What are effects of pegasys (peginterferon alfa 2a)?

Depends: From a hepatitis c treatment standpoint, using Pegasys (peginterferon alfa 2a) in combination with Ribavirin and a protease inhibitor can have dramatic treatment effect (i.e. Lead to cure of hepatitis c depending on the stage of your liver disease). Now "side-effects" can range from "flu-like" symptoms to lab abnormalities, depression, rash, GI symptoms, anxiety/irritability, insomnia, etc. Discuss with your doctor.