The Food and Drug Administration on Thursday granted traditional approval to Leqembi, the first anti-amyloid Alzheimer’s treatment to move from the accelerated pathway to full approval after a confirmatory trial showed a 27% slowing of cognitive and functional decline over 18 months compared with placebo. The decision also opens broader Medicare coverage for eligible patients, turning a closely watched scientific result into a treatment that can reach substantially more people with early-stage disease.

FDA’s July 6 announcement said the agency determined that the confirmatory study verified clinical benefit. Leqembi, or lecanemab-irmb, is an antibody directed at amyloid beta, a protein that accumulates in plaques in the brains of people with Alzheimer’s disease. Treatment is intended for patients with mild cognitive impairment or mild dementia due to Alzheimer’s disease and confirmed amyloid pathology — the population studied in the clinical trials.

A confirmatory trial moves amyloid reduction into clinical benefit

Leqembi received accelerated approval in January based on evidence that it reduced amyloid plaques, a surrogate endpoint FDA considered reasonably likely to predict clinical benefit. Accelerated approval allowed the drug onto the market while requiring the manufacturers to verify whether that biological effect translated into a meaningful difference in how quickly patients’ memory, thinking and daily function deteriorated.

The answer came from the Phase 3 Clarity AD trial, published in the New England Journal of Medicine. The randomized, double-blind study enrolled 1,795 participants with early Alzheimer’s disease and confirmed amyloid pathology. Patients received intravenous lecanemab at 10 milligrams per kilogram every two weeks or placebo for 18 months. On the primary Clinical Dementia Rating–Sum of Boxes scale, decline was 27% slower in the treatment group than in the placebo group.

The percentage needs context. Leqembi does not restore lost memory or stop Alzheimer’s disease. Both groups worsened during the trial; the treatment group deteriorated more slowly on average. The absolute difference on the CDR-SB scale was modest, but FDA concluded that the result was statistically significant and clinically meaningful, with secondary measures of cognition and activities of daily living pointing in the same direction.

FDA’s Drug Trials Snapshot describes the confirmatory population and treatment schedule, noting that the study was conducted at 253 sites in 13 countries and that participants received infusions every two weeks. The agency has emphasized that safety and effectiveness have not been established for starting treatment in substantially earlier or later stages of Alzheimer’s disease than those studied.

The approval comes with a prominent brain-swelling and bleeding warning

The same biological mechanism that makes anti-amyloid antibodies potentially useful also creates an important safety problem. Leqembi can cause amyloid-related imaging abnormalities, or ARIA, which appear on MRI as swelling or small areas of bleeding in or around the brain. Many cases are asymptomatic and resolve, but some produce headache, confusion, dizziness, visual changes or nausea, and serious or life-threatening events can occur.

The traditional approval includes a boxed warning about ARIA. FDA said people who are homozygous for the ApoE ε4 allele have a higher incidence of ARIA, including symptomatic and severe cases, than heterozygotes and noncarriers. The prescribing information says ApoE ε4 testing should be performed before treatment to inform patients about risk. The agency also urges caution in patients taking anticoagulants because intracerebral hemorrhage occurred more often in treated patients receiving such drugs than in placebo patients.

These safety questions were central to the June 9 meeting of FDA’s Peripheral and Central Nervous System Drugs Advisory Committee. The agency’s meeting record contains the briefing materials used to evaluate whether Clarity AD verified clinical benefit. All committee members ultimately voted that the confirmatory evidence did so, clearing a major advisory hurdle before Thursday’s action.

Medicare coverage expands — with a registry requirement

For many patients, FDA approval is only half of the access question because most people with Alzheimer’s disease are Medicare beneficiaries. CMS had previously limited coverage of anti-amyloid monoclonal antibodies granted accelerated approval to qualifying clinical studies. Traditional FDA approval changes that position for Leqembi.

CMS said Thursday that broader Medicare coverage is now available. To qualify, a beneficiary must be enrolled in Medicare, have mild cognitive impairment or mild Alzheimer’s dementia with documented beta-amyloid plaque, and be treated by a physician participating in a qualifying registry with an appropriate clinical team and follow-up care.

The registry requirement is part of Medicare’s coverage-with-evidence-development approach for this class of drugs. Clinicians submit a limited set of data so researchers can study how the therapy performs in routine practice and answer questions identified in the national coverage determination. CMS says its facilitated registry is available now and that other qualifying registries may become available.

Patients with Original Medicare generally face the standard 20% Part B coinsurance after meeting the deductible, although supplemental insurance or Medicare Advantage can change individual costs. That makes the drug’s price and the expense of repeated infusions, imaging and specialist care part of the access debate even after coverage expands.

Manufacturers move from accelerated approval to commercial scale

Eisai and Biogen, which jointly developed and commercialize the drug, said the traditional approval validates the full Clarity AD data and permits broader access. Their July 6 announcement emphasized that Leqembi is the first approved therapy shown to slow the rate of cognitive and functional decline by targeting an underlying feature of Alzheimer’s disease rather than only treating symptoms.

That distinction is scientifically important but should not be overstated clinically. The treatment effect represents slower progression, not reversal. Patients and families will have to weigh the possibility of preserving function for longer against infusion burden, MRI monitoring, ARIA risk and out-of-pocket costs. The decision is likely to be especially complex for people carrying two ApoE ε4 alleles or taking anticoagulants.

Traditional approval also changes the evidence standard attached to the drug. Accelerated approval rested primarily on amyloid-plaque reduction as a surrogate marker. Full approval rests on the confirmatory clinical trial showing that patients declined more slowly on measures of cognition and function. That is the core regulatory transition FDA made Thursday.

A consequential but measured step in Alzheimer’s treatment

The field has spent decades pursuing therapies capable of modifying Alzheimer’s disease rather than simply treating symptoms. Leqembi provides evidence that reducing amyloid can alter the rate of decline in patients at an early stage, but it also illustrates why that achievement does not amount to a cure. The effect is partial, treatment is intensive, and safety monitoring is essential.

The FDA’s own framing is careful. The agency calls Thursday’s action the first verification that a drug targeting an underlying disease process in Alzheimer’s has demonstrated clinical benefit, while limiting use to the stage of disease studied. That balance reflects both the importance of the trial and the remaining uncertainty about how the results will translate across a much larger and more diverse real-world population.

Coverage will make that next phase possible. With Medicare now offering broader payment under a registry framework, clinicians will begin treating more eligible patients outside tightly controlled trials. The resulting data can help clarify how often serious ARIA occurs in practice, which patients benefit most, how long treatment should continue and whether the modest average slowing seen in Clarity AD is meaningful to individual patients and families.

As of Saturday, the milestone is therefore both scientific and practical: FDA has converted Leqembi to traditional approval on the strength of a 1,795-patient confirmatory trial, and Medicare has simultaneously opened a broader route to coverage. The therapy does not stop Alzheimer’s disease, but for the first time a fully approved treatment aimed at amyloid has shown that it can slow the clinical progression of early disease — while requiring patients and physicians to manage risks that are equally real.