Natalizumab (sold under the name Tysabri) is a treatment for highly active relapsing MS.

Who can take natalizumab?

Natalizumab is recommended for the treatment of 'highly active' relapsing MS.

You can take natalizumab if:

  • you have relapsing MS and you've had a relapse in the past year and MRI scans show new signs (lesions) that your MS is active despite taking another DMT
  • you have relapsing MS and - whether or not you've taken another DMT - you've had at least two relapses in the last year and MRI scans show new signs (lesions) that your MS is active

How does natalizumab work?

Natalizumab is an ‘antibody’, like those found naturally in your immune system which fight off infections. By attaching itself to certain immune cells, natalizumab prevents these cells from leaving the blood stream and entering the brain and spinal cord where they can cause inflammation and damage.

Natalizumab is given through a drip (known as an infusion), which takes about an hour. You need to go to hospital once every four weeks for the infusion, but you don't need to stay overnight.

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How well does natalizumb work?

MS drugs can be put into three groups based on how well they control it. Natalizumab is in the 'highly effective' group (the best group). This is based on how much it reduces relapses and slows down the rate at which people's disability gets worse.

Relapses dropped by: 68%

This means that in trials, on average, people saw a 68% drop in the number of relapses they had (compared to people who didn't take this drug).

Disability getting worse was slowed down by: 42%

This means that in trials, on average, people saw a 42% drop in the risk of their disability getting worse (compared to people who didn't take this drug).

What are the side effects of natalizumab?

Like all medicines, natalizumab can have side effects, but not everybody gets them. Your MS nurse or neurologist can discuss these with you and suggest ways to treat or manage them.

Some of the more common side effects are joint pain, fever, tiredness, a runny or blocked nose, sore throat, feeling or being sick, headache or dizziness.


Being treated with natalizumab can increase your chances of developing a rare viral brain infection called PML (progressive multifocal leukoencephalopathy).

Although the risk is small in the first two years for people with the highest risk - at around 1 in 500 - the risk in some people can go up a lot as time goes on. By November 2015 nearly 600 people taking natalizumab had developed PML. This means of over 140,000 people across the world taking this drug, four in every thousand have got PML. It's important to be aware of PML as it can be fatal (about one in four of the people with PML died).

Everyone taking natalizumab will be monitored to check for the early signs of PML. Your health care team should also tell you what to look out for and what to do if you notice those signs.

There are some factors that are known to increase your risk of developing PML. Your neurologist should talk to you about those risk factors and how they affect you.

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Page last updated: 26 Nov 2015

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