Leqembi (lecanemab-irmb) is a prescription drug that’s used to treat Alzheimer’s disease. Leqembi comes as a liquid solution that’s given as an intravenous (IV) infusion. A healthcare professional administers this drug.

Leqembi is prescribed to treat Alzheimer’s disease in adults who have mild cognitive impairment or mild dementia.

To learn more about Leqembi’s uses, see the “What is Leqembi used for?” section below.

Leqembi basics

Leqembi contains the active ingredient lecanemab-irmb.* (An active ingredient is what makes a drug work.) It belongs to a group of drugs called monoclonal antibodies.

Leqembi is a brand-name biologic drug. A biologic drug is made from living cells, while other drugs are made from chemicals.

Leqembi doesn’t come in a biosimilar form. Biosimilars are like generic drugs. But unlike generics, which are made for nonbiologic drugs, biosimilars are made for biologic drugs.

* The reason “-irmb” appears at the end of the drug’s name is to show that the drug is distinct from similar medications that may be created in the future.

Leqembi is used to treat Alzheimer’s disease in adults. The treatment is typically started when people are in the early stages of dementia.

Early stages include mild cognitive impairment and mild dementia. In these early stages, a person has a slight decline in their ability to remember things and think clearly. They may get confused or repeat themselves. But, in general, the person is still able to carry on with their usual daily activities.

Alzheimer’s disease occurs due to changes in the brain. One such change is the buildup of a protein called beta-amyloid. In studies, Leqembi was shown to remove the buildup of beta-amyloid in adults with mild Alzheimer’s disease. This may help delay or slow progression (worsening) of the disease.

Whether you have health insurance or not, cost may be a factor when you’re considering Leqembi. What you’ll pay for Leqembi may depend on several factors, such as your treatment plan, pharmacy, or healthcare professional.

If you have questions about how to pay for your prescription, talk with your doctor or pharmacist. A savings program called Eisai Patient Support may be available. You can also check out this article to learn more about saving money on prescriptions.

Like most drugs, Leqembi may cause mild or serious side effects. The lists below describe some of the more common side effects that Leqembi may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • your age
  • other health conditions you have
  • other medications you take

Your doctor or pharmacist can tell you more about the potential side effects of Leqembi. They can also suggest ways to help reduce side effects.

Mild side effects

Here’s a list of some of the mild side effects that Leqembi can cause. To learn about other mild side effects, talk with your doctor or pharmacist, or read Leqembi’s prescribing information.

Mild side effects of Leqembi that have been reported include:

  • infusion reactions that are mild, such as dizziness, rash, or nausea
  • headache
  • coughing
  • diarrhea
  • mild allergic reaction*

Mild side effects of many drugs may go away within a few days to a couple of weeks. But if they become bothersome, talk with your doctor or pharmacist.

* To learn more about this side effect, see the “Allergic reaction” section below.

Serious side effects

Serious side effects from Leqembi can occur, but they aren’t common. If you have serious side effects from Leqembi, call your doctor right away. But if you think you’re having a medical emergency, you should call 911 or your local emergency number.

Serious side effects of Leqembi that have been reported include:

  • infusion reactions that are severe, such as trouble breathing, fever, or changes in blood pressure
  • atrial fibrillation (an irregular heartbeat)
  • decreased level of infection-fighting white blood cells called lymphocytes
  • boxed warning: risk of amyloid-related imaging abnormalities*
  • severe allergic reaction†

* For more information, see the “What should be considered before taking Leqembi?” section below.
† To learn more about this side effect, see the “Allergic reaction” section below.

Allergic reaction

Some people may have an allergic reaction to Leqembi.

Symptoms of a mild allergic reaction can include:

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include swelling under your skin, usually in your eyelids, lips, hands, or feet. They can also include swelling of your tongue, mouth, or throat, which can cause trouble breathing.

Call your doctor right away if you have an allergic reaction to Leqembi. But if you think you’re having a medical emergency, call 911 or your local emergency number.

If you’d like to explore an alternative to Leqembi, talk with your doctor. They can tell you about other medications that might work well for you. Some other drugs that treat Alzheimer’s disease include:

  • aducanumab-avwa (Aduhelm), another monoclonal antibody similar to Leqembi
  • certain cholinesterase inhibitors, such as:
    • rivastigmine (Exelon)
  • memantine (Namenda), an NMDA receptor antagonist
  • donepezil/memantine (Namzaric), a combination drug

Find answers below to some commonly asked questions about Leqembi.

How does Leqembi work?

The buildup of a protein called beta-amyloid is one of the changes in the brain seen in people with Alzheimer’s disease. In studies, Leqembi was shown to reduce the buildup of beta-amyloid in adults with mild Alzheimer’s disease. Decreasing this buildup may delay or slow progression (worsening) of dementia.

Can Leqembi cure Alzheimer’s disease?

No, Leqembi doesn’t cure or reverse Alzheimer’s disease. Instead, it’s used to help delay or slow progression of the condition.

Talk with your doctor to learn more about what to expect from Leqembi treatment.

Does Leqembi cause long-term side effects?

It’s not known if Leqembi causes any long-term side effects.

Long-term side effects refer to side effects that either:

  • start during treatment and continue for a long time, possibly after treatment ends, or
  • start after you’ve taken the drug for a long time or after ending treatment

In studies of the drug, people received Leqembi treatment for up to 18 months. No long-term side effects were reported in these studies.

Leqembi was approved by the Food and Drug Administration (FDA) in 2023 and is still relatively new. Because of this, limited information is available about long-term side effects.

If you have questions about possible side effects with Leqembi, talk with your doctor.

Your doctor will recommend the dosage of Leqembi that’s right for you. Below are commonly prescribed dosages, but the dosage you receive will be determined by your doctor.

Form and strength

Leqembi comes as a liquid solution in single-dose vials. It’s available in one strength of 100 milligrams per milliliter (mg/mL). Leqembi vials come in two different sizes: 200 mg/2 mL and 500 mg/5 mL.

Recommended dosage

Your dosage of Leqembi depends on your body weight. The recommended dose is 10 milligrams (mg) of Leqembi for every kilogram (kg) of body weight. One kg is approximately 2.2 pounds (lb).

You’ll receive this dose once every 2 weeks.

How it’s given

You’ll receive Leqembi at your doctor’s office or another healthcare facility. A healthcare professional will prepare and administer the drug as an intravenous (IV) infusion (an injection into a vein given over time).

Before the infusion, you may be given certain medications to help prevent side effects called infusion reactions.

It takes about an hour to receive Leqembi. A healthcare professional will monitor you during and after the infusion.

Questions about taking Leqembi

Below are some common questions about taking Leqembi.

  • What if I miss a dose of Leqembi? If you miss an appointment to receive Leqembi, call your doctor’s office to reschedule. They’ll reschedule your appointment as soon as possible.
  • Will I need to use Leqembi long term? If you and your doctor decide that Leqembi is safe and effective for you, you’ll likely take it long term.

Below is important information you should consider before taking Leqembi.


Taking a drug with certain medications, vaccines, foods, and other things can affect how the drug works. These effects are called interactions.

Leqembi is not known to interact with other medications, herbs, supplements, foods, or alcohol. The drug’s manufacturer did not list any interactions in the drug’s prescribing information.

Before starting Leqembi treatment, talk with your doctor and pharmacist. Tell them about all prescription, over-the-counter, and other drugs you take. Also, tell them about any vitamins, herbs, and supplements you take. Sharing this information can help you avoid potential interactions.

If you have questions about drug interactions that may affect you, talk with your doctor or pharmacist.

Pregnancy and breastfeeding

It isn’t known whether Leqembi is safe to use during pregnancy or while breastfeeding. The drug hasn’t been studied in these situations.

If you’re pregnant or breastfeeding a child, or if you’re planning either, talk with your doctor. They’ll discuss your treatment options.

Boxed warning

Leqembi has a boxed warning. This is a serious warning from the Food and Drug Administration (FDA) about drug effects that may be dangerous.

Leqembi may cause amyloid-related imaging abnormalities (ARIA). ARIA are changes in the brain as seen on an MRI. These changes can include swelling or bleeding in the brain. ARIA doesn’t usually cause symptoms, but some people may experience:

  • confusion
  • dizziness
  • headache
  • nausea
  • seizures
  • vision changes

In rare cases, ARIA can be life threatening and lead to death.

Due to genetic differences, certain people may be at higher risk for ARIA than others. If you’ve inherited two copies of a gene called APOE-e4, you’re more likely to develop ARIA while taking Leqembi. This is compared to someone who has only one copy or no copies of this gene. To determine whether you have an increased risk of ARIA, your doctor may recommend genetic testing before starting treatment with Leqembi.

It isn’t known whether people with risk factors for bleeding in the brain are also at higher risk of developing ARIA from Leqembi. Examples of risk factors for bleeding in the brain include a prior hemorrhagic (bleeding) stroke or brain aneurysm (bulging blood vessel in the brain). Leqembi hasn’t been studied in these situations, so it isn’t known if these factors raise the risk of developing ARIA.

Before and during Leqembi treatment, your doctor will schedule head MRI scans to monitor you for ARIA. If you develop ARIA, your doctor may have you stop Leqembi treatment.

Talk with your doctor for more information about ARIA and Leqembi.

Other warnings

Leqembi can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Leqembi is the right treatment option for you.

Talk with your doctor about your health history before you take Leqembi. Be sure to tell them if any of the following factors apply to you:

If you have questions about taking Leqembi, talk with your doctor or pharmacist. Questions you may want to ask include:

  • What should I do if Leqembi doesn’t seem to be helping my condition?
  • How does Leqembi compare with other treatments for Alzheimer’s disease?
  • If I can’t afford Leqembi, what options do I have?
  • Are there any lifestyle changes that may help prevent my condition from worsening?

To get information on different conditions and tips for improving your health, subscribe to any of Healthline’s newsletters. You may also want to check out the online communities at Bezzy. It’s a place where people with certain conditions can find support and connect with others.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

Leqembi Images