Interferon beta-1a is an injection used in the treatment of multiple sclerosis (MS). Sold under the brand name Avonex, this prescription medication is designed to control MS symptoms in patients with acute symptoms that come and go. Acute symptoms are most common in relapsing-remitting MS (RRMS).

The medicine contains amino acids that help mimic interferon naturally occurring in the body. It’s also derived from a group of drugs called immunomodulators, which suppress adverse immune system responses. In MS, this can help control common symptoms, such as:

  • numbness
  • muscle weakness
  • speech impairment
  • incontinence (bladder leaks)
  • vision problems

The exact function of interferon beta-1a injections is unknown. Like other medications, interferon beta-1a can’t cure MS. This injection doesn’t benefit patients with chronic progressive MS.

Proper Dosage

Unlike other injections, interferon beta-1a is a progressive drug. This means that you start off with a small dose and gradually work up to the maximum amount after one month of use. The National Multiple Sclerosis Society recommends the following dosage pattern: 

  • week 1: ¼ dose, or 7.5 micrograms
  • week 2: ½ dose, or 15 micrograms
  • week 3: ¾ dose, or 22.5 micrograms
  • week 4 and beyond: full dose, or 30 micrograms

You may be eager to feel better, and be tempted to take the full dose right away. There are extreme disadvantages to doing so, which is why the manufacturer recommends a gradual dosage. This allows your body to get used to the medication, and reduces your risk for side effects.

Timing of Doses

Taking any medicine requires a large amount of responsibility. Timing the doses is important in making sure interferon beta-1a works correctly. This is a once-a-week medication. Injecting it at the right time can reduce the risk of side effects and overdose.

You should take the medication at about the same time on the same day every week. Afternoons or evenings work best because you’re more likely to be at home in case side effects should arise.

If you forget your injection, take it as soon as you can. You shouldn’t double up on the medicine to make up for a missed dose.

Common Side Effects

Interferon beta-1a carries the risk of causing flu-like side effects as mild as nausea, or as severe as vomiting. Chills and night sweats may also occur. These side effects typically ease within the first three weeks of using the injections. Discuss long-term, flu-like symptoms with your doctor.

Other common side effects are:

  • muscle tightness and pain
  • joint pain
  • toothaches
  • runny nose
  • hair loss

Injecting interferon beta-1a can also cause bruising or irritation of the skin. Call your doctor if you experience large red bumps around the injection site. This may indicate an allergic reaction.

Serious Complications

This MS medication can also cause more serious side effects. Report the following to your doctor immediately:

  • anxiety and irritability
  • sudden weight loss
  • depression
  • confusion
  • insomnia
  • hallucinations and confusion
  • excessive fatigue
  • chest pain and/or irregular heartbeat
  • breathing difficulties
  • changes in skin color
  • body swelling

You should not take interferon beta-1a if you have a history of liver disease. One of the first signs of an adverse liver response is jaundice. This causes yellowing of the skin and eyes. Jaundice can also cause dark urine or pale bowel movements. While liver disease increases your risk, anyone can develop these side effects. If you’re using interferon beta-1a, consider regular blood tests to detect any liver problems caused by taking this medicine.

Long-Term Effects

Like other prescription medications, these injections carry the possibility of long-term side effects. Your risk is higher if you have a history of:

  • heart disease
  • depression or psychiatric disorders
  • seizures

Interferon beta-1a can also cause blood problems. Decreased red blood cell production (anemia) may reduce oxygen flow to vital organs, which can lead to fatigue. Blood cells responsible for warding off infections also can be affected. As a result, you may develop frequent infections. Follow your doctor’s advice and take regular blood tests to ensure you don’t experience these abnormal changes.


The purpose of interferon beta-1a is to help prevent MS symptoms from causing disability. The potential benefits can significantly improve your quality of life, but no MS medication is entirely without risk. You can help reduce complications by reporting all herbs and medications you take (including over-the-counter drugs) to your doctor. Consider another treatment method if you have a preexisting medical condition, such as liver or cardiovascular disease.