If you have multiple sclerosis (MS) or Crohn’s disease, your doctor might suggest Tysabri (natalizumab) as a treatment option. Along with other factors to consider, you may be wondering about the medication’s possible side effects.

Tysabri is a prescription biologic drug that’s used to treat MS and Crohn’s disease in adults.

A healthcare professional will give you Tysabri as an intravenous (IV) infusion. This is an injection that slowly drips into your vein over a period of time. Tysabri infusions usually take about an hour.

Tysabri is usually given once every 4 weeks. It’s meant to be used as a long-term treatment.

For more information about Tysabri, including details about its uses, see this in-depth article on the drug.

Like other drugs, Tysabri infusions can cause mild or serious side effects. Keep reading to learn more.

Some people may experience mild or serious side effects during their Tysabri treatment. These side effects can vary depending on what condition the drug is being used to treat. These are just a few of the more common side effects reported by people who took Tysabri in studies.

More common side effects in people receiving Tysabri for multiple sclerosis (MS) include:

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

Examples of mild side effects that have been reported with Tysabri include:

* To learn more about this side effect, see the “Side effects explained” section below.

In most cases, these side effects should be temporary. Some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. Don’t stop using Tysabri unless your doctor recommends it.

Tysabri may cause mild side effects other than the ones listed above. See the drug’s prescribing information for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Tysabri, visit MedWatch.

Serious side effects that have been reported with Tysabri 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, see the “Side effects explained” section below.
† To learn more about this side effect, see the “Side effects explained” section below.

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

Read some frequently asked questions and answers about Tysabri’s side effects.

Does Tysabri cause hair loss?

If you have hair loss during treatment with Tysabri, it’s probably not caused by the drug. In studies, hair loss wasn’t a side effect reported in people receiving Tysabri.

Keep in mind that Tysabri is used to treat multiple sclerosis (MS) or Crohn’s disease. Hair loss can be triggered by other factors related to these conditions, such as stress and other prescribed medications.

Also, some people with Crohn’s disease have trouble absorbing essential vitamins and minerals from their diet. This can lead to nutrient deficiencies, another possible reason for hair loss.

If you’re having hair loss, talk with your doctor. They may suggest other causes of hair loss and ways to manage them.

Will I experience withdrawal symptoms if I stop my Tysabri treatment?

Stopping Tysabri treatment shouldn’t cause withdrawal symptoms. (These are side effects that can happen when you stop taking a drug that your body has become dependent on.)

But stopping Tysabri treatment may cause the symptoms of MS or Crohn’s disease to return. This is especially so if your doctor doesn’t switch you to a new treatment.

Some research shows that stopping Tysabri treatment for MS may cause rebound effects. This means that stopping drug treatment may cause MS to progress (get worse) in some people. More research is needed to learn how often this occurs. A study showed that receiving steroid infusions after ending Tysabri treatment may reduce the possibility of rebound effects.

If you and your doctor decide that Tysabri treatment is no longer right for you, they’ll discuss the next steps with you.

Can using Tysabri affect my teeth?

Yes, Tysabri can cause toothaches or tooth infections in some people. These teeth-related side effects occurred during studies of the drug, but they weren’t common.

Toothaches can be a symptom of an infection. Tysabri weakens your immune system’s ability to fight off infections. So Tysabri increases your risk of infections, including those of the teeth and mouth.

Toothache pain is usually a sign of a cavity or gum infection. If not treated promptly, cavities can lead to an abscessed tooth (a tooth that has a pocket of pus). Infection from the abscessed tooth can spread into your bloodstream and become serious.

To help prevent teeth-related side effects, be sure to use good dental hygiene during Tysabri treatment. This includes regular brushing, flossing, and visiting your dentist and dental hygienist for routine checkups and cleanings.

If you notice tooth pain or sensitivity during Tysabri treatment, see your dentist right away. It’s important to have dental problems treated as soon as possible before severe infections develop.

Will Tysabri affect my menstrual cycle?

It’s possible. During studies of the drug, some people had menstrual cycle changes with Tysabri treatment.

Menstrual cycle changes with Tysabri may include painful periods, missed periods, or irregular cycles.

If menstrual cycle changes become bothersome or don’t go away, talk with your doctor. They’ll be able to suggest ways to manage your symptoms.

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

Weight gain or weight loss

In studies, some people who took Tysabri had weight gain or weight loss. Overall, weight changes weren’t common, and weight gain was reported just as often as weight loss. It isn’t known how much weight people gained or lost during treatment.

Note that weight changes were only seen in studies of the drug as a treatment for multiple sclerosis (MS). These side effects weren’t seen in the studies of the drug for Crohn’s disease.

This difference is likely because it’s common to experience weight fluctuations with MS. Symptoms of MS, such as fatigue (low energy) and weakness, can sometimes make it tough to exercise regularly. Medications used to treat MS symptoms can also play a role in weight changes.

What might help

If you notice weight changes that concern you during Tysabri treatment, talk with your doctor. They may be able to help you identify and manage factors that could be affecting your weight. They may also suggest diet or exercise changes to maintain a moderate weight with your condition.

Infusion-related side effects

Infusion-related reactions may happen with Tysabri treatment. Infusion-related reactions are side effects that occur within 2 hours after the start of a Tysabri infusion.

A healthcare professional will give you Tysabri as an intravenous (IV) infusion. This is an injection that slowly drips into your vein over a period of time. Tysabri infusions usually take about an hour.

In studies, infusion-related side effects were more common in people treated with Tysabri than in people who received a placebo. (A placebo is a treatment that doesn’t contain an active drug.)

In rare cases, infusion reactions can be a sign of a severe allergic reaction to Tysabri.

Severe allergic reactions seem to be more common in people who take breaks from Tysabri treatment and then start receiving it again. Your risk of infusion-related reactions may be higher with your first infusion after taking a break from Tysabri treatment. It’s important to receive your Tysabri treatments on a regular schedule and not miss your infusion appointments.

Because of the risk of infusion-related reactions, only a healthcare professional can give you a Tysabri treatment. They’ll monitor you during the hour-long infusion for any reactions. They’ll continue to monitor you for at least an hour after each Tysabri infusion.

Symptoms of infusion-related reactions

The symptoms of infusion-related reactions can vary based on whether you’re being treated with Tysabri for MS or Crohn’s disease. Infusion-related symptoms can include:

  • headache
  • dizziness
  • fatigue (low energy)
  • hives (itchy welts on your skin)
  • itching
  • shivering
  • flushing (temporary warmth, redness, or deepening of skin color)

Symptoms of a severe infusion related reaction include:

What might help

For most people, infusion-related side effects such as headache or dizziness are mild. They should go away on their own.

If you notice any of the above symptoms during or after receiving a Tysabri infusion, alert your healthcare professional right away. If any symptoms occur that could be a sign of an allergic reaction, they’ll likely stop the infusion.

If you’re concerned about your risk of infusion-related side effects, talk with your doctor.

Progressive multifocal leukoencephalopathy (PML)

Tysabri has a boxed warning for a rare brain infection called PML. This is the most serious warning from the Food and Drug Administration (FDA). A boxed warning alerts doctors and patients about drug effects that may be dangerous.

PML is a rare but serious brain infection that’s been reported with Tysabri use. There’s no known cure for PML. Infection with PML usually leads to severe disability, such as being unable to walk, or even death. Other medications used to treat MS have also been linked to an increased risk of PML.

The chance of getting PML with Tysabri is rare. But people with all three of the following factors have the highest risk of developing PML:

It’s possible to develop PML during Tysabri treatment and up to 6 months after you stop receiving the drug. Because of the risk of PML, Tysabri is only available through a restricted program called TOUCH. Your doctor can tell you more about this program.

PML symptoms may get worse over days or weeks and can include:

What might help

Before starting Tysabri, your doctor may test your blood to check if you’ve been infected with JCV.

During treatment with Tysabri and for 6 months after your last infusion, your doctor will monitor you for symptoms of PML. If you develop any symptoms, tell your doctor right away. They’ll likely have you stop receiving Tysabri at the first possible sign of PML.

If you have questions about your risk of PML with Tysabri, talk with your doctor. They’ll discuss with you the possible risks and benefits of the drug for your condition.

Liver damage

Tysabri may increase the risk of liver damage. Although not seen during studies of Tysabri, this side effect has since been reported in some people receiving the drug.

Symptoms of liver damage can include:

  • jaundice (yellowing of the skin or whites of the eyes)
  • dark urine
  • nausea or vomiting
  • feeling weak or tired
  • itchy skin

Another sign of liver damage is increased liver enzymes, as seen in blood test results.

What might help

Before and during Tysabri treatment, your doctor will use blood tests to monitor the health of your liver.

If you notice symptoms of liver damage as listed above, tell your doctor right away. They’ll likely have you pause or stop Tysabri treatments to help determine the cause of your symptoms.

Depression, and suicidal thoughts and behaviors

Tysabri may cause depression as a side effect in some people. In studies of the drug as a treatment for MS, depression was a common side effect.

Depression is also a common symptom of MS.

Very rarely, suicidal thoughts and actions were reported during studies of Tysabri for MS. These effects weren’t seen in the studies of the drug for Crohn’s disease.

Symptoms of depression may last for 2 weeks or longer and can include:

  • feeling sad or hopeless
  • loss of interest in your favorite activities
  • changes in your usual appetite or sleep patterns
  • lack of energy or motivation

What might help

If you already have depression, be sure to tell your doctor before starting Tysabri. They may monitor you more carefully than usual during Tysabri treatment to watch for signs of worsening depression.

If you notice depression symptoms as described above, talk with your doctor. They may recommend a treatment plan to ease depression.

It may also be helpful to see a mental health expert, such as a psychologist or therapist. They can offer strategies to help manage the stresses of your condition.

It’s important to tell your doctor right away if you or someone close to you notices changes in your behavior or mood. If you have any thoughts of harming yourself, seek emergency medical care.

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.

Allergic reaction

Like most drugs, Tysabri can cause an allergic reaction in some people.

Symptoms can be mild or serious and can include:

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

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. To manage symptoms, they may suggest an over-the-counter antihistamine you take by mouth, such as Benadryl (diphenhydramine). Or they may recommend a product you apply to your skin, such as hydrocortisone cream.

If your doctor confirms you had a mild allergic reaction to Tysabri, they’ll decide if you should continue using it.

If you have symptoms of a severe allergic reaction, such as trouble breathing during or shortly after an infusion of the drug, tell your doctor right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you had a serious allergic reaction to Tysabri, they may have you switch to a different treatment.

Keeping track of side effects

During your Tysabri treatment, consider keeping notes on any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful to do when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of drug you were taking when you had the side effect
  • how soon after starting that dose you had the side effect
  • what your symptoms were from the side effect
  • how it affected your daily activities
  • what other medications you were also taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help your doctor learn more about how Tysabri affects you. Your doctor can use this information to adjust your treatment plan if needed.

In certain situations, it may not be safe to use Tysabri. Keep reading to learn more about possible warnings for this drug.

Boxed warning: Progressive multifocal leukoencephalopathy

Tysabri has a boxed warning for progressive multifocal leukoencephalopathy (PML). A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Receiving Tysabri may increase your risk of PML, a rare but serious brain infection.

Other factors may increase your risk of developing PML with Tysabri. These include using Tysabri for longer than 2 years, past treatment with drugs that weaken your immune system, and past infection with the John Cunningham virus (JCV). It’s important to discuss these risk factors with your doctor before starting Tysabri.

If you’ve had PML in the past, you should not use Tysabri.

To learn more, see the “Side effects explained” section above.

Other warnings

Tysabri 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 receive Tysabri. The list below includes factors to consider.

Weakened immune system. Tysabri can lower your immune system and its ability to fight off infections. If you already have a condition that weakens your immune system, such as HIV, Tysabri may further increase your risk of developing serious infections. Also, the use of certain medications, such as steroids, can weaken your immune system.

Be sure to discuss your health history and recent medications with your doctor. They’ll be able to advise you on whether it’s safe for you to receive Tysabri.

Allergic reaction. If you’ve had an allergic reaction to Tysabri or any of its ingredients, you shouldn’t receive Tysabri. Ask your doctor what other medications are better options for you.

Alcohol use and Tysabri

There are no known interactions between Tysabri and alcohol. But drinking alcohol during Tysabri treatment may increase your risk of side effects from the drug. For example, Tysabri can cause headache, nausea, and liver damage, and so can alcohol.

Drinking alcohol may also worsen the symptoms of your condition. Talk with your doctor about how much alcohol is safe for you to drink with your condition and medications.

Pregnancy and breastfeeding during Tysabri treatment

It’s not known whether Tysabri is safe for use during pregnancy. No studies have been done to look at the drug’s effects during pregnancy.

It’s also not known if it’s safe to receive Tysabri while breastfeeding. Studies show that Tysabri passes into human breast milk. But no studies have been done to learn about the effects of Tysabri on children breastfed by someone who took the drug.

If you’re pregnant or breastfeeding, tell your doctor before starting Tysabri. If you want to conceive or breastfeed, talk with your doctor. They can discuss with you the risks and benefits of doing so with your condition and current treatments.

Tysabri commonly causes mild side effects in some people. In rare cases, the drug can cause serious side effects. Learning about Tysabri’s possible side effects can help you decide if it’s the right choice for your condition. It’s best to talk with your doctor about any questions or concerns you have about Tysabri.

Here are some questions that you may want to ask your doctor:

  • Do my other health conditions or past medications raise my risk of Tysabri’s serious side effects?
  • I’m concerned about infusion-related side effects. Is there an alternative to Tysabri that’s available as a pill?
  • Is it safe to get vaccines during Tysabri treatment, or will this increase my risk of side effects?
  • What steps can I take to help prevent infections such as vaginitis during Tysabri treatment?

For information and tips on managing your condition, sign up for Healthline’s multiple sclerosis newsletter or IBD 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 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.