Leqembi (lecanemab-irmb) is a prescription drug that’s used to treat Alzheimer’s disease. The drug comes as a liquid that’s given as an infusion into a vein. It’s usually given once every 2 weeks.

Leqembi is prescribed to treat Alzheimer’s disease in adults with:

The active ingredient in Leqembi is lecanemab-irmb.* (An active ingredient is what makes a drug work.)

Leqembi belongs to a group of drugs called monoclonal antibodies. This article describes the dosage of Leqembi, its strength, and how it’s given. To learn more about Leqembi, see this in-depth article.

* 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.

The table below highlights the basics of Leqembi’s dosage. Drug strength is listed in milligrams per milliliter (mg/mL). Dosage is listed in mg of drug per kilogram of body weight (mg/kg).*

StrengthUsual recommended dosage
100 mg/mL10 mg/kg once every 2 weeks

Keep reading for more details about Leqembi’s dosage.

* For reference, 1 kg is about 2.2 pounds (lb).

What is Leqembi’s form?

Leqembi is available as a liquid solution in a vial. A healthcare professional will administer the drug as an intravenous (IV) infusion (an injection into your vein given over time).

What strength does Leqembi come in?

Leqembi comes in a strength of 100 mg/mL. Your doctor may order it in a 2-mL or 5-mL vial.

What is the usual dosage of Leqembi?

The information below describes the dosage that is commonly prescribed or recommended. But your doctor will determine the best dosage to fit your needs.

Dosage for Alzheimer’s disease

The usual Leqembi dosage for adults with Alzheimer’s disease depends on body weight. The recommended dose is 10 mg/kg. Your doctor will calculate and prescribe the correct dose for you. You’ll receive this dose as an IV infusion once every 2 weeks.

Is Leqembi prescribed long term?

Yes, Leqembi is usually prescribed as a long-term treatment. If you and your doctor determine that it’s safe and effective for your condition, you’ll likely receive it long term.

Dosage adjustments

Your doctor may adjust your dosing frequency of Leqembi based on side effects you experience, including the presence of amyloid-related imaging abnormalities (ARIA) on a brain scan.

Depending on the severity of the side effects, your doctor may choose to temporarily stop treatment with Leqembi until the side effect resolves. Afterward, your doctor may decide to resume your treatment with Leqembi, or they may recommend a different treatment they think would be safer.

The dosage of Leqembi you’re prescribed may depend on several factors. These include:

  • your body weight
  • whether you experience any side effects (see the “Dosage adjustments” section above)

You’ll receive Leqembi at your doctor’s office or at a clinic.

Leqembi comes as a liquid solution in a vial. The small volume of liquid in the vial is first diluted in a larger volume of liquid saline solution by a healthcare professional. You’ll then receive the medication as an intravenous (IV) infusion over about 1 hour. (An IV infusion is an injection into your vein given over time.)

Some people may experience an infusion-related reaction at the time of the infusion. Symptoms may include fever, chills, and nausea. A reaction can also cause changes in blood oxygen level and blood pressure. If this occurs, your doctor will stop the infusion and provide treatment for the reaction. The infusion can usually be started again but at a slower rate.

If you’ve had this experience, your doctor will likely give you medication to help prevent this reaction before your next infusion. Medications they may recommend to help prevent an infusion-related reaction include:

If you miss an appointment to receive a dose of Leqembi, call your doctor’s office as soon as possible to reschedule.

If you need help remembering your appointments, consider setting an alert on your calendar app or reminder app on your phone.

Below are answers to some commonly asked questions about Leqembi’s dosage.

Is Leqembi’s dosage similar to the dosages of Aricept?

Leqembi and Aricept (donepezil) are both prescribed to treat Alzheimer’s disease. But their forms, dosing schedules, and the way the drugs work in the body are different.

Leqembi comes as a liquid solution that’s given as an intravenous (IV) infusion (injection into a vein given over time) by a healthcare professional. It’s given once every 2 weeks. Dosage is based on body weight.

Aricept is available as a brand-name drug and as the generic drug donepezil. Aricept is available as a pill that is swallowed. The generic donepezil is available as a tablet that can be swallowed and as a tablet that is dissolved on the tongue. Either form is usually taken once per day and the dosage is not based on body weight.

Your doctor will prescribe the drug and the dosage that’s right for you. To learn more about how these drugs compare, talk with your doctor.

How long does it take for Leqembi to start working?

Leqembi starts to work after your first dose. Because of how the drug works, you likely won’t feel the drug working in your body.

The exact cause of Alzheimer’s disease isn’t known, but buildup of a substance called beta-amyloid is thought to play an important role. Leqembi works to reduce the amount of beta-amyloid plaques (buildup) in the brain. In studies, fewer beta-amyloid plaques were seen on PET scan imaging after 13 weeks of Leqembi treatment.

Your doctor will monitor how your condition responds to treatment with Leqembi. If you have questions about what to expect from your treatment, talk with your doctor.

The sections above describe the usual dosage provided by the manufacturer. If your doctor recommends Leqembi for you, they’ll prescribe the dosage that’s right for you.

Talk with your doctor if you have questions or concerns about your current dosage.

Here are some examples of questions you may want to ask your doctor:

  • How will you adjust my dosage of Leqembi if I experience side effects?
  • What medications can I try if I start to feel unwell during my Leqembi infusions?
  • If we decide Leqembi is not right for me, can I simply stop treatment or does the dosage need to be tapered?

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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.