Cladribine (Mavenclad)

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• Who can take cladribine (Mavenclad)?
• How do you take cladribine (Mavenclad)?
• How does cladribine (Mavenclad) work?
• How well does cladribine (Mavenclad) work?
• Cladribine (Mavenclad) side effects
• Stopping cladribine (Mavenclad)
• What tests do you need with cladribine (Mavenclad)?
• Cladribine (Mavenclad) and pregnancy, breastfeeding and contraception

In spring 2026 the makers of Mavenclad changed its name. They now call their drug ‘Cladribine Merck 10mg tablets’. It’s exactly the same product. In the coming months, you might get the drug with either name on the packaging.

Who can take cladribine (Mavenclad)?

In the UK, you can take cladribine (Mavenclad) if you have ‘active’ or ‘very active’ relapsing MS and your neurologist thinks a drug like cladribine is a suitable treatment for your type of MS. 

‘Active’ MS means you have relapses, or MRI scans show that you have new, active or growing lesions. Or another DMT hasn’t worked well enough (you've had a relapse in the last year and new, active or growing lesions on scans). 

‘Very active’ means you’ve had two or more relapses in the last year, with new, active or growing new lesions on scans.

You might not be able to take this drug if you have certain health issues, like liver or kidney problems, or cancer.

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How do you take cladribine (Mavenclad)?

You take cladribine (Mavenclad) for MS as tablets in two courses. And each treatment course consists of two treatment weeks. There's one at the beginning of the first month and one at the beginning of the second month. The number of tablets you take in each treatment week is worked out based on your weight.

This is then repeated a year later for your second treatment course. Hopefully the two courses will control your MS, and you won’t need any more treatment for several years or even longer.

Most people have treatment in year one and two, then no treatment in year three and four. 

Treatment schedule for cladribine (Mavenclad):

• Year one – month one – 4 or 5 days of treatment
• Year one – month two – 4 or 5 days of treatment
• Year two – month one – 4 or 5 days of treatment
• Year two – month two – 4 or 5 days of treatment
• Year three – no treatment
• Year four – no treatment

If you have relapses or MRI scans show you have new lesions, your doctor may suggest you take cladribine again in year 3 or 4. Or you could try another drug.

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How does cladribine (Mavenclad) work?

Cladribine (Mavenclad) works by targeting certain types of blood cells made by your immune system. These white blood cells (or lymphocytes) are called T and B cells.

These cells normally attack viruses and bacteria that get into your body. But in MS they attack the protective covering (called myelin) around nerves in your brain and spinal cord. Cladribine stops these cells from getting into your brain and spinal cord, so they can’t damage the nerves there. 

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How well does cladribine (Mavenclad) work?

The effectiveness of cladribine (Mavenclad) is classed as ‘good’. Each DMT can be rated as ‘moderate’, ‘good’ or ‘high’. This is based on how much it can reduce relapses and slow down disability getting worse. 

In a large trial called CLARITY, which reported its results in 2010:

Relapses dropped by 58% compared to placebo

During the two years of the CLARITY trial, on average, people who took cladribine had 58% fewer relapses than people who took the placebo. A placebo is a dummy treatment with no drug in it.

Disability getting worse was slowed by 33% compared to placebo

In the CLARITY trial, on average, people saw a drop of 33% in the risk of their disability getting worse (compared to people who took the dummy pill).

Over the two years the trial lasted, nearly half of people (46%) had no signs their MS was still active. That means they didn’t have relapses and on their MRI scans there were no new or active lesions.

The two-year CLARITY-Extension study reported its results in 2017. People who had taken cladribine for two years in the CLARITY study either took cladribine for another two years or a placebo. The two groups had similar results.

This means that after two years of treatment with cladribine, most people did not need more treatment in years three and four. 

Long-term results

If you have taken or are thinking about taking cladribine (Mavenclad), you might wonder what happens after four years.

Some people have not needed any further treatment, even after ten or more years. 

One study looked at long-term benefits in people who had taken cladribine as part of a clinical trial. They had taken cladribine an average of 10 years ago and some as long as 15 years ago. Over half had not needed treatment again. Their MS had not become active again (no relapses or new lesions on MRI scans). Taking cladribine meant they had a lower risk of needing to use a walking aid, wheelchair or giving up work than people who had not taken treatment.

But for some people, their MS becomes active again. Rates of relapse within five years of the last dose range from 30% to 50% in different studies.

Four years after finishing your cladribine treatment, you’ll decide with your neurologist what to do next. You may not need further treatment. But if your MS becomes active again, you and your neurologist can discuss your options. This might include taking cladribine again.

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Cladribine (Mavenclad) side effects

Cladribine (Mavenclad) is taken for a short time. This means your immune system is only weakened for a short time. Some other MS drugs affect the immune system for the whole time you are taking them. So, the risk of getting infections with cladribine isn’t as high as with some DMTs.

Very common side effects (more than 1 in 10 people get them):

• a drop in white blood cells (lymphopenia)

This is seen in about 1 in 4 to 1 in 3 people. Cladribine is meant to make this happen, but this drop can last a long time and be severe in some people.

Common side effects (up to 1 in 10 people get them):

• shingles
• cold sores
• rash
• a drop in other white blood cells (neutrophils)
• allergic reaction

The drop in white blood cells can cause other side effects. These include a slightly higher risk of getting headaches, colds, and infections caused by the herpes viruses. The skin rash shingles affects 1 in 50 people taking cladribine (Mavenclad). Cold sores are also common. Your doctor may recommend a vaccination to protect against shingles before you take cladribine.

Some people get some hair thinning on this drug.

If you ever need a blood transfusion or other blood products, these must be specially treated (irradiated) to prevent complications. It's important to tell your doctor that you have taken cladribine.

An earlier study seemed to show a higher risk of cancer, but we now know this isn't the case. 

A possible side effect of cladribine is liver damage (up to 1 in 100 people might get this). So blood tests will check your liver before you start cladribine (Mavenclad), and while the treatment lasts.

If you notice any signs of liver problems while you are taking cladribine, contact your doctor straight away. These include pain under your ribs on your right side, jaundice (yellowing of your skin or eyes), loss of appetite, feeling or being sick, dark pee and itchy skin.

Find out more about all the possible side effects of cladribine (Mavenclad)

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Stopping cladribine (Mavenclad)

You only need to take cladribine for a few days at a time. You don’t need to keep taking it after the course of treatment is finished. 

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What tests do you need with cladribine (Mavenclad)?

Tests before treatment begins

Before treatment starts, you'll have an MRI scan of your brain. This is so your doctor can compare this scan with later ones, to see how well the treatment is working.

You'll have a blood test to check your white blood cells before you start treatment for the first time, and before your second year of treatment. If your white blood cell count is low, treatment will be delayed.

You'll also have blood tests to rule out certain infections before you start treatment, like the liver disease hepatitis. 

A small number of people taking cladribine for MS developed serious liver problems. Some had existing liver problems. So you'll have tests to check your liver function before each course of treatment.

You'll be weighed, because the dose of cladribine is based on your body weight.

Vaccination 

Like most DMTs, this drug makes infections more likely. Before you start it, your neurologist will check if you have protection against some of the infections it puts you at risk of. 

Your neurologist will check you’re up to date on your vaccines. This includes childhood ones like chickenpox (that vaccine protects you against shingles) and the MMR vaccine for measles, mumps and rubella. Some ‘live’ vaccines, like these two, aren’t safe to have once you’ve started many DMTs. Your MS team or GP can tell you whether a vaccine is ‘live’ or not. 

You’ll have any vaccines you need a few weeks before you start this drug. 

You can safely have the annual flu jab while taking this DMT. 

Read more about vaccines 

Tests during treatment 

You'll have blood tests to check your white blood cell count two to three months and six to seven months after you take cladribine. You'll also have blood tests to check your liver function.

Your neurologist might want you to have an MRI scan once a year to see if the drug is working. But how often you have scans depends on what your neurologist thinks you need. If your MS seems stable, you might have scans less often.

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Cladribine (Mavenclad) and pregnancy, breastfeeding and contraception

Pregnancy

Cladribine (Mavenclad) could harm an unborn baby. So you mustn’t get pregnant while being treated with cladribine, or for six months after your final course of tablets. 

Six months is cladribine’s ‘washout period’. That’s how long it takes for it to leave your body.

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

Breastfeeding

It’s not clear if cladribine (Mavenclad) gets into breast milk. So women must not breastfeed while being treated with cladribine or for a week after their last dose.

Contraception

If you can get pregnant, you’ll need to use reliable contraception like ‘the pill’, condoms, a coil, injections or implant. You should use contraception while you are taking cladribine (Mavenclad), and for six months after your final course of tablets. 

There’s no evidence that taking cladribine has any effect on hormonal contraception. But the Association of British Neurologists recommend that if you’re using hormonal contraception (the pill, injections, patches or implants), you also use a barrier method of contraception. Barrier methods include a cap, diaphragm or condoms. You should do this for four weeks after finishing each course of tablets to be extra safe.

Cladribine (Mavenclad) can affect the quality of sperm for up to six months after your last course of tablets. This drug can also damage sperm, putting at risk any baby that’s conceived. Men should use reliable contraception while taking cladribine and for six months after finishing it. Your neurologist can give you more advice about fertility and contraception.

Read more about pregnancy, breastfeeding and contraception and DMTs

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