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By Mayo Clinic Staff

Lecanemab (Leqembi) is a medicine given to slow the progression of mild Alzheimer's disease (AD). This medicine reduces clumps of proteins in the brain called amyloid-beta that play a key role in the condition. Reducing this protein modestly slows the loss of memory and thinking, also known as cognitive decline.

Lecanemab is for people who have early AD with mild symptoms of memory and thinking loss. A recent trial of the medicine showed that taking lecanemab over 18 months slowed the rate cognitive decline. More research is needed to know if the medicine can help slow the progress of AD in people without symptoms of memory loss.

Lecanemab belongs to a newer group of Alzheimer's treatments called anti-amyloid monoclonal antibodies. A medicine called donanemab (Kisnula) also belongs to this group. Both medicines are used in early stages of AD and help remove amyloid-beta proteins from the brain.

Lecanemab is given as an IV infusion every two weeks. Your care team watches for side effects and asks you or your caregiver how your body reacts to the medicine.

Because lecanemab is a newer medicine, there is still much to learn about it. Some people who take lecanemab have side effects, and some of those side effects are serious.

Common side effects often happen because of a reaction to the IV infusion. These include:

• Dizziness.
• Headache.
• Visual changes.
• Fever.
• Nausea.
• Changes in blood pressure.
• Confusion that gets worse.

Serious side effects include:

• Swelling and bleeding in the brain. When these changes are seen in MRI scans, they are known as amyloid-related imaging abnormalities (ARIA). Studies show that ARIA happens in about 20% of the people who take lecanemab. But often it is mild and causes no symptoms. It's rare for ARIA to cause symptoms. This happens about 3% of the time. Less than 1% have severe symptoms.
• Death. Very rarely, severe ARIA in people who take lecanemab may lead to death.

If your side effects are severe, you may need care in a hospital. You also may have to stop taking the medicine.