Common side effects of alpha interferon and peginterferon (occurring in more than 10 percent of patients) include

• fatigue
• muscle aches
• headaches
• nausea and vomiting
• skin irritation at the injection site
• low-grade fever
• weight loss
• irritability
• depression
• mild bone marrow suppression
• hair loss (reversible)

Most of these side effects are mild to moderate in severity and can be managed. They are worse during the first few weeks of treatment, especially with the first injection. Thereafter, side effects diminish. Acetaminophen may be helpful for the muscle aches and low-grade fever. Fatigue and depression are occasionally so troublesome that the dose of interferon should be decreased or therapy stopped early. Depression and personality changes can occur on interferon therapy and be quite subtle and not readily admitted by the patient. These side effects need careful monitoring. Patients with depression may benefit from antidepressant therapy using selective serotonin reuptake inhibitors. Generally, the psychiatric side effects resolve within 2 to 4 weeks of stopping combination therapy.

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health