An oral MS disease-modifying medicine
Dimethyl fumarate
An oral medicine that reduces relapses in multiple sclerosis, with early flushing and stomach upset and a need for blood monitoring.
What is Dimethyl fumarate?
Dimethyl fumarate is a capsule taken by mouth to reduce relapses in people with relapsing multiple sclerosis. It calms the overactive immune attack on the nerves and is taken long term as a disease-modifying treatment rather than something used to settle a single relapse. In the early weeks it commonly causes flushing (a warm, red feeling in the face) and stomach upset, which usually settle and can be eased by taking it with food. It lowers a type of white blood cell called lymphocytes, so regular blood tests are needed; very rarely, a serious brain infection called PML has been linked to low white cell counts, which is why monitoring matters.
Education and reference only. This is a plain-language guide to Dimethyl fumarate — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Dimethyl fumarate is an oral disease-modifying therapy for relapsing multiple sclerosis, a condition in which the immune system mistakenly attacks the protective coating around nerves. It is taken as a capsule, usually twice a day, and is meant to be taken continuously over the long term to reduce how often relapses happen and to slow the build-up of disability. It is not a cure and does not reverse existing damage, but it helps keep the disease quieter. It is one of several oral options for MS and is generally considered a moderate-strength treatment.
How it works
Dimethyl fumarate is thought to dampen the inflammation that drives multiple sclerosis and to protect cells against the stress of that inflammation, partly by shifting the immune system into a less aggressive state. By doing so it reduces the number of relapses and the new areas of damage seen on scans. As part of this effect it lowers the number of lymphocytes, a type of white blood cell, which is why blood counts are watched closely. The benefit builds gradually over months rather than being felt straight away.
Company & origin
Originated / developed by: Biogen.
An oral disease-modifying treatment used in the UK for relapsing forms of multiple sclerosis.
Practical use
How to take Dimethyl fumarate
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take the capsules by mouth, usually twice a day, swallowing them whole without crushing or chewing.
- Taking each dose with food, especially something containing a little fat, often reduces flushing and stomach upset.
- Expect flushing and tummy symptoms to be most noticeable in the first weeks and to settle for most people; your team can suggest ways to ease them.
- Do not stop or skip doses on your own; speak to your MS team first, as keeping the disease controlled matters.
- Attend all your blood-test appointments, as these check your white cell counts and overall safety.
- Report any new weakness, clumsiness, vision changes, confusion or memory problems straight away.
Weighing it up
Advantages & disadvantages of Dimethyl fumarate
Advantages
- An oral capsule that reduces relapses without the need for injections or infusions.
- Early flushing and stomach effects usually settle, and can be eased by taking it with food.
- A well-established option with a long record of use in relapsing multiple sclerosis.
Disadvantages
- Commonly causes flushing and stomach upset in the early weeks, which some people find hard to tolerate.
- Lowers white blood cells and requires regular blood-test monitoring.
- Carries a rare risk of a serious brain infection (PML), especially if white cell counts stay low.
Practical use
Good to know
The two effects most people notice early are flushing and stomach upset, and these are the main reasons people consider stopping in the first weeks. Flushing feels like a hot, red, sometimes itchy sensation in the face and neck; taking the capsule with food, and sometimes a non-aspirin painkiller beforehand on advice, can help, and it usually fades as the body adjusts. The most important safety point is that the medicine lowers lymphocytes, and persistently low counts are linked to a rare but serious brain infection called progressive multifocal leukoencephalopathy (PML). Because of this, blood counts are checked before starting and regularly afterwards, and the medicine may be paused or stopped if counts fall too low. Tell your team promptly about any new weakness, clumsiness, vision changes, confusion or personality changes, as these can be warning signs.
Who should not take it / use with caution
- People with a serious active infection, or with persistently very low white cell counts, generally should not take it until reviewed.
- It is usually avoided in pregnancy and breastfeeding unless a specialist judges it necessary.
- People with significant liver or kidney problems need careful specialist assessment before use.
Monitoring
- Blood counts, including white cells, before starting and regularly during treatment.
- Liver and kidney function tests at intervals.
- Watching for warning signs of infection, including the rare brain infection PML.
Side effects
- Flushing (a warm, red feeling in the face) and stomach upset such as nausea, cramps or diarrhoea, mainly early on.
- A fall in white blood cells (lymphopenia), which is why blood tests are needed.
- Rarely, a serious brain infection (PML) linked to low white cell counts, or liver or kidney effects.
Key interactions
- Combining it with other medicines that suppress the immune system can increase the risk of infection and should be specialist-guided.
- Live vaccines are generally avoided while taking it, as the immune response may be affected.
- Other fumarate-containing products should not be taken alongside it to avoid doubling up.
Available as: Gastro-resistant capsules taken by mouth.
Answers
Dimethyl fumarate: frequently asked questions
Why do I feel hot and red after taking it?
Flushing is a very common early effect; it usually settles over time, and taking the capsule with food can help reduce it.
Why do I need regular blood tests?
The medicine lowers a type of white blood cell, and blood tests make sure your counts stay safe and help spot any rare problems early.
What is PML and how worried should I be?
PML is a rare but serious brain infection linked to low white cell counts; it is uncommon, which is why monitoring exists, and you should report new weakness, vision or thinking changes promptly.
Can I stop it if the stomach upset is bad?
Speak to your MS team first rather than stopping on your own; the early effects often settle, and they can suggest ways to make it easier.
Will it cure my multiple sclerosis?
No. It is a disease-modifying treatment that reduces relapses and slows damage over time, but it does not cure MS or reverse existing damage.
Authoritative sources
- BNF
- NICE CKS
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