Avonex is a prescription medicine used to treat multiple sclerosis. It is a form of a protein called beta interferon that occurs naturally in the body. The way Avonex works in MS is not fully understood. It is thought to work by limiting the destruction of the protective coating around the nerve fibers by stopping the immune system from attacking the nerve fibers.

Avonex comes as a powder to be mixed into a solution for injection, and also as a prefilled injection syringe. This medication is injected into a muscle, usually once a week, on the same day each week. It is best to inject the medication at around the same time of day on your injection days, usually in the late afternoon or evening. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand.

Some common side effects of Avonex include headaches, flu-like symptoms, muscle pain and fever.