WASHINGTON, DC, United States (AP) — US health officials on Friday approved a closely watched Alzheimer’s drug that moderatley slows the brain-robbing disease, albeit with potential safety risks that patients and their doctors will have to carefully weigh.

The drug, Leqembi, is the first that’s been convincingly shown to slow the decline in memory and thinking that defines Alzheimer’s by targeting the disease’s underlying biology. The Food and Drug Administration approved it for patients with Alzheimer’s, specifically those with mild or early stage disease.

Leqembi, from Japan’s Eisai and its US partner Biogen, is a rare success in a field accustomed to failed experimental treatments for the incurable condition. The delay in cognitive decline brought about by the drug likely amounts to just several months, but some experts say it could still meaningfully improve people’s lives.

“This drug is not a cure. It doesn’t stop people from getting worse but it does measurably slow the progression of the disease,” said Dr Joy Snider, a neurologist at Washington University in St Louis. “That might mean someone could have an extra six months to a year of being able to drive.”

Snider stressed that the medicine, pronounced “leh-KEM-bee”, comes with more than one downside, including the need for twice-a-month infusions and possible side effects like brain swelling.

The FDA approval came via its accelerated pathway, which allows drugs to launch based on early results before they’re confirmed to benefit patients. The agency’s use of that shortcut approach has come under increasing scrutiny from government watchdogs and congressional investigators.

Last week a congressional report found that FDA’s approval of a similar Alzheimer’s drug called Aduhelm — also from Biogen and Eisai — was “rife with irregularities”, including a number of meetings with drug company staffers that went undocumented.

Scrutiny of the new drug, known chemically as lecanemab, will likely mean most patients won’t start receiving it for months, as insurers decide whether and how to cover it.

The drug will cost about US$26,500 for a typical year’s worth of treatment. Eisai said the price reflects the drug’s benefit in terms of improved quality of life, reduced burdens for caregivers, and other factors. The company pegged its value at over US$37,000 per year but said it priced it lower to reduce costs for patients and insurers. An independent group that assesses drug value recently said the drug would have to be priced below US$20,600 per year to be cost-effective.

Some six million people in the US and many more worldwide have Alzheimer’s, which gradually attacks areas of the brain needed for memory, reasoning, communication and daily tasks.

The FDA’s approval was based on one mid-stage study in 800 people with early signs of Alzheimer’s who were still able to live independently or with minimal assistance.

Since then, Eisai has published the results of a larger 1,800-patient study that the FDA will review to confirm the drug’s benefit, paving the way for full approval later this year.

The larger study tracked patients’ results on an 18-point scale that measures memory, judgment and other cognitive abilities. Doctors compile the rating from interviews with the patient and a close contact. After 18 months, patients receiving Leqembi declined more slowly — a difference of less than half a point on the scale — than patients who received a dummy infusion. The delay amounted to just over five months.

There is little consensus on whether that difference translates into real benefits for patients, such as greater independence.

“Most patients won’t notice the difference,” said Dr Matthew Schrag, a neurology researcher at Vanderbilt University. “This is really quite a small effect and probably below the threshold of what we’d call clinically significant.”

Schrag and some other researchers believe a meaningful improvement would require at least a difference of one full point on the 18-point scale.

Leqembi works by clearing a sticky brain protein called amyloid that’s one hallmark of Alzheimer’s. But it’s not clear exactly what causes the disease. A string of other amyloid-targeting drugs have failed and many researchers now think combination treatments will be needed.

Aduhelm, the similar drug, was marred by controversy over its effectiveness.

The FDA approved that drug in 2021 against the advice of the agency’s own outside experts. Doctors hesitated to prescribe the drug and insurers restricted coverage.

The FDA did not consult the same expert panel before approving Leqembi.

While there’s “less drama”, surrounding the new drug, Schrag said many of the same concerns apply.