Lecanemab (Leqembi)

What it treats

Lecanemab is approved by the U.S. Food and Drug Administration for early Alzheimer's disease, meaning mild cognitive impairment due to Alzheimer's or mild Alzheimer's dementia. Confirmation of brain amyloid is required before treatment starts, either by amyloid PET scan or by cerebrospinal fluid biomarkers.

It's not approved and not appropriate for moderate or severe Alzheimer's dementia, non-Alzheimer's dementias, or people without confirmed amyloid pathology. It also isn't a prevention drug for people who don't yet have symptoms.

How it works

Alzheimer's disease is associated with buildup of amyloid-beta protein in the brain. Not all forms of amyloid are equal. Soluble intermediate forms called protofibrils appear to be particularly toxic to neurons.

Lecanemab is an antibody engineered to bind these protofibrils and, to a lesser extent, insoluble plaque. Once bound, the brain's cleanup cells (microglia) can more effectively remove them. Over months of dosing, amyloid PET scans typically show substantial clearance.

The key honest framing: clearing amyloid doesn't reverse the disease. Downstream damage from tau tangles, inflammation, and neuronal loss continues. What the trial showed is a slower slope of decline, not a return of function.

Receptor mechanism (detail)

Lecanemab is a humanized IgG1 monoclonal antibody that binds selectively to soluble amyloid-beta protofibrils with high affinity, with lower affinity for fibrillar plaque and minimal binding to monomeric amyloid-beta. Antibody-bound amyloid is cleared by microglial phagocytosis and by transport out of the brain.

Potency and typical dosing pattern

Ranges are typical framework only, not a prescription for any individual.

Standard dosing is 10 mg per kilogram given intravenously every 2 weeks. Each infusion runs about an hour, and the person is usually monitored for a period afterward, especially in the early doses. There is no oral form.

Treatment is typically continued long term, though whether and when to stop after a defined period is an area of ongoing clinical judgment. Some clinicians consider a stop once amyloid PET has cleared; the label doesn't require it.

Safety monitoring

• Baseline brain MRI before treatment starts, with attention to microhemorrhages, superficial siderosis, and vascular changes. Certain findings on the baseline scan disqualify a person from starting.
• Follow-up MRIs before doses 5, 7, and 14, and any time new neurologic symptoms develop. The purpose is to catch ARIA.
• ApoE genotype testing before starting. ApoE4 homozygotes have the highest ARIA risk, and treatment in that group requires a careful conversation about risk versus benefit.
• Infusion reactions. Watch during and after each infusion, especially the first few.
• Anticoagulation status. People on warfarin, DOACs, or antiplatelet drugs face higher hemorrhage risk if ARIA develops. Coordinate with the prescribing team.
• New neurologic symptoms at any point (headache, confusion, visual changes, seizure, weakness) need urgent MRI evaluation.

What to expect

The 18-month trial framing is honest and important. Over that period, people on lecanemab declined more slowly on a global dementia score than people on placebo, by roughly 27 percent. In practical terms this is a small absolute effect that may translate to more months of independent function at the current stage. It doesn't roll back where the person already is.

The treatment experience itself is different from an oral pill. Every two weeks, the patient (usually with a care partner) comes to an infusion center for an intravenous infusion. Baseline and periodic MRIs are part of the schedule. Infusion reactions (chills, fever, flushing, back pain, mild rash) happen in a meaningful minority, especially at the first infusion.

ARIA is the safety story that stands apart. Some people develop swelling (ARIA-E) or small bleeds (ARIA-H) in the brain that show up on MRI. Most cases are asymptomatic and picked up on routine imaging, and most resolve with a pause in dosing. A minority are symptomatic and can be serious.

Common side effects

The most common issues in the CLARITY-AD trial and in practice:

• Infusion-related reactions (chills, fever, flushing, back pain, headache, mild rash).
• Headache.
• ARIA-E and ARIA-H on imaging, often asymptomatic.
• Fatigue.
• Falls.

Premedication with acetaminophen or diphenhydramine and slower infusion rates reduce infusion reactions.

Serious side effects and warnings

• ARIA (amyloid-related imaging abnormalities). This is the safety issue that defines this class of drugs. ARIA-E is brain swelling; ARIA-H is small hemorrhages or superficial siderosis. Most cases are asymptomatic and resolve with dose pause. A minority cause headache, confusion, visual changes, seizure, or focal neurologic symptoms, and rare cases have been fatal, particularly in people on anticoagulation or with widespread cerebral amyloid angiopathy. Any new neurologic symptom on lecanemab needs urgent MRI evaluation.

Other serious issues:

• Severe infusion reactions. Rare but reported, including anaphylaxis.
• Intracerebral hemorrhage. Higher risk in people on anticoagulation or with cerebral amyloid angiopathy.
• ApoE4 homozygote risk. ARIA rates are meaningfully higher in this group. The prescribing information recommends genotype testing and careful counseling before treatment.

Sexual and relational effects

Sexual side effects with lecanemab aren't a common complaint. The bigger relational dimension is the infusion schedule itself. Every-two-week infusions and multiple MRIs are a real burden for care partners, especially in the early months. Families should have a clear-eyed conversation about the modest expected benefit, the ARIA risk, the schedule, and the cost before starting.

Weight, appetite, and sleep

Lecanemab doesn't have a notable effect on weight, appetite, or sleep in trials or practice. The dominant lifestyle impact is the infusion schedule, not metabolic or sleep effects.

Starting and dosing basics

This section is general background, not a dosing instruction for any individual. The right dose is a decision for a prescriber.

Before starting: confirm amyloid pathology (PET or CSF), obtain baseline MRI, obtain ApoE genotype, review anticoagulation status, review the risk of ARIA with the patient and care partner. Some prescribers avoid or defer treatment in ApoE4 homozygotes given the elevated ARIA risk.

Treatment: 10 mg per kilogram intravenous every 2 weeks, infused over roughly an hour. Follow-up MRIs before doses 5, 7, and 14. Additional MRIs if new neurologic symptoms appear.

Missed doses and interactions

Missed infusions are rescheduled as soon as possible. There isn't a "loading" or restart protocol required after a modest gap.

Interactions to know:

• Anticoagulants (warfarin, DOACs) and antiplatelet agents beyond aspirin meaningfully raise hemorrhage risk if ARIA develops. Some experts avoid initiating anticoagulation during lecanemab treatment and are cautious about starting lecanemab in people already anticoagulated.
• Thrombolytics (tPA) in the setting of acute stroke carry a possibly higher hemorrhage risk in patients on anti-amyloid antibodies.
• Live vaccines don't have a specific contraindication but general immunization planning should be coordinated with the prescriber.

Stopping and tapering

Lecanemab doesn't require a taper. It can be stopped at any point. Reasons to stop include serious ARIA, poor tolerability, progression to moderate or severe dementia (where continued treatment no longer makes sense), or a shared decision that the burden of infusions and MRIs isn't worth the modest slowing of decline.

Whether and when to stop after a defined period, even in a person doing well, is an unsettled question. Some clinicians consider stopping once amyloid PET has cleared. Others continue.

Pregnancy and breastfeeding

This isn't a routine issue given the patient population. Lecanemab isn't studied in pregnancy or breastfeeding. Anyone in an unusual clinical situation involving reproductive planning should discuss it with a specialist.

Cost and generic availability

Lecanemab is brand-only and expensive. The wholesale price is roughly 26,500 dollars per year in the United States, and total costs (infusion, MRI monitoring, biomarker testing) are considerably higher than the drug alone. Medicare has covered lecanemab under specific conditions since 2023, typically requiring participation in a registry. Coverage details vary by plan.

Common questions

Will lecanemab bring my parent back? No. It slows the slope of decline. It does not restore what's already gone. This is important to say plainly before the decision to start.

Who is it for? People with early Alzheimer's (mild cognitive impairment due to Alzheimer's or mild Alzheimer's dementia) and confirmed brain amyloid. It's not for moderate or severe dementia, not for non-Alzheimer's dementia, and not for people without confirmed amyloid.

What is ARIA? Amyloid-related imaging abnormalities: brain swelling or small bleeds seen on MRI. Most cases are asymptomatic and picked up on routine monitoring. A minority cause headache, confusion, visual changes, or seizure. The risk is why regular MRIs are part of the treatment plan.

Why does ApoE4 matter? People with two copies of the ApoE4 gene have a substantially higher rate of ARIA. Some prescribers won't treat this group at all with lecanemab; others do only after a careful discussion of the added risk.

Is it worth 26,500 dollars a year? That's the honest question every family should ask. The trial benefit is real but small in absolute terms. The infusion schedule, MRIs, and ARIA risk are real. This is a decision that belongs with the family, the patient, and the prescriber together, not something anyone should feel rushed into.

Questions to ask your prescriber

• Is the diagnosis right, and has amyloid been confirmed?
• What does my ApoE genotype say about ARIA risk?
• What are we hoping to see over the next 18 months?
• What's the MRI schedule, and what happens if ARIA shows up?
• If I'm on a blood thinner, does that change the plan?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes, and current as of June 8, 2026.

• U.S. Food and Drug Administration. Lecanemab (Leqembi) prescribing information.
• DailyMed, U.S. National Library of Medicine. Lecanemab label.
• MedlinePlus, U.S. National Library of Medicine. Lecanemab.
• National Institute of Mental Health. Mental health medications.
• van Dyck CH, et al. Lecanemab in Early Alzheimer's Disease (CLARITY-AD trial). New England Journal of Medicine, 2023.
• American Academy of Neurology and American Psychiatric Association. Guidance on use of anti-amyloid monoclonal antibodies in Alzheimer's disease.
• Centers for Medicare and Medicaid Services. Coverage determination for anti-amyloid antibodies.