If you have multiple sclerosis (MS), your doctor may recommend that you use Avonex.

Avonex is a prescription drug that’s used in adults to treat:

For details on these conditions and how Avonex treats them, see the “Is Avonex used for MS?” section below.

Avonex basics

Avonex is a liquid solution that you inject into a muscle once weekly.

Avonex contains the drug interferon beta-1a, which is a biologic medication. A biologic is made from parts of living organisms.

Avonex isn’t available in a biosimilar form. (Biosimilars are like generic drugs. But unlike generics, which are made for non-biologic drugs, biosimilars are made for biologic drugs.) Instead, interferon beta-1a comes only as the brand-name drug Avonex.

Read on to learn more about Avonex’s uses.

Like most drugs, Avonex may cause mild or serious side effects. The lists below describe some of the more common side effects that Avonex may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • your age
  • other health conditions you have
  • other medications you may be taking

Your doctor or pharmacist can tell you more about the potential side effects of Avonex. They can also suggest ways to help reduce side effects.

Mild side effects

Here’s a short list of some of the mild side effects that Avonex can cause. To learn about other mild side effects, talk with your doctor or pharmacist, or read Avonex’s medication guide.

Mild side effects of Avonex that have been reported include:

Mild side effects of many drugs may go away within a few days or a couple of weeks. But if they become bothersome, talk with your doctor or pharmacist.

* For more information on this side effect, see the “Side effect focus” section below.

Serious side effects

Serious side effects from Avonex can occur, but they aren’t common. If you have serious side effects from Avonex, call your doctor right away. But if you think you’re having a medical emergency, you should call 911 or your local emergency number.

Serious side effects of Avonex that have been reported include:

* For more information on this side effect, see the “Side effect focus” section below.

Allergic reaction

Some people may have an allergic reaction to Avonex.

Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include swelling under your skin, typically in your eyelids, lips, hands, or feet. They can also include swelling of your tongue, mouth, or throat, which can cause trouble breathing.

Call your doctor right away if you have an allergic reaction to Avonex. But if you think you’re having a medical emergency, call 911 or your local emergency number.

Keep in mind that the caps of Avonex prefilled syringes are made from latex. If you have an allergy to latex, the autoinjector form of the drug may be a better choice for you. Talk with your doctor to learn more.

Side effect focus

Learn more about some of the side effects Avonex may cause.

Hair loss

Hair loss is a rare side effect that you may experience from taking Avonex. Although uncommon, hair loss was reported in studies of people using Avonex.

What might help

If you notice that you’re losing your hair when taking Avonex, talk with your doctor or pharmacist. They may be able to recommend medications that you can take or use to reduce your hair loss. If the hair loss is very bothersome to you, your doctor may recommend a medication other than Avonex.

Liver damage

Although rare, liver damage is a possible side effect of using Avonex. Some people who used Avonex in studies had liver function test results that may indicate liver disease. In some cases, severe liver disease has been reported in people after they’ve used Avonex.

Even though liver damage is rare with Avonex use, you should know what the symptoms are. This helps you look out for them. Symptoms may include:

What might help

Before you start using Avonex, be sure to tell your doctor about any other medications that you take. If you’re also taking other medications that may affect your liver, Avonex may increase your risk for liver damage. Your doctor should be able to help determine your risk for liver damage.

Throughout your treatment with Avonex, your doctor will monitor your liver through blood tests. If you develop any symptoms of liver damage, be sure to talk with your doctor right away. If you have symptoms of liver damage or if your blood tests are showing possible liver damage, your doctor may recommend that you stop using Avonex.

Depression

Some people taking Avonex developed depression, mood changes, or suicidal thoughts or behaviors during treatment. Depression was a common side effect of this medication. But rates of suicidal thoughts or behaviors were rare.

Symptoms of these side effects can include:

What might help

Before you start taking Avonex, tell your doctor if you have any history of depression, mood disorders, or suicidal thoughts or behaviors. They may monitor you more often than usual if you have a history of mental health conditions.

If you do develop any of the symptoms mentioned above, be sure to talk with your doctor or caregiver right away. In some cases of suicidal thoughts or behaviors, you may need to visit an emergency room.

Your doctor will usually have you stop taking Avonex if you develop depression, mood changes, or suicidal thoughts or behaviors. Some people reported that their depression symptoms eased after stopping treatment with Avonex.

Suicide prevention

If you think someone is at immediate risk of self-harm or hurting another person:

  • Call 911 or your local emergency number.
  • Stay with the person until help arrives.
  • Remove any guns, knives, medications, or other things that may cause harm.
  • Listen, but don’t judge, argue, threaten, or yell.

If you or someone you know is considering suicide, get help from a crisis or suicide prevention hotline. Try the National Suicide Prevention Lifeline at 800-273-8255.

Your doctor will explain how you should use Avonex for multiple sclerosis (MS) and clinically isolated syndrome (CIS). They’ll also explain how much to inject and how often. Be sure to follow your doctor’s instructions. Below are commonly used dosages, but always take the dosage your doctor prescribes.

Taking Avonex

Avonex is a liquid solution that you inject into a certain muscle.

Avonex comes in two forms: a single-use prefilled syringe and an autoinjector. Each form contains 30 micrograms (mcg) of medication in 0.5 milliliters (mL) of solution. Either device should be used only once. So once you inject your Avonex dose, you should discard the syringe or autoinjector as directed.

Before you start using Avonex, your doctor or another healthcare professional will teach you how to use the syringe or autoinjector. This way, you can learn how to self-inject or have a caregiver inject the drug for you. Be sure to inject your Avonex dose exactly as your doctor prescribes.

Avonex injection sites

You’ll inject Avonex into the muscle of your upper, outer thigh. You should change injection sites with each dose. This helps prevent your skin from becoming irritated.

You shouldn’t inject your dose of Avonex into skin that’s red, a deeper color than usual, or bruised. You also shouldn’t inject the drug into skin that’s broken, scarred, or infected.

Dosage

You’ll usually inject Avonex once weekly. The dosing schedule for the drug increases over the course of a 4-week period. Your doctor will discuss your specific dosing frequency with you before your first dose.

When you first start taking Avonex, your doctor will usually start you at a low dosage. Here’s the standard dosing for MS and CIS:

  • Week 1: one 7.5-mcg injection
  • Week 2: one 15-mcg injection
  • Week 3: one 22.5-mcg injection
  • Week 4 and beyond: one 30-mcg injection (this is known as the maintenance dosage)

Taking Avonex with other drugs

If you experience side effects from Avonex, your doctor may recommend taking certain medications before your dose to help prevent the side effects. These medications may include acetaminophen (Tylenol) and diphenhydramine (Benadryl). Taking these medications before your dose may decrease your risk for certain side effects, such as fever or flu-like symptoms.

In some cases, your doctor may recommend that you use Avonex with other medication for MS or CIS. For example, if your MS symptoms get worse during treatment, your doctor may recommend taking a steroid medication with Avonex. The steroid may help ease nerve swelling.

Talk with your doctor about your treatment for MS before starting Avonex. They’ll be able to advise you on whether or not you should take other medications with Avonex.

Questions about taking Avonex

  • What if I miss a dose of Avonex? If you miss your dose of Avonex, take it as soon as you remember. But don’t take it if it’s almost time for your next dose. In that case, you’ll likely skip the missed dose and continue on with your regular dosing schedule. If you have any questions about when to take your next dose of Avonex after a missed dose, talk with your doctor or pharmacist. They’ll be able to recommend the best schedule for you moving forward.
  • Will I need to use Avonex long term? If Avonex works to help ease your symptoms, you’ll usually use the drug long term.
  • How long does Avonex take to work? Avonex may begin working to help prevent an MS relapse as soon as you take your first dose. (A relapse is a time of new or worsening symptoms.) But because Avonex drug works to help prevent relapses, you may not even notice that the drug is working. If you have questions about how to tell if Avonex is working for you, talk with your doctor.
Questions for your doctor

You may have questions about Avonex and your treatment plan. It’s important to discuss all your concerns with your doctor.

Here are a few tips that might help guide your discussion:

  • Before your appointment, write down questions such as:
    • How will Avonex affect my body, mood, or lifestyle?
  • Bring someone with you to your appointment if doing so will help you feel more comfortable.
  • If you don’t understand something related to your condition or treatment, ask your doctor to explain it to you.

Remember, your doctor and other healthcare professionals are available to help you. And they want you to get the best care possible. So don’t be afraid to ask questions or offer feedback on your treatment.

Avonex is used to treat certain forms of multiple sclerosis (MS).

MS is a condition that affects the nerves that connect your brain and spinal cord. MS causes your immune system to mistakenly attack the covering of your nerve fibers. This means that your brain can’t communicate well with the rest of your body. Some symptoms of MS may include:

To be specific, Avonex is used to treat relapsing forms of MS. (A relapse is a time of new or worsening symptoms.) Avonex is used to treat the following in adults:

  • Relapsing-remitting MS. In this form of MS, you have times when your MS symptoms worsen then get better. “Remitting” means getting better.
  • Active secondary progressive MS. In this form of MS, symptoms continue to worsen without getting better.
  • Clinically isolated syndrome (CIS). This is an episode of symptoms similar to those of MS, and it lasts for 24 hours or more. CIS isn’t a true form of MS, and it may or may not become MS.

It’s not known how Avonex works to ease symptoms. But it’s believed that the drug may change how your immune system works and decrease inflammation (swelling and damage). This may then help relieve your symptoms.

If you have questions about whether or not Avonex is right for you, talk with your doctor.

Find answers to some commonly asked questions about Avonex.

Are there side effects related to stopping Avonex treatment?

No, you shouldn’t experience any side effects from stopping Avonex treatment. Avonex is not known to cause symptoms of withdrawal.

But when you stop treatment with Avonex, your symptoms of multiple sclerosis (MS) or clinically isolated syndrome (CIS) may worsen. This is because Avonex was working to help ease your symptoms. If you stop taking the drug, it’s possible that your symptoms may get worse.

If you have any questions about possible side effects when you end Avonex treatment, talk with your doctor.

At what temperature does Avonex need to be stored? Does it need to be refrigerated?

You should store Avonex in the refrigerator (36°F to 46°F/2°C to 8°C). Keep the syringes or autoinjectors in their original carton so that they’re protected from light.

When you’re ready for your dose of Avonex, take the medication out of the refrigerator. You should do this about 30 minutes before your injection. Let Avonex come to room temperature before you inject it. It’s important that you don’t use any other heat sources, such as a microwave, to warm up the medication.

Once you have removed Avonex from the refrigerator, you should use it within 7 days. You shouldn’t put the medication back in the refrigerator once it has come to room temperature.

You may also wonder how long Avonex can be unrefrigerated. You can keep the medication at room temperature (up to 77°F/25°C) for up to 7 days. Be sure that you don’t expose Avonex to high temperatures. Doing so may make the medication less effective than usual.

If you have any questions about storing Avonex, talk with your doctor or pharmacist.

How does Avonex work?

It’s not known how Avonex works to ease symptoms of MS and CIS. But it’s believed that the drug may change how your immune system works and decrease inflammation (swelling and damage). This may then help relieve your symptoms.

For more information on how Avonex works, see this article. You can also talk with your doctor or pharmacist.

Is weight gain or weight loss a side effect of Avonex?

No, weight gain and weight loss were not side effects that were reported in studies of people taking Avonex.

But in some cases, weight change can be a symptom of other side effects of Avonex. For example, if you develop heart failure due to Avonex, you may gain weight. Changes in your thyroid is another possible side effect of Avonex. And thyroid changes may cause weight gain or weight loss.

If you notice any unexpected changes in weight while you’re taking Avonex, be sure to talk with your doctor. They can help determine the cause.

Can I get a flu shot if I’m using Avonex?

According to guidelines from the American Academy of Neurology, if you have MS, you should get a flu shot each year. But if your doctor advises against it, you shouldn’t get the shot.

If you have more questions about flu shots while you’re taking Avonex, talk with your doctor.

The medications Avonex and Rebif are both approved to treat relapsing forms of multiple sclerosis. (With these forms, you may have new or worsening symptoms.) Both of the drugs contain the active ingredient interferon beta-1a. But even though these drugs are similar, they also have many differences.

If you’d like to know more about how these drugs compare, see this detailed breakdown. And be sure to talk with your doctor about which drug is right for you.

Before considering treatment with Avonex, talk with your doctor about all your medications and any physical or mental health conditions you have.

Interactions

Taking medications, vaccines, foods, and other things with a certain drug can affect how the drug works. These effects are called interactions.

Before taking Avonex, be sure to tell your doctor about all medications you take, including prescription and over-the-counter types. Also describe any vitamins, herbs, or supplements you use. Your doctor or pharmacist can tell you about any interactions these items may cause with Avonex.

Interactions with drugs or supplements

There are no known interactions between Avonex and other drugs or supplements. However, it’s still important to talk with your doctor about any other drugs or supplements that you’re taking.

Warnings

Avonex may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you use Avonex. Factors to consider include those in the list below.

  • Depression, mood disorders, or suicidal thoughts. Avonex may cause you to develop depression, mood changes, or suicidal thoughts or behaviors. If you have or had any of these mental health conditions, talk with your doctor before starting Avonex treatment. This is because taking Avonex may make your mental health condition worse. Your doctor may recommend more frequent monitoring while you use Avonex, or a different treatment option for you.
  • Liver problems. Avonex may cause you to develop liver damage. If you already have liver damage, Avonex may make it worse. Before using Avonex, be sure to tell your doctor about any liver problems that you have. They may monitor you more often than usual to watch for signs of liver damage. Or your doctor may recommend a different medication for you.
  • Allergic reaction. If you’ve had an allergic reaction to Avonex or any of its ingredients, including rubber latex, you shouldn’t use Avonex. Ask your doctor what other medications are better options for you.
  • Congestive heart failure or other heart problems. In rare cases, Avonex may cause heart failure. If you already have heart failure or other heart problems, taking Avonex may make your heart problems worse. Your doctor may monitor your heart health more often than usual or recommend a different treatment option for you.
  • Bleeding problems or blood clots. Avonex can decrease the amount of certain blood cells in your body. This may increase your risk for bleeding or clotting. If you have or had a bleeding problem or have had blood clots, be sure to tell your doctor before using Avonex. They may monitor your blood more often than usual or recommend a different treatment option for you.
  • Low blood cell counts. If you have low blood cell counts, taking Avonex may make these counts worse. Be sure to tell your doctor if you have or had low blood cell counts. They may monitor your blood more frequently than usual or recommend a different treatment option for you.
  • Autoimmune disorders, such as thyroid problems. Multiple sclerosis is a kind of autoimmune disorder. Tell your doctor about any other autoimmune disorders you have, such as thyroid problems. Sometimes, Avonex may make other autoimmune disorders worse. Your doctor may check your symptoms more often than usual to see if they’re getting worse. Or they may recommend a different treatment.
  • Seizure disorders. Some people taking Avonex developed seizures. If you have any seizure disorders, you may be at an increased risk for having a seizure while using the medication. Tell your doctor if you have or had a seizure disorder. They may recommend a different treatment option for you.

Avonex and alcohol

Alcohol and Avonex may both cause liver damage. So drinking alcohol while you’re taking Avonex may further increase your risk for liver damage.

Talk with your doctor about how much, if any, alcohol is safe to drink during your treatment with Avonex. If it’s hard for you to avoid alcohol, they may recommend a different treatment option for you.

Pregnancy and breastfeeding

Here’s some information on whether Avonex should be used while pregnant or breastfeeding.

Pregnancy. It is not known if Avonex is safe to take while pregnant. This is because there haven’t been any studies of the drug during pregnancy.

Other interferon beta drugs have been tested during pregnancy with mixed results. (Avonex is a kind of interferon beta drug.)

If you’re pregnant or planning to become pregnant, talk with your doctor before taking Avonex. They may recommend a different treatment option for you.

Breastfeeding. It is not known how much Avonex may pass into breast milk or what effects the drug may have on a child who is breastfed.

If you’re breastfeeding or planning to, tell your doctor before starting Avonex treatment. They can help determine the risks and benefits of taking Avonex while you’re breastfeeding. They may also recommend a different medication.

Both the drugs Avonex and Gilenya are used to treat the same forms of multiple sclerosis. Both drugs also contain the active drug interferon beta-1a. Avonex and Gilenya have other similarities as well as differences. This may help you and your doctor determine which is the best option for you.

To learn more about how these drugs are similar and different, see this side-by-side comparison. Also, talk with your doctor about which medication they think is better for you.

Costs of prescription drugs can vary depending on many factors. These factors include what your insurance plan covers and which pharmacy you use. To find current prices for Avonex in your area, visit GoodRx.com.

If you have questions about how to pay for your prescription, talk with your doctor or pharmacist. You can also visit the Avonex manufacturer’s website to see if there are support options.

Don’t use more Avonex than your doctor prescribes. Using more than this can lead to serious side effects.

What to do in case you take too much Avonex

Call your doctor if you think you’ve used too much Avonex. You can also call 800-222-1222 to reach the American Association of Poison Control Centers, or use its online resource. However, if you have severe symptoms, immediately call 911 (or your local emergency number) or go to the nearest emergency room.

If you have more questions about Avonex, talk with your doctor. Examples of some specific questions that you may wish to ask include:

  • Am I at an increased risk for side effects if I’m also taking other medications for multiple sclerosis (MS)?
  • If a dosage of 30 micrograms (mcg) once weekly isn’t working for me, can my dose be changed?
  • What will happen if I become pregnant while I’m using Avonex?
  • How should I inject my dose of Avonex?

If you have other questions about Avonex, see this article about MS treatment options. The MS comparison chart may also help show which medications may be right for you.

If you have questions about MS, sign up for the MS newsletter.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.