Lecanemab
Dementia information
Lecanemab is a new medicine used to treat the very early stages of Alzheimer's disease.
You may have questions about this treatment and be looking for more information.
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Lecanemab is the first drug approved in the UK that can slow down Alzheimer's. Another drug, called donanemab, has also been licensed.
Lecanemab is not available on the NHS, or HSC in Northern Ireland.
It is currently only approved for use by specialist private healthcare providers in the UK.
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This information was updated in February 2025. It will be updated if, and when we learn of new developments.
This information has been written without input from pharmaceutical companies.
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What is lecanemab?
Lecanemab (lek-an-e-mab), also called LEQEMBI®, is a new drug treatment for Alzheimer’s disease and mild cognitive impairment (MCI). It is made by the drug company Eisai.
It has been licensed for prescription in the UK for people with a confirmed diagnosis of:
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Mild or early-stage Alzheimer’s disease.
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Mild cognitive impairment who have high levels of a protein called amyloid in their brain.
Lecanemab is not available on the NHS.
Lecanemab was the first drug licensed in the UK that targets one of the underlying disease processes that affects the brain in Alzheimer’s. A second drug, donanemab, has since also been licenced in the UK. Lecanemab and donanemab work in a similar way.
Lecanemab is designed to slow down Alzheimer's disease.
Existing treatments like donepezil, rivastigmine, galantamine and memantine can relieve some of the symptoms of Alzheimer’s but do not stop it from getting worse.
Lecanemab is not a cure but may allow some people with early Alzheimer’s to live independently and with milder symptoms for longer.
Lecanemab has not been approved to treat people with moderate to severe Alzheimer’s. There is currently no evidence that it can treat other types of dementia, such as vascular dementia, dementia with Lewy bodies or frontotemporal dementia.
Beyond lecanemab, there are over 100 other drugs for different types of dementia currently in clinical trials. At Alzheimer's Research UK, we believe it is a case of when, not if, a safe and effective treatment will become widely available for people living with dementia.
How does lecanemab work?
Lecanemab is a type of drug called a monoclonal antibody. This is where the "mab" in lecanemab comes from.
Antibodies are part of our immune system and bind to harmful proteins to destroy and remove them.
Lecanemab contains antibodies which bind to a protein called amyloid, which builds up in the brains of people with Alzheimer’s.
Although our bodies naturally produce antibodies, the specific anti-amyloid antibodies used in this treatment are created in a laboratory.
Other drugs for dementia, like donepezil, rivastigmine, galantamine and memantine, are known as ‘symptomatic’ treatments. These allow our brain cells to communicate better and mask the symptoms caused by diseases like Alzheimer’s for a time.
Although symptomatic treatments can make a big difference to somebody’s quality of life, they do not slow or stop Alzheimer’s from getting worse.
By directly targeting amyloid, lecanemab can slow down the disease process.
You may be prescribed a symptomatic treatment and lecanemab at the same time. There is no evidence that there any negative side effects when used in combination.
The graph below shows the effect on dementia symptoms over time.
How is lecanemab taken? How often will I have lecanemab?
Lecanemab is given via a drip into a vein in the arm. This is called an intravenous infusion. It involves a clinic visit while the medicine is given.
A doctor or nurse will deliver the treatment so they can check for any side effects. It’s likely that regular infusions will take around one hour, but your first few appointments may take a bit longer.
After your infusion, you will need to wait for at least half an hour before leaving the clinic. This is so staff can monitor you for side effects.
You need to have the medicine every two weeks.
At the moment it is not possible to have lecanemab from home. Lecanemab is not available as a tablet. Ongoing trials are looking into whether lecanemab can be injected under the skin.
Who can have lecanemab?
Lecanemab is only suitable for people with a diagnosis of:
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Mild or early-stage Alzheimer’s disease.
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Mild cognitive impairment who have high levels of a protein called amyloid in their brain.
Find out more about getting a dementia diagnosis here.
A diagnosis of Alzheimer's disease or mild cognitive impairment due to Alzheimer's disease requires testing for specific proteins found in the brain.
These proteins are called amyloid and tau.
When someone has a diagnosis of mild cognitive impairment with high levels of amyloid and tau in the brain, this is sometimes known as prodromal Alzheimer's disease.
At the moment in the UK, lecanemab is only available privately. Contact the Dementia Research Infoline for more information on 0300 111 5111 or infoline@alzheimersresearchuk.org
Amyloid tests
If you have either diagnosis listed above, you will need to have a type of brain scan called a PET scan or a spinal fluid test (lumbar puncture).
The clinic offering lecanemab will do this before you start the drug, to find out whether you have high levels of amyloid in your brain. This is the harmful protein that lecanemab clears.
Genetic tests
You will also have a genetic test to look for the APOE4 gene. This gene has been linked to a higher risk of lecanemab side effects, such as brain swelling and bleeds.
People with two copies of this gene (one from their mother and one from their father) are not eligible for lecanemab in the UK.
Brain scans
You will also need an MRI brain scan before you start treatment, and then at regular intervals while you are on treatment. These scans monitor for side effects of lecanemab.
What medications are unsafe with lecanemab?
People taking certain anticoagulants (blood thinners), may not be eligible for lecanemab. This is due to a higher risk of having brain swelling and brain bleeds.
How will lecanemab help me?
This new drug has been shown in clinical trials to slow down decline in memory and thinking problems for people with mild Alzheimer’s disease and improve quality of life.
Data from the trial shows that lecanemab can slow down memory and thinking getting worse on average by 27% among people taking the drug, compared to people on placebo (dummy drug).
There is no evidence that lecanemab can restore lost memories or make symptoms go away completely. The aim of treatment is that your symptoms decline less over time.
This could allow you to live independently for longer. Researchers estimate that over 18 months the drug may slow down disease progression by four to six months.
What are the side effects?
Infusion-related reactions
Some people taking lecanemab have reactions related to the drug being given into the vein. These are called ‘infusion-related reactions’ and can happen with many drugs given in this way, such as drugs given for cancer.
When something new is injected into your body, your immune system tries to fight it. Usually, this keeps us safe from harmful viruses and bacteria. But our immune system doesn’t know that lecanemab is actually trying to help us. This can produce symptoms such as fever, redness, and itchiness.
Your doctor may prescribe you medicines to help prevent this reaction, such as antihistamines or steroids.
Around one in four people taking lecanemab experienced infusion-related reactions in trials. Of these, three out of every four people did so only during their first appointment.
ARIA
Lecanemab can also cause brain swelling and bleeding. This is called “ARIA”, or amyloid-related imaging abnormalities.
While for the most part these are not associated with symptoms or adverse outcomes, they can in some cases be serious. Everyone on lecanemab will have regular MRI brain scans to monitor for signs of ARIA. People at higher risk of ARIA are also not eligible for lecanemab.
In trials of the drug, roughly one in eight people developed ARIA. However most (four in every five) of the people who developed ARIA did not have symptoms.
Symptoms of ARIA may include:
If you experience any of the symptoms above, you should call 999 or go to the nearest A&E as soon as possible.
It is important to get these symptoms checked quickly and to let any doctor you see know that you are taking this medication.
Out of 898 people who took lecanemab in the clinical trial, there were three deaths related to the drug. This is less than two in a thousand (0.02%) of the participants who took part in the trial.
Can I take other medications at the same time as lecanemab?
Anyone considering lecanemab must tell any doctor they see what other medications they are taking.
People with dementia may also be prescribed drugs to help with memory and thinking problems. These include donepezil, galantamine, rivastigmine and memantine. These are safe to continue alongside lecanemab.
There are some medicines, such as blood thinners (also known as anticoagulants), that can also increase risk of severe side effects. Some commonly prescribed blood thinners in the UK are warfarin, apixaban, dabigatran, edoxaban and rivaroxaban.
If you are taking one of these medications and lecanemab you must tell any doctor that you see about the medications you are prescribed because they may lead to more serious side effects.
You can find out whether any medication you may be taking is known to interact with lecanemab here. Because this is a new drug, scientists are still learning more about how it works. This means that there may be some drugs that increase the risk of lecanemab side effects that we don’t know about yet.
Lecanemab or donanemab?
In 2024, both lecanemab and donanemab were licensed for use in the UK. However, neither are available on the NHS. They both work in similar ways, but there are some practical differences.
Effectiveness
In clinical trials, lecanemab slowed Alzheimer’s by 27% whilst donanemab slowed Alzheimer’s by 35%. However, it’s important to note that the two studies were set up very differently. More trials are needed to directly compare the drugs and find out whether one is better at slowing the disease down.
Appointments
Lecanemab requires a one-hour infusion every two weeks. Donanemab requires a 30-minute infusion every four weeks.
Treatment course
People taking lecanemab will be on the drug indefinitely. People taking donanemab will be on the drug for 18 months, and will then stop.
Cost
The cost of each donanemab appointment is higher than lecanemab. However, as people stop taking donanemab after 18 months, the long-term costs may be lower.
It’s worth talking to your chosen healthcare provider about the differences in cost, as these will vary between providers.
What else should I know?
People who are allergic to any of the ingredients in lecanemab should avoid having the drug.
People with certain brain conditions (some strokes, or evidence for minor bleeding on the brain) may be at higher risk of side effects and in some cases may not be allowed to have the medicine.
This is one of the reasons that an MRI scan needs to be performed before treatment is considered. Your doctor will discuss the results of the scan with you to ensure you are eligible, and as part of the process of helping you decide whether you wish to take the medicine.
Anyone taking lecanemab will need a carer or loved one to come with them to appointments. If this is not possible, they should arrange an emergency contact.
Alzheimer’s Research UK have been providing lecanemab updates since the trial results were released in 2022. You can read our explainer for more information about its development.
Find out more
You can find out more about current diagnosis and treatments for each type of dementia on the following pages:
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This information is currently under review. It was written by Alzheimer's Research UK's Information Services team with input from lay and expert reviewers. Please get in touch if you'd like a referenced copy.
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