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Avonex Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 10/5/2015

Avonex (Interferon beta-1a) is a 166 amino acid glycoprotein used to treat relapsing multiple sclerosis (MS). Avonex will not cure MS, it will only decrease the frequency of relapse symptoms. Common side effects of Avonex include injection site reactions (pain, swelling, or redness), dizziness, stomach pain, or runny or stuffy nose. Flu-like symptoms such as headache, fatigue, fever, chills, and muscle aches may occur when you first start Avonex. These symptoms usually last about a day after the shot and improve or go away after a few months of continued use. Some patients using interferon medications such as Avonex have become depressed or had suicidal thoughts. Tell your doctor immediately if this occurs.

The recommended dosage of Avonex is 30 mcg injected intramuscularly once a week. This medication is intended for use under the guidance and supervision of a physician. Patients may self-inject only if their physician determines it is appropriate and after proper training in intramuscular injection technique. Avonex may interact with acetaminophen, cancer medications, tuberculosis medications, birth control pills or hormone replacement therapy, methotrexate, arthritis medications, antibiotics, HIV/AIDS medications, cholesterol medications, ACE inhibitors, NSAIDs (non-steroidal anti-inflammatory drugs), or seizure medications drug interactions. Tell your doctor all medications you are taking. Avonex is not recommended for use during pregnancy. It is unknown if this drug passes into breast milk. Consult your doctor before breast-feeding.

Our Avonex (Interferon beta-1a) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is Patient Information in Detail?

Easy-to-read and understand detailed drug information and pill images for the patient or caregiver from Cerner Multum.

Avonex in Detail - Patient Information: Side Effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

  • depressed mood, anxiety, trouble sleeping, restlessness, or thoughts of suicide or hurting yourself;
  • easy bruising or bleeding, weakness;
  • seizure (convulsions);
  • numbness or tingling in your hands or feet;
  • pain or burning when you urinate;
  • pain, swelling, or skin changes where the injection was given;
  • fever, chills, body aches, flu symptoms; or
  • nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Less serious side effects may include:

  • headache, dizziness;
  • stomach pain; or
  • runny or stuffy nose.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Avonex (Interferon beta-1a)

What is Patient Information Overview?

A concise overview of the drug for the patient or caregiver from First DataBank.

Avonex Overview - Patient Information: Side Effects

SIDE EFFECTS: Pain, swelling, or redness at the injection site may occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.

Flu-like symptoms such as headache, fatigue, fever, chills, and muscle aches may occur when you first start this medication. These symptoms usually last about a day after the shot and improve or go away after a few months of continued use. You can minimize these side effects by injecting this medicine at bedtime and using fever reducers/pain relievers such as acetaminophen or ibuprofen before each dose. Consult your doctor or pharmacist for more information.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including: mental/mood changes (e.g., depression, thoughts of suicide, new or worsening psychiatric symptoms), hair loss, vision changes, persistent fatigue, numbness/tingling/swelling of the hands/ankles/feet, muscle weakness, trouble breathing, sudden weight gain, gradual change in weight (without a change in diet or exercise), cold or heat intolerance, slow/fast/irregular heartbeat, easy bleeding or bruising, signs of infection (e.g., fever, persistent sore throat), yellowing eyes or skin, persistent nausea/vomiting, stomach/abdominal pain, dark urine.

Get medical help right away if any of these rare but very serious side effects occur: chest pain, seizures.

A very serious allergic reaction to this drug is unlikely, but get medical help right away if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

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

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire patient information overview for Avonex (Interferon beta-1a)

What is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Avonex FDA Prescribing Information: Side Effects
(Adverse Reactions)


The following serious adverse reactions are discussed in more detail in other sections of labeling:

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of AVONEX cannot be directly compared to rates in clinical trials of other drugs and may not reflect the rates observed in practice.

Among 351 patients with relapsing forms of MS treated with AVONEX 30 micrograms (including 319 patients treated for 6 months and 288 patients treated for greater than one year) the most commonly reported adverse reactions (at least 5% more frequent on AVONEX than on placebo) were flu-like symptoms. Symptoms can include chills, fever, myalgia and asthenia occurring within hours to days following an injection. Most people who take AVONEX have flu-like symptoms 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. The most frequently reported adverse reactions resulting in clinical intervention (for example, discontinuation of AVONEX or the need for concomitant medication to treat an adverse reaction symptom) were flu-like symptoms and depression.

Table 2 enumerates adverse reactions that occurred with AVONEX-treated patients at an incidence of at least 2% more than that observed in the placebo-treated patients in the pooled placebo-controlled studies in patients with relapsing forms of MS [see Clinical Studies].

Table 2: Adverse Reactions in the Placebo-Controlled Studies

Adverse Reaction Placebo
(N = 333)
(N = 351)
Body as a Whole
  Headache 55% 58%
  Flu-like symptoms (otherwise unspecified) 29% 49%
  Pain 21% 23%
  Asthenia 18% 24%
  Fever 9% 20%
  Chills 5% 19%
  Abdominal pain 6% 8%
  Injection site pain 6% 8%
  Infection 4% 7%
  Injection site inflammation 2% 6%
  Chest pain 2% 5%
  Injection site reaction 1% 3%
  Toothache 1% 3%
Nervous System
  Depression 1 4% 1 8%
  Dizziness 1 2% 1 4%
Respiratory System
  Upper respiratory tract infection 12% 14%
  Sinusitis 1 2% 1 4%
  Bronchitis 5% 8%
Digestive System
 Nausea 1 9% 23%
Musculoskeletal System
  Myalgia 22% 29%
  Arthralgia 6% 9%
  Urinary tract infection 15% 17%
 Urine constituents abnormal 0% 3%
Skin and Appendages
  Alopecia 2% 4%
Special Senses
  Eye disorder 2% 4%
Hemic and Lymphatic System
  Injection site ecchymosis 4% 6%
  Anemia 1% 4%
Cardiovascular System
  Migraine 3% 5%
  Vasodilation 0% 2%


Anaphylaxis and other allergic reactions have occurred in AVONEX-treated patients [see WARNINGS AND PRECAUTIONS]. As with all therapeutic proteins, there is a potential for immunogenicity. In studies assessing immunogenicity in multiple sclerosis patients administered AVONEX for at least 1 year, 5% (21 of 390 patients) showed the presence of neutralizing antibodies at one or more times.

These data reflect the percentage of patients whose test results were considered positive for antibodies to AVONEX using a two-tiered assay (ELISA binding assay followed by an antiviral cytopathic effect assay), and are highly dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of neutralizing activity in an assay may be influenced by several factors including sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies to AVONEX with the incidence of antibodies to other products may be misleading.

Postmarketing Experience

The following additional adverse reactions have been identified during post-approval use of AVONEX. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Read the entire FDA prescribing information for Avonex (Interferon beta-1a)

Avonex - User Reviews

Avonex User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Avonex sorted by most helpful. Patient Discussions FAQs

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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