If you have multiple sclerosis (MS), clinically isolated syndrome (CIS), 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 certain kinds of MS, CIS, 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.

Usually Tysabri is given once every 4 weeks. It is meant to be used for a long time.

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

Tysabri can cause mild or serious side effects. Continue 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) or clinically isolated syndrome (CIS) include:

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

Mild side effects have been reported with Tysabri.

The side effects explained section is where you can learn more about this side effect.

“These side effects should be temporary. Some may be easy to manage. If you have any symptoms that bother you, talk to your doctor or pharmacist. Unless your doctor recommends it, don’t stop using Tysabri.”

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.

There have been serious side effects with Tysabri.

* 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 taking Tysabri, call your doctor. If the side effects seem life threatening or if you think you have a medical emergency, immediately call the emergency number.

There are frequently asked questions about Tysabri.

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), clinically isolated syndrome (CIS), 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 are having hair loss, talk to your doctor. They may suggest ways to manage hair loss.

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.)

“The symptoms of multiplesclerosis or crosicillosis may return if Tysabri treatment is stopped. If your doctor doesn’t change you to a new treatment, this is especially so.”

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 will discuss the next steps with you.

Can using Tysabri affect my teeth?

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

There are signs of an infection. Tysabri makes your immune system less effective at fighting infections. 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, you should contact your dentist. It is important to have dental problems treated as soon as possible.

Will Tysabri affect my menstrual cycle?

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

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

If The 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.

How long does Tysabri stay in my system?

How long Tysabri stays in your system is based on your dosage and the condition you’re taking the drug for.

If you take Tysabri for MS or CIS, the drug usually stays in your body for 35 to 75 days (about 6 to 11 weeks), depending on your dosage. If you take Tysabri for Crohn’s disease, it’ll stay in your system for 15 to 85 days (approximately 2 to 12 weeks). The precise amount of time varies depending on your dosage.

You can talk to your doctor or pharmacist about how long Tysabri stays in your system.

Tysabri may cause some side effects.

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) or clinically isolated syndrome (CIS). 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 or CIS, 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, talk to your doctor. They can help you identify and manage factors that could affect your weight. They may suggest diet or exercise changes to maintain a moderate weight.

Infusion-related side effects

There are possible reactions with Tysabri treatment. There are side effects that occur within 2 hours after a Tysabri injection.

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, a severe allergic reaction to Tysabri can be seen in an infusion reaction.

People who take breaks from Tysabri treatment are more likely to have severe allergic reactions. After taking a break from Tysabri treatment, your risk of reactions may be higher. It is important to receive your Tysabri treatments on a regular schedule.

Only a healthcare professional can give you a Tysabri treatment. They will watch you during the hour-long infusion. They will keep an eye on you for at least an hour after each Tysabri injection.

Symptoms of infusion-related reactions

Depending on whether you are being treated with Tysabri for multiplesclerosis, or with other diseases, the symptoms of the infusion-related reactions can vary. There are symptoms related to vinod.

  • There is a throbbing head.
  • dizziness
  • fatigue (low energy)
  • There are bees. (itchy welts on your skin)
  • It was itching.
  • It is cold.
  • flushing (temporary warmth, redness, or deepening of skin color)

There are symptoms of a severe reaction to an injection.

What might help

For most people, infusion-related side effects such as There is a throbbing head. or dizziness are mild. They should go away on their own.

If you notice any of the above symptoms, immediately alert your healthcare professional. If there are any symptoms that are indicative of an allergic reaction, they will stop the infusion.

If you are concerned about the risks of the infusion, talk to your doctor.

Progressive multifocal leukoencephalopathy (PML)

Tysabri has a boxed warning about the risk of 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 risk of getting PML with Tysabri is very low. People with all three 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 can get worse over time.

What might help

If you have JCV, your doctor may test your blood for it.

After your last injection, your doctor will monitor you for symptoms of PML. If you develop any symptoms, tell your doctor. They will likely stop you from receiving Tysabri at the first sign of PML.

If you have questions about your risk of PML, talk to your doctor. They will discuss the risks and benefits of the drug with you.

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.

There are symptoms of liver damage.

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

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

What might help

Blood tests will be used by your doctor to monitor the health of your body.

If you notice any of the symptoms, you should immediately tell your doctor. They will likely have you stop or pause your 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 or CIS, 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 or CIS. These effects weren’t seen in the studies of the drug for Crohn’s disease.

Depression can last for 2 weeks or longer.

  • I feel sad or powerless.
  • Your interest in your favorite activities has been lost.
  • Changes in appetite or sleep patterns
  • There is not enough energy or motivation.

What might help

“If you have depression, you should tell your doctor about it. They may watch you more closely during Tysabri treatment to make sure you don’t get depressed.”

If you notice depression symptoms, talk to your doctor. They may recommend a treatment plan.

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

If you notice a change in your behavior or mood, it is important to tell your doctor. If you have thoughts of harming yourself, seek emergency medical care.


If you think someone is at risk of self-injury or hurting another person.

  • You can call your local emergency number.
  • Stay with the person until help arrives.
  • Guns, knives, medications, and other things should be removed.
  • “Don’t judge, argue, threaten, or yell.”

If you or someone you know is considering suicide, you should get help from a hotline. The National Suicide Prevention Hotline is 800-273-8255.

Allergic reaction

Tysabri can cause an allergic reaction in some people.

Mild or serious symptoms can be present.

  • skin There is a rash.
  • It is itchy.
  • flushing (temporary warmth, redness, or deepening of skin color)
  • “It’s swelling under your skin, usually in your lips, hands, or feet.”
  • It can be hard to breathe if you have swelling of your mouth, tongue, or throat.

What might help

If you have mild symptoms of an allergic reaction, such as a mild There is a 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 will decide if you should continue using it.

If you have symptoms of a severe allergic reaction, such as breathing problems 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

Keep notes on any side effects you have during your Tysabri treatment. You can share this information with your doctor. This is helpful when you are starting to use a combination of treatments.

Side effect notes can include things.

  • What dose of drug did you take when you had the side effect?
  • How soon after starting that dose did you experience side effects?
  • What were your symptoms after the side effect?
  • How did it affect your daily activities?
  • What other drugs were you taking?
  • Other information is important to you.

Sharing notes with your doctor will help him learn more about how Tysabri affects you. If needed, your doctor can use this information to adjust your treatment plan.

Tysabri may not be safe in certain situations. There are possible warnings for this drug.

Boxed warning: Progressive multifocal leukoencephalopathy

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

PML is a rare but serious brain infection and may increase your risk of receiving Tysabri.

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 have had PML in the past, you should not use Tysabri.

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

Other warnings

If you have a medical condition that affects your health, Tysabri may not be right for you. Before you receive Tysabri, you should talk to your doctor about your health history. The list has factors to consider.

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

Discuss your health history with your doctor. They will be able to tell you if it is safe 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 There is a throbbing head., nausea, and liver damage, and so can alcohol.

It is possible that drinking alcohol may make your condition worse. Talk to your doctor about how much alcohol you should drink.

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. But there have been reports of certain side effects in newborns who were exposed to Tysabri before birth. These side effects include low red blood cells and low platelets.

It is not known if it is safe to give Tysabri to breastfeeding mothers. Tysabri can be found in human breast milk. There is no research done to learn about the effects of Tysabri on children who are breastfed.

Before starting Tysabri, you should tell your doctor if you are pregnant or breastfeeding. If you plan to become pregnant or breastfeeding, you should talk to your doctor. They can discuss the risks and benefits of doing so with you.

“Some people have side effects from Tysabri. 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 is best to talk to your doctor about any questions you have about Tysabri.”

Some questions you may want to ask your doctor.

  • “Do my health conditions increase 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?
  • What steps can I take to help prevent infections such as vaginitis during Tysabri treatment?

For information and tips on managing multiple sclerosis (MS), consider signing up for Healthline’s MS newsletter or joining Bezzy MS. For information about inflammatory bowel disease (IBD), such as Crohn’s disease, you can sign up for our IBD newsletter and find resources in Bezzy IBD.


Does taking certain medications increase my risk of side effects?



Taking Tysabri with certain medications can increase your risk of side effects such as infections or progressive multifocal leukoencephalopathy (PML). These medications can include:

If you take medications that suppress your immune system or TNF-alpha inhibitors, you shouldn’t receive Tysabri.

Also, if you’re taking a steroid, such as prednisone, the dose should be gradually decreased before you receive Tysabri.

Before starting Tysabri treatment, you should tell your doctor about any medications you are taking.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

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.