Tysabri (natalizumab) is a brand-name prescription medication. It’s approved by the Food and Drug Administration (FDA) to treat the following conditions in adults:

If you and your doctor agree that Tysabri is working well for you, you’ll likely take the drug long term.

Here are some fast facts about Tysabri:

Like other drugs, Tysabri can cause side effects. Read on to learn about potential common, mild, and serious side effects. For a general overview of Tysabri, including details about its uses and how it’s given, see this article.

Tysabri can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Tysabri in clinical trials. These side effects can vary depending on which condition the drug is being taken to treat.

More common side effects in people receiving Tysabri treatment for multiple sclerosis include:

More common side effects in people receiving Tysabri treatment for Crohn’s disease include:

* For more information about this side effect, see “Side effect specifics” below.

Mild side effects can occur with Tysabri. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Tysabri’s prescribing information.

Mild side effects that have been reported with Tysabri include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while receiving Tysabri and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.

While rare, treatment with Tysabri may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to Tysabri’s prescribing information.

If you develop serious side effects while receiving Tysabri, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported and their symptoms include:

* Tysabri has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA).
† To learn more about this side effect, see the “Side effect specifics” section below.

Tysabri may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

How long do Tysabri’s side effects last?

Most side effects caused by Tysabri are mild and don’t last for long. They tend to be temporary, lasting a few days to weeks. However, there are cases where Tysabri’s mild side effects don’t go away.

Rarely, Tysabri can cause serious side effects that lead to long-term problems. For example, serious eye infections have led to blindness in clinical trials. This was very rare, however. Tysabri can also cause liver damage. This can be severe and cause long-term problems, including liver failure. (To learn more, see “Side effect specifics” below.)

If you have questions about how long side effects last with Tysabri treatment, be sure to talk with your doctor or pharmacist. You should contact your doctor right away if you develop symptoms of a serious side effect while having Tysabri treatment. Or, if your symptoms feel life threatening, call 911 or seek emergency medical help.

Are there any side effects that may occur after long-term treatment with Tysabri?

Yes, long-term treatment with Tysabri can raise your risk of certain side effects, such as serious infection. This includes a serious brain infection called progressive multifocal leukoencephalopathy (PML).

Having Tysabri treatment for a long time, especially for 2 years or more, raises your risk of PML. In fact, Tysabri has a boxed warning for this side effect. This is the most serious warning from the Food and Drug Administration (FDA). For more information on PML and Tysabri, see “Side effect specifics” below.

There’s also a risk of developing other serious infections at any time during Tysabri treatment. This is possible because Tysabri weakens your immune system once you start treatment. So you may have a higher risk of infection at any time, including in the long term. For example, severe herpes infections have been reported several years after people started Tysabri treatment.

If you have additional questions about side effects that occur after long-term treatment with Tysabri, talk with your doctor or pharmacist.

Do Tysabri’s side effects include hair loss?

No, hair loss isn’t a known side effect of Tysabri treatment. Hair loss wasn’t reported by people receiving Tysabri in clinical trials.

Other medications prescribed to treat multiple sclerosis, such as mitoxantrone and Aubagio (teriflunomide), are known to cause hair loss as a side effect. And Crohn’s disease, which Tysabri is also prescribed to treat, can cause hair loss.

If you’re concerned about hair loss, talk with your doctor or pharmacist. They can review your treatment plan to help determine the cause of your hair loss. They may recommend a treatment for hair loss. Or may suggest trying other treatments besides Tysabri for your condition.

Learn more about some of the side effects that Tysabri may cause.

Weight gain

Weight gain is a possible side effect of Tysabri. However, this side effect was rarely reported in clinical trials. Weight loss was also a rare side effect in people who took Tysabri.

It’s important to note that weight changes can happen in people with multiple sclerosis (MS) or Crohn’s disease. Weight gain is more common with MS, while weight loss is more common with Crohn’s disease.

What you can do

Talk with your doctor if you experience weight gain or are concerned about weight changes while receiving Tysabri. They can discuss ways to help you maintain a weight that’s healthy for you.

Fatigue

Fatigue was a common side effect of Tysabri reported in clinical trials. However, it was typically mild.

Symptoms of fatigue include:

  • feeling exhausted most or all of the time, even after a good night’s sleep
  • trouble carrying out everyday activities, such as work or household chores

Having MS or Crohn’s disease can cause fatigue. However, fatigue can also be a symptom of serious side effects caused by Tysabri, including liver damage.

What you can do

In most cases, Tysabri causes mild fatigue that usually goes away on its own. However, if you have fatigue that bothers you or doesn’t go away, talk with your doctor. They may have you stop Tysabri treatment and recommend a different treatment for your condition.

Liver damage

While rare, liver damage has been reported in clinical trials of Tysabri. In extreme cases, some people needed a liver transplant due to this side effect.

Liver damage can occur as soon as a few days after your first dose of Tysabri. And it can start after you’ve taken Tysabri for some time.

Symptoms of liver damage caused by Tysabri can include:

What you can do

Contact your doctor right away if you have symptoms of liver damage while having Tysabri treatment. Your doctor will likely order blood tests that check for signs of liver damage. They will have you stop Tysabri treatment if they confirm you have liver damage from taking the drug.

Serious brain infection

Tysabri has a boxed warning* about a rare but serious brain infection called progressive multifocal leukoencephalopathy (PML). This is a serious warning from the Food and Drug Administration (FDA). Boxed warnings alert healthcare professionals and patients about the most serious side effects a drug may cause.

PML is caused by the John Cunningham (JC) virus. This is a common virus that doesn’t cause symptoms in most people who have it. However, it can cause brain infection in people with weakened immune systems. This includes people receiving Tysabri treatment. In clinical trials, PML was a very rare side effect of the drug.

Symptoms of PML can include:

  • changes in thinking
  • clumsiness
  • confusion
  • memory problems
  • personality changes
  • weakness of one side of the body that gets worse over time
  • vision changes

Although it’s rare, PML is a life threatening infection that often leads to disability and can even cause death. PML can occur at any time while receiving Tysabri treatment. It can also happen after you stop treatment. You may be more likely to develop PML if you:

  • have taken an immunosuppressant (a drug that weakens your immune system) in the past
  • are receiving Tysabri treatment long term, particularly for more than 2 years
  • are receiving Tysabri treatment with certain other medications for MS or Crohn’s disease

What you can do

Before you start Tysabri treatment, your doctor will review your risk factors for PML. Your doctor may order a blood test to see if you already have the JC virus. They may also order magnetic resonance imaging (MRI) scans of your brain to see if you develop PML during treatment.

There’s no known cure for PML. Your doctor will monitor you for PML while you receive Tysabri. You’ll also need to watch for symptoms for at least 6 months after your last dose of Tysabri. If you notice symptoms of PML, contact your doctor immediately.

* Because of the risk of PML, Tysabri is only available through a special program called the TOUCH® Prescriber Program. You can learn more about the program by checking this website or talking with your doctor.

Allergic reaction

As with most drugs, Tysabri can cause an allergic reaction in some people. For more information on this side effect, see the drug’s prescribing information.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

Infusion reactions, such as dizziness, low blood pressure, itchiness, shortness of breath, or chest pain, may also occur. These reactions usually occur within hours after the start of your Tysabri infusion.

What you can do

For mild symptoms of an allergic or infusion reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep receiving Tysabri treatment. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

During your infusion of Tysabri, your doctor will monitor you for reactions to the drug. If you have symptoms of an allergic reaction or infusion reaction, your infusion may be paused so that your doctor can treat your symptoms.

The treatments will depend on your infusion reaction symptoms. Your doctor may give you a pain reliever, such as ibuprofen, to treat mild symptoms such as headache or joint stiffness. For a mild allergic reaction, they may recommend taking Benadryl (diphenhydramine). Other reactions may require different treatments. To learn more, talk with your doctor.

There are certain precautions for Tysabri treatment to consider before taking the medication. This includes a boxed warning from the Food and Drug Administration (FDA).

Boxed warning: Serious brain infection

This drug has a boxed warning about a serious brain infection called progressive multifocal leukoencephalopathy (PML). This is a serious warning from the FDA. For details, see the “Side effect specifics” section above.

Other precautions

Be sure to talk with your doctor about your health history before you take Tysabri. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

Weakened immune system. Tysabri can weaken the immune system. This can increase your risk of infection, including serious infection. Certain other medical conditions can also weaken your immune system. These include HIV or AIDS, leukemia, lymphoma, or having an organ transplant. If you have a weakened immune system, talk with your doctor about other treatments that may be safer for you.

Current infection. If you have a current infection, your doctor will likely not prescribe you Tysabri. The drug weakens your immune system, which may make an infection harder to treat. Your doctor will likely wait to prescribe Tysabri to you until after the infection is treated.

Allergic reaction. If you’ve had an allergic reaction to Tysabri or any of its ingredients, your doctor will likely not prescribe Tysabri. Ask your doctor what other medications may be better options for you. (For more information, see “Side effect specifics” above.)

Alcohol with Tysabri

There’s no known interaction between drinking alcohol and Tysabri treatment.

However, that doesn’t necessarily mean it’s safe to drink alcohol while receiving Tysabri treatment. For more information, check out this article. You can also talk with your doctor or pharmacist.

Pregnancy and breastfeeding while receiving Tysabri treatment

It’s not known whether it’s safe to take Tysabri while pregnant. The medication hasn’t been studied during pregnancy. However, there have been reports of side effects, such as low red blood cell levels, in newborns who were exposed to the drug before birth.

If you’re pregnant or planning to become pregnant, talk with your doctor. They’ll advise you on the risks and benefits of receiving Tysabri treatment during pregnancy.

Tysabri is known to pass into breast milk. However, it’s not known whether this causes problems with breastfeeding or side effects in a child who is breastfed. Talk with your doctor about the risks and benefits and other possible feeding options for your child.

Treatment with Tysabri can cause mild and serious side effects. Most side effects aren’t common, but if they do happen, they tend to be mild.

However, Tysabri can cause serious side effects in rare cases. Talk with your doctor if you develop side effects that are serious or bothersome. For more information, see “Side effect specifics” above.

If you’d like to learn more about Tysabri, talk with your doctor or pharmacist. They can help answer any questions you have about side effects of taking the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

Disclaimer: Medical News Today 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 another 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.