Inteferon
Most persons have flu-like symptoms (fever, chills, headache, muscle and joint aches, fast heart rate) early in treatment, but these lessen with continued treatment. Later side effects may include tiredness, hair loss, low blood count, trouble with thinking, moodiness, and depression. Severe side effects are rare (seen in less than 2 out of 100 persons). These include thyroid disease, depression with suicidal thoughts, seizures, acute heart or kidney failure, eye and lung problems, hearing loss, and blood infection. Although rare, deaths have occurred due to liver failure or blood infection, mostly in persons with cirrhosis. An important side effect of interferon is worsening of liver disease with treatment, which can be severe and even fatal. Interferon dosage must be reduced in up to 40 out of 100 persons because of severity of side effects, and treatment must be stopped in up to 15 out of 100 persons. Pregnant women should not be treated with interferon

Interferon and Ribivarin Combination
In addition to the side effects due to interferon described above, ribavirin can cause serious anemia (low red blood cell count) and can be a serious problem for persons with conditions that cause anemia, such as kidney failure. In these persons, combination therapy should be avoided or attempts should be made to correct the anemia. Anemia caused by ribavirin can be life-threatening for persons with certain types of heart or blood vessel disease. Ribavirin causes birth defects and pregnancy should be avoided during treatment. Patients and their healthcare providers should carefully review the product manufacturer information prior to treatment.