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AVONEX: An established relapsing MS
treatment option for over 2 decades*

Why AVONEX

AVONEX is a once-a-week injectable treatment for relapsing multiple sclerosis (MS). It has been prescribed to over 600,000 people worldwide since its approval in 1996. Today it is the #1 prescribed interferon for relapsing MS.†

*Initial US Approval: 1996.

†This information is an estimate derived from the use of information under license from the following IQVIA information service: IQVIA NPA® NBRx monthly data for the period August 2023 - November 2025. Approximately 687,769 patients have been exposed worldwide, including 353,323 U.S. patients.

Explore more about AVONEX for relapsing MS

AVONEX efficacy

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Safety and side effects

Get details about the serious and most common side effects

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Specific populations

See additional information on use during pregnancy and lactation

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Questions for your
healthcare provider

Download a guide to help start a conversation with your healthcare provider about your relapsing MS treatment

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AVONEX Start Form

If you’re considering AVONEX, get a head start on the process by taking this form to your next visit. It includes step-by-step instructions for you and your healthcare provider

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Watch an AVONEX
patient video

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Next: AVONEX Effectiveness

What is AVONEX® (interferon beta-1a)?

AVONEX is a prescription medicine used to treat relapsing forms of multiple sclerosis (MS), to include clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease in adults.

It is not known if AVONEX is safe and effective in children.

Important Safety Information

Who should not use AVONEX?

  • Do not take AVONEX if you are allergic to interferon beta or any of the ingredients in AVONEX

Before beginning treatment, you should discuss with your healthcare provider the potential benefits and risks associated with AVONEX.

What is the most important information I should know about AVONEX?

AVONEX can cause serious side effects. Tell your healthcare provider right away if you have any of the symptoms listed below while taking AVONEX.

  • Depression, suicidal thoughts, hallucinations or other behavioral health problems. Some people taking AVONEX may develop mood or behavior problems, including irritability (getting upset easily), depression (feeling hopeless or feeling bad about yourself), nervousness, anxiety, aggressive behavior, thoughts of hurting yourself or suicide, and hearing or seeing things that others do not hear or see (hallucinations)

If you have any of these mood or behavior problems, your healthcare provider may tell you to stop taking AVONEX.

  • Liver problems, or worsening of liver problems including liver failure and death. Tell your healthcare provider right away if you have any of these symptoms: Nausea, loss of appetite, tiredness, dark colored urine and pale stools, yellowing of your skin or the white part of your eye, bleeding more easily than normal, confusion, and sleepiness. During your treatment with AVONEX you will need to see your healthcare provider regularly and have regular blood tests to check for side effects. Tell your healthcare provider about all the medicines you take and if you drink alcohol before you start taking AVONEX
  • Serious allergic reactions and skin reactions. Serious allergic and skin reactions can happen when you take AVONEX. Symptoms of serious allergic and skin reactions may include itching, swelling of the face, eyes, lips, tongue or throat, trouble breathing, anxiousness, feeling faint, and skin rash, hives, sores in your mouth, or your skin blisters and peels

Get emergency help right away if you have any of these symptoms. Talk to your healthcare provider before taking another dose of AVONEX.

Before taking AVONEX, tell your healthcare provider about all of your medical conditions, including if you:

  • are being treated for a mental illness, or had treatment in the past for any mental illness, including depression and suicidal behavior
  • have or had bleeding problems or blood clots, have or had low blood cell counts, have or had liver problems, have or had seizures (epilepsy), have or had heart problems, have or had thyroid problems, have or had any kind of autoimmune disease (where the body’s immune system attacks the body’s own cells)
  • drink alcohol
  • have or have had an allergic reaction to rubber or latex. The tip cap of the AVONEX prefilled syringe and prefilled autoinjector Pen contain natural rubber latex
  • are pregnant or plan to become pregnant. It is not known if AVONEX can harm your unborn baby
  • are breastfeeding or plan to breastfeed. AVONEX may pass into your breastmilk. Talk with your healthcare provider about the best way to feed your baby if you take AVONEX

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements.

What are the possible side effects of AVONEX?

AVONEX can cause serious side effects, including:

  • Injection site reactions. AVONEX may cause redness, pain, itching, or swelling at the place where your injection was given. Call your healthcare provider right away if an injection site becomes swollen and painful or the area looks infected. You may have a skin infection or an area of severe skin damage (necrosis) requiring treatment by a healthcare provider
  • Heart problems, including heart failure. Some people who did not have a history of heart problems developed heart muscle problems or congestive heart failure after taking AVONEX. If you already have heart failure, AVONEX may cause your heart failure to get worse. Call your healthcare provider right away if you have worsening symptoms of heart failure such as shortness of breath or swelling of your lower legs or feet while using AVONEX
    • Some people using AVONEX may have other heart problems including low blood pressure, fast or abnormal heartbeat, chest pain, and heart attack or a heart muscle problem (cardiomyopathy)
  • Blood problems. AVONEX can affect your bone marrow and cause low red and white blood cell, and platelet counts. In some people, these blood cell counts may fall to dangerously low levels. If your blood cell counts become very low, you can get infections and problems with bleeding and bruising
  • Thrombotic microangiopathy (TMA). TMA is a condition that involves injury to the smallest blood vessels in your body. TMA can also cause injury to your red blood cells (the cells that carry oxygen to your organs and tissues) and your platelets (cells that help your blood clot) and can sometimes lead to death. Your healthcare provider may tell you to stop taking AVONEX if you develop TMA
  • Pulmonary arterial hypertension. Pulmonary arterial hypertension can occur with interferon beta products, including AVONEX. Symptoms may include new or increasing fatigue or shortness of breath. Contact your healthcare provider right away if you develop these symptoms
  • Seizures. Some people have had seizures while taking AVONEX, including people who have never had seizures before. Tell your healthcare provider right away if you have a seizure
  • Autoimmune diseases. Problems with easy bleeding or bruising (idiopathic thrombocytopenia), thyroid gland problems (hyperthyroidism and hypothyroidism), and autoimmune hepatitis have happened in some people who use AVONEX

The most common side effects of AVONEX include:

  • Flu-like symptoms. Most people who take AVONEX have flu-like symptoms especially early during the course of therapy. Usually, these symptoms last for a day after the injection. Symptoms may include muscle aches, fever, tiredness, and chills

You may be able to manage these flu-like symptoms by taking over-the-counter pain and fever reducers. Talk with your healthcare provider about ways to help if you develop flu-like symptoms while taking AVONEX.

These are not all of the possible side effects of AVONEX.

Call your healthcare provider for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Please see full Prescribing Information and Medication Guide.

This information does not take the place of talking with your healthcare provider about your medical condition or your treatment.
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©2026 Biogen. All rights reserved. AVX-US-0589v9 07/26
For US healthcare professionals only.
All trademarks are the property of their respective owners.