The Food and Drug Administration this week approved Aduhelm, the first new treatment for Alzheimer’s disease since 2003 and the first approved therapy aimed at reducing one of the disease’s underlying pathological features, while taking the unusual step of relying on a surrogate biological endpoint after clinical trials produced conflicting evidence about whether the drug slows cognitive decline.

FDA granted the Biogen treatment, also known as aducanumab, accelerated approval on Monday. Under that pathway, the agency can authorize a treatment for a serious disease based on an effect that is reasonably likely to predict clinical benefit. In this case, FDA relied on the drug’s ability to reduce amyloid beta plaques in the brain and required Biogen to conduct a new randomized controlled trial to determine whether that biological change translates into meaningful benefit for patients.

The decision immediately divided the Alzheimer’s community. Patient advocates celebrated the arrival of a disease-targeting therapy after nearly two decades without a new approval. Other researchers and health-policy experts argued that the evidence does not yet establish that removing amyloid slows the memory loss, functional decline and cognitive deterioration that matter to patients.

FDA chose a surrogate endpoint after trials gave different answers

Aduhelm is a monoclonal antibody designed to bind aggregated forms of amyloid beta and reduce plaque in the brain. Biogen’s approval announcement said clinical trials showed reductions in amyloid plaques ranging from 59% to 71% at 18 months, depending on the study and dose.

The central controversy is that amyloid reduction is not the same thing as demonstrated clinical improvement. Biogen conducted two large Phase 3 studies that were stopped early after a futility analysis suggested they were unlikely to succeed. Subsequent analyses produced different conclusions: one trial showed a statistically significant slowing on its primary clinical measure at the high dose, while the other did not.

FDA’s summary review describes those conflicting results and the agency’s decision to use the accelerated pathway based on the total evidence that Aduhelm reduces amyloid plaque. Continued approval can depend on verification of clinical benefit in the required postmarketing study.

That approach allows patients access now rather than waiting several more years for another trial, but it also transfers much of the uncertainty from the preapproval process into routine medical care.

The advisory process exposed deep disagreement

The dispute did not begin this week. FDA convened its Peripheral and Central Nervous System Drugs Advisory Committee last November to review the application after Biogen revived the program following the earlier futility decision. The company’s advisory-committee notice described a public review of the evidence supporting the biologics license application.

Independent advisers were highly skeptical that the clinical data established effectiveness. That disagreement made Monday’s approval especially consequential because FDA ultimately relied on a rationale — amyloid reduction as a surrogate likely to predict benefit — that did not require the agency to conclude that the two Phase 3 trials themselves definitively proved clinical efficacy.

The Institute for Clinical and Economic Review issued a sharply critical June 7 statement, arguing that current evidence is insufficient to show patient benefit and that another trial should have come before broad availability. ICER said the decision effectively shifted the regulatory standard from demonstrated clinical outcomes to amyloid removal despite continuing uncertainty about how reliably that surrogate predicts slower cognitive decline.

Patients and advocates see time differently

The Alzheimer’s Association reached the opposite conclusion about the practical significance of the decision. In a statement welcoming approval, the organization described the drug as an important first step toward treatments that change the course of Alzheimer’s rather than merely treating symptoms.

That difference in perspective reflects the brutal reality of the disease. Alzheimer’s is progressive and irreversible with current therapy, and patients diagnosed today do not have the luxury of waiting indefinitely for a perfect evidence base. Families who have watched available treatments fail to alter the trajectory of decline may accept uncertainty differently from regulators, insurers or researchers evaluating population-level evidence.

Biogen CEO Michel Vounatsos called the approval a historic moment in a June 7 letter, arguing that the decision opens a new chapter in Alzheimer’s treatment and could stimulate additional research into disease-modifying therapies.

Those hopes are real, but so are the limits of the evidence. Aduhelm is not a cure, does not restore lost memory and has not been shown to reverse established dementia. The central question is whether long-term treatment meaningfully slows decline and for which patients.

Safety and monitoring will complicate routine use

FDA’s approval information warns about amyloid-related imaging abnormalities, or ARIA, which can include temporary swelling in the brain and small areas of bleeding. Many cases are asymptomatic, but some patients can experience headache, confusion, dizziness, visual changes or nausea.

That means treatment is not simply a monthly infusion. Patients may require magnetic-resonance imaging and careful clinical monitoring, adding complexity and cost beyond the drug itself. Neurologists and health systems must decide which patients are appropriate candidates while explaining an unusually complicated benefit-risk profile.

A contemporaneous Washington Post report described the approval as one of FDA’s most contentious decisions in years, noting both the enthusiasm of patients and advocates and the objections of researchers who believe the evidence is too uncertain. Biogen said the annual list price would be $56,000 before discounts or insurance, raising immediate questions about Medicare spending, coverage rules and access.

The confirmatory trial now carries enormous weight

Accelerated approval is not supposed to end the evidentiary process. FDA can require a postapproval trial and can begin proceedings to withdraw a drug if the expected clinical benefit is not verified. For Aduhelm, that requirement is central rather than peripheral because the approval rests on the judgment that amyloid reduction is reasonably likely to predict improved clinical outcomes.

The challenge is that conducting a placebo-controlled trial may become harder after approval. Patients who can obtain the drug outside a study may be less willing to enroll in a trial in which they could receive placebo. Regulators and Biogen will therefore need a study design capable of answering the clinical question while the treatment is commercially available.

The approval also has implications beyond one drug. Other companies are developing antibodies and other treatments that target amyloid or different biological mechanisms. If Aduhelm’s confirmatory study shows that plaque reduction produces meaningful clinical benefit, it could strengthen a therapeutic strategy that has endured years of failed trials. If it does not, the decision will intensify questions about whether the surrogate was an adequate basis for approval.

For patients and clinicians, those future answers do not yet exist. This week’s decision creates something Alzheimer’s medicine has lacked for years — a new disease-targeting option — but it does so with an unusually explicit degree of uncertainty. The next chapter will be written not only in infusion centers, but in the confirmatory evidence needed to determine whether the biological effect that won approval actually changes the lives of people with Alzheimer’s disease.