severe fatigue; severe or persistent stomach pain, nausea, vomiting, or diarrhea; unusually pale stools or black, tarry stools; unusually increased thirst; lower back pain; an unusual increase or decrease in the amount of your urine; an unusually fast, slow, or irregular heartbeat; sharp or crushing chest pain; sudden shortness of breath; sudden leg pain; sudden severe headache, vomiting, dizziness, or fainting; changes in vision; numbness of an arm or leg; or one-sided weakness. An allergic reaction to this medicine is unlikely, but seek immediate medical attention if it occurs. Symptoms of an allergic reaction include rash, itching, swelling, severe dizziness, or trouble breathing. If you notice other effects not listed above, contact your doctor, nurse, or pharmacist.'