Avonex Side Effects Center

Last updated on RxList: 11/16/2021
Avonex Side Effects Center

What Is Avonex?

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.

What Are Side Effects of Avonex ?

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 of Avonex. Some patients using interferon medications such as Avonex have become depressed or had suicidal thoughts. Tell your doctor immediately if this occurs. Tell your doctor right away if you have any serious side effects of Avonex 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 or vomiting,
  • stomach or abdominal pain, or
  • dark urine.

Dosage for Avonex

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.

What Drugs, Substances, or Supplements Interact with Avonex ?

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 (nonsteroidal anti-inflammatory drugs), or seizure medications drug interactions. Tell your doctor all medications you are taking.

Avonex During Pregnancy and Breastfeeding

Avonex is not recommended for use during pregnancy. It is unknown if this drug passes into breast milk. Consult your doctor before breastfeeding.

Additional Information

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 kind of disease is multiple sclerosis? See Answer
Avonex Consumer Information

Get emergency medical help if you have signs of an allergic reaction (hives, itching, anxiety, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Interferon beta-1a can cause life-threatening blood clots in the small blood vessels inside your organs, such as your brain or kidneys. Seek medical help right away if you have symptoms of this condition, such as a fever, tiredness, decreased urination, bruising, or nosebleeds.

Call your doctor at once if you have:

  • pain, swelling, bruising, redness, oozing, or skin changes where the injection was given;
  • a light-headed feeling, like you might pass out;
  • unusual changes in mood or behavior (feeling hopeless, anxious, nervous, irritable, or depressed);
  • thoughts about suicide or hurting yourself;
  • easy bruising, unusual bleeding;
  • a seizure;
  • heart problems--swelling, rapid weight gain, feeling short of breath, rapid heartbeats, chest pain spreading to your jaw or shoulder, nausea, sweating;
  • liver problems--nausea, loss of appetite, tiredness, confusion, easy bruising or bleeding, dark urine, clay-colored stools, or jaundice (yellowing of your skin or eyes);
  • signs of infection--fever, chills, cough with mucus, bloody diarrhea, pain or burning when you urinate; or
  • thyroid problems--mood swings, trouble sleeping, tiredness, hunger, diarrhea, pounding heartbeats, muscle weakness, sweating, dry skin, thinning hair, menstrual changes, weight changes, puffiness in your face, feeling more sensitive to hot or cold temperatures.

Common side effects may include:

  • low blood cell counts;
  • skin changes where the injection was given;
  • depression;
  • abnormal liver function tests;
  • stomach pain; or
  • flu symptoms--headache, fever, chills, chest pain, back pain, tiredness, weakness, muscle aches.

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 Multiple Sclerosis? MS Symptoms, Causes, Diagnosis See Slideshow
Avonex Professional Information


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

  • Depression, Suicide, and Psychotic Disorders [see WARNINGS AND PRECAUTIONS]
  • Hepatic Injury [see WARNINGS AND PRECAUTIONS]
  • Anaphylaxis and Other Allergic-Reactions [see WARNINGS AND PRECAUTIONS]
  • Injection Site Reactions Including Necrosis [see WARNINGS AND PRECAUTIONS]
  • Congestive Heart Failure [see WARNINGS AND PRECAUTIONS]
  • Decreased Peripheral Blood Counts [see WARNINGS AND PRECAUTIONS]
  • Thrombotic Microangiopathy [see WARNINGS AND PRECAUTIONS]
  • Autoimmune Disorders [see WARNINGS AND PRECAUTIONS]
  • Laboratory Tests [see WARNINGS AND PRECAUTIONS]

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 14% 18%
  Dizziness 12% 14%
Respiratory System
  Upper respiratory tract infection 12% 14%
  Sinusitis 12% 14%
  Bronchitis 5% 8%
Digestive System
  Nausea 19% 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.


No Information Provided

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

© Avonex Patient Information is supplied by Cerner Multum, Inc. and Avonex Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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