AVONEX safety and side effects

Experience and safety in the treatment of relapsing MS

Understanding AVONEX safety and potential side effects

Are you and your healthcare provider considering AVONEX? If so, there are a few important topics to discuss. To help prepare for your discussion, you can learn more below.

The safety of AVONEX was studied in 2 well-controlled clinical trials conducted over 2 to 3 years.

Understanding serious side effects

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.

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, or hearing or seeing things that others do not hear or see (hallucinations).

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
  • 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. Symptoms of serious allergic and skin reactions may include:

  • itching
  • swelling of the face, eyes, lips, tongue, or throat
  • trouble breathing
  • anxiousness
  • feeling faint
  • 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.

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.

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.

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.


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.

Understanding the most common side effects of AVONEX

It’s important to talk with your healthcare provider about the most common AVONEX side effects and how to help manage them. 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. For many people, these symptoms lessen or go away over time. Symptoms may include:

  • muscle aches
  • fever
  • tiredness
  • chills

Experiencing flu-like symptoms doesn’t mean you actually have the flu. These symptoms may be part of your body’s natural response to interferon beta-1a.

These are not all of the possible side effects of AVONEX. Call your healthcare provider for medical advice about side effects.


More to check out

Questions for your
healthcare provider

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

Download guide
Biogen Support Services

If you’re living with relapsing MS, know that you’re not alone. Biogen Support Services is here to help

Get support today

Explore more about AVONEX for relapsing MS

Starting AVONEX

Learn about AVONEX dosing and what you should know before starting treatment

Get started
AVONEX effectiveness

Review the results from AVONEX clinical trials

See results