The Food and Drug Administration has approved a drug that may help people in the early stages of Alzheimer's maintain their mental abilities.

Lecanemab, which will be marketed as Leqembi, is likely to reach many more patients than a similar product, Aduhelm, which flopped after receiving a controversial approval in 2021.

"This is a milestone for people eligible for this treatment, for their families, for the research community," says Maria Carrillo, chief science officer for the Alzheimer's Association.

But Leqembi, like Aduhelm, can cause swelling or bleeding in the brain, which means patients must receive periodic brain scans after starting treatment. It's also unclear whether Medicare and private health insurers will cover the drug, which is likely to cost tens of thousands of dollars each year.

Eisai, the company that developed Leqembi in partnership with fellow drugmaker Biogen, has said it will price the treatment at $26,500 per year.

The new drug, which is given intravenously every other week, removes a substance called amyloid from the brain. Sticky amyloid plaques are a hallmark of Alzheimer's, though many previous drugs that targeted amyloid failed to slow down patients' loss of mental abilities.

In a study of 1800 people with early Alzheimer's, those who got Leqembi for 18 months experienced 27 percent less decline in memory and thinking.

That's a modest benefit, says Dr. Joy Snider, a professor of neurology at Washington University School of Medicine in St. Louis.

"It's not a cure. It doesn't stop the disease completely. It doesn't make people get better," Snider says. "But it does slow down progression in very mild disease."

And even a modest slowing could be meaningful to patients and their families, says Snider, who helped conduct the study that found a benefit.

"Maybe you could keep driving for an extra six months or a year," she says. "Maybe you could keep doing your checkbook for an extra six months to a year."

It could be many months, though, before Leqembi reaches many of the millions of patients who might benefit.

To qualify for treatment, people need to undergo tests showing that they are in the early stages of dementia and that their brains contain the amyloid deposits that are a hallmark of Alzheimer's. That process is likely to include at least two visits to specialists, who are in short supply.

The result is likely to be a very long queue, says Jakub Hlávka, a health policy expert at the University of Southern California.

"Roughly speaking we can expect that to take about five years before all the currently eligible patients may get cleared through that queue," he says.

Leqembi received what's known as accelerated approval, a conditional okay to market a drug, based on its ability to remove amyloid from the brain. The FDA is likely to consider a full approval later this year, after reviewing the evidence that the drug also helps preserve mental function.

Carrillo is confident the drug will receive full approval.

"The science speaks for itself," she says. "The science is telling us that lowering amyloid is leading to clinical benefit."

But until Leqembi has full FDA approval, Medicare is unlikely to cover it for many patients. The reason has to do with the earlier Alzheimer's drug, Aduhelm.

After Aduhelm received accelerated approval in 2021, the Centers for Medicare and Medicaid Services ruled that Medicare would cover the drug only for patients enrolled in certain clinical trials. The agency said it was unwilling to offer wider coverage for an Alzheimer's drug that had not clearly shown it could preserve memory and thinking.

The ruling applies not just to Aduhelm, but to all Alzheimer's drugs that target amyloid and have not received full FDA approval.

So for now, most patients who want Leqembi will have to pay for it out of pocket.

"Without coverage, we are talking about a breakthrough that is not available to the American public," Carrillo says. "And that is not acceptable."

If Medicare and other payers do start covering Leqembi, the cost could be tens of billions of dollars a year, Hlávka says. The price tag is so high, he says, that payers and federal officials may want to consider a new approach to caring for people with dementia.

"One of the potential solutions would be to see if we can pool all of the dementia patients who are covered under different plans into a single risk pool and then provide coordinated access and care to those patients," Hlávka says.

That would allow the government to balance the cost of the drug against potential savings if people with dementia are able to delay expensive nursing home care, he says. It would also make it easier for the government to negotiate on the price of Leqembi.

There's a precedent for putting all people with a given disease under the same umbrella, Hlávka says.

Since the early 1970s, Medicare has run a special program for people of all ages whose kidneys are failing.