Natalizumab (Tysabri)

Natalizumab is a disease modifying therapy (DMT) for highly active relapsing MS. Its brand name is Tysabri and you take it as an infusion or by injection administered by a nurse.

Read the latest information about DMTs and coronavirus COVID-19

Jump to:

Who can take natalizumab (Tysabri)?

In Scotland, Wales and Northern Ireland you can have natalizumab (its brand name is Tysabri) if:

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

In England you can have this drug if:

  • you have relapsing MS and you’ve had at least two relapses in the last year and MRI scans show new signs that your MS is active. This is happening whether or not you’ve been taking another DMT

Back to the top

How does natalizumab (Tysabri) work?

Your immune system makes special types of cells to kill viruses and bacteria. But in MS these cells are thought to target nerves in your brain and spinal cord by mistake. Natalizumab (Tysabri) sticks to these cells (called T cells). It stops them before they get into your brain and spinal cord, where they would attack the covering (called myelin) around the nerves there.

Natalizumab is given through a drip (known as an infusion). It takes about an hour, with another hour for you to be monitored.

You need to go to hospital, but you don't need to stay overnight. You usually have the drug every four weeks. If you have it by injection, you also need to go to a clinic or hospital where a nurse will administer it. The injection takes less time than an infusion.

Back to the top

How well does natalizumb (Tysabri) work?

MS drugs can be put into three groups based on how well they control it. The effectiveness of natalizumab (Tysabri) is classed as 'high', the best of the three groups. This is based on how much it reduces relapses and slows down how fast people's disability gets worse.

Relapses dropped by: 68%

This means that in a trial, on average, people saw a 68% drop in the number of relapses they had. This was compared to people who took a placebo, a dummy treatment with no drug in it.

Disability getting worse was slowed down by: 42%

This means that in a trial, on average, people saw a 42% drop in the risk of their disability getting worse. This was compared to people who took a placebo.

Back to the top

What are the side effects of natalizumab (Tysabri)?

Compared to other DMTs the risk of side effects, especially serious ones, is among the highest.

After an infusion you might get these for a while:

  • hives (itchy skin)
  • headache
  • shivers
  • stomach upset
  • joint pains
  • sore throat
  • feeling sick, tired or dizzy.


Being treated with natalizumab can increase your chances of developing a rare viral brain infection called progressive multifocal leukoencephalopathy (PML). Up to one in four who get PML can die.

The risk of getting PML is small. Four in every 1,000 people who take natalizumab get it. By September 2017 around 750 people with MS who'd taken natalizumab had got PML (out of around 175,000 people across the world taking this drug).

Having a virus called the JC virus makes your risk of getting PML higher. Only one in 10,000 people who don't have this virus get PML. If you do have it, one in 500 people are at the highest risk of getting PML in the first two years of being on natalizumab. After that the risk goes up a lot. If your risk of PML is high your MS specialist will change your treatment, perhaps switching you to another DMT.

If you take natalizumab you'll get blood tests that look for the virus that causes it. If you're at risk of PML you'll be checked for early signs of it. Your MS team will tell you what to look out for and what to do if you notice signs of PML.

Back to the top

Natalizumab (Tysabri) and pregnancy, breastfeeding and contraception


No studies have shown that natalizumab (Tysabri) harms unborn babies. The drug doesn’t have a licence to be used in pregnancy, but we know it doesn’t cross the placenta from mother to baby early in a pregnancy.

If you want to get pregnant, your neurologist may recommend that you keep taking natalizumab through your pregnancy. There’s a good reason to do this. If you stop, there’s a real chance that within 3 to 4 months your MS will get much worse. This is called ‘rebound’.

When you’re pregnant, you usually see your chances of a relapse drop. But this natural protection can’t be relied on if you’re on natalizumab. That’s because if you’re on this drug, it’s because you have a very active type of MS.

Some women agree to carry on having infusions until around week 34 of their pregnancy. They then start it again within 8 to 12 weeks of the baby’s birth to avoid rebound. Instead of infusions every four weeks, they might also get them every six or eight weeks during the pregnancy. The drug is likely to work just as well.

If you want to have a baby, you and your neurologist will weigh up the potential risk to the baby against the risk of stopping the drug (and of your MS getting worse). If you decide to stop taking it before getting pregnant, two months is this drug’s ‘washout period’. That’s how long it takes for amounts of it in your body to drop to a level where it’s safe to get pregnant.

If you and your partner want to have a child, discuss this with your neurologist. If you think you’ve become pregnant, let your medical team know at once. Never stop your DMT without first getting their advice.


UK experts think it’s unlikely a baby will take in any of the drug from breast milk.


There are no special recommendations about contraception for people being treated with natalizumab (Tysabri).

Back to the top