The most common side effects with Pegasys (seen in more than 1 patient in 10) are anorexia (loss of appetite), headache, insomnia (difficulty sleeping), irritability, depression, dizziness, nausea (feeling sick), diarrhoea, abdominal (tummy) pain, alopecia (hair loss), pruritus (itching), myalgia (muscle pain), arthralgia (joint pain), fatigue (tiredness), pyrexia (fever), rigors (shaking chills), reactions at the site of the injection and pain.