Pegasys 135mcg Injection is used in the treatment of chronic hepatitis C virus (HCV) infection and chronic hepatitis B virus (HBV) infection. Pegasys 135mcg Injection is given as an injection by a qualified medical professional. You should continue to take it as long as your doctor advises it. The duration of treatment varies according to your need and response to treatment. You should take it exactly as your doctor has advised. Taking it in the wrong way or taking too much can cause very serious side effects. It may take several weeks or months for you to see or feel the benefits but do not stop taking it unless your doctor tells you to. Some common side effects of this medicine include headache, sweating, joint pain, and flu-like symptoms. This medicine may reduce the number of blood cells in your blood, thereby, increasing the susceptibility to infections. Hence, inform your doctor if you notice fever, chills, rash, trouble breathing, unusual bleeding or bruising, and dark-colored urine. Regular blood tests are required to check your blood cells along with thyroid, liver, kidney, and serum electrolytes levels. Before taking it, tell your doctor if have liver, or kidney problems or have mental illness. You must inform your doctor about mental illness, mood changes, depression, vision change, and suicidal thoughts as this medicine can worsen the situation. Many other medicines can affect, or be affected by, this medicine so let your healthcare team know all medications you are using. This medicine is not recommended during pregnancy or while breastfeeding. The use of effective contraception by both males and females during treatment is important to avoid pregnancy.