Beta interferons

Beta interferons are disease modifying therapies (DMTs) for relapsing MS and in some cases secondary progressive MS. Their brand names are Avonex, Plegridy and Rebif and they are all taken as injections. Doctors in the UK no longer prescribe two other brands, Extavia and Betaferon. This isn't because of any safety issues, but because their makers took them off the market.

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Who can take beta interferons?

Beta interferons are recommended for the treatment of 'active' relapsing MS. This has been defined in guidelines as when you have two or more relapses in the last two years. But more and more MS specialists are defining 'active' MS as one recent relapse and/or signs on MRI scans that MS is active.

You can take beta interferons if:

  • you have relapsing MS and you've had a recent relapse and/or if MRI scans show new signs that your MS is active (you have new lesions)
  • you have a 'clinically isolated syndrome' or CIS (a first attack of MS-like symptoms) and a brain scan shows you're likely to go on to get MS

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How do beta interferons work?

Your body makes its own interferons (a protein) to dampen down inflammation. These drugs are manmade versions. They can reduce (and might prevent) the inflammation that damages nerves in MS.

Beta interferons are all injected, many with a 'pen' that means you don't see the needle going into your skin.

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How well do beta interferons work?

MS drugs can be put into three groups based on how well they control it. The effectiveness of beta interferons is classed as 'moderate'. This is based on how much they reduce relapses and slow down how fast people's disability gets worse.

Relapses dropped by: 33%

This means that in trials, on average, people saw a 33% 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:

a modest amount

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

Long-term evidence from people on beta interferons for years shows their effect is much bigger than 'modest' if you start one early on in your MS.

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What are the side effects of beta interferons?

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

After a beta interferon injection at least one in 10 people find they feel like they have flu, with headaches, muscle aches, chills or a fever. These usually last for no more than two days (48 hours) after the injection and often get better the longer you use the drugs. Ibuprofen or paracetamol can help, as can injecting before going to bed.

Your skin can become red, hard, bruised or itchy where you inject. Beta interferons might cause depression, so you might not be given one if you've had depression in the past.

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Beta interferons and pregnancy, breastfeeding and contraception


Guidelines say you can take beta interferons (Rebif, Plegridy and Avonex) while you're pregnant if your neurologist thinks you need to.

You might decide to stop taking your interferon a month before you try to get pregnant. One month (or less) is the ‘washout period’ for beta interferons. That’s how long it takes for levels of a DMT in your body to reach a level where it’s safe to get pregnant. But your neurologist may say there's no need for for this with beta interferons.

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.


Guidelines say you can breastfeed while taking a beta interferon. Women with MS are encouraged to breastfeed, including when on a beta interferon. The benefits of breastfeeding for the baby while its mother is on these drugs are bigger than any risk.


There are no special recommendations about using contraception while on a beta interferon.

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