These Alzheimer's drugs were supposed to revolutionize the way we fight the disease. The reality is more complicated.

MW These Alzheimer's drugs were supposed to revolutionize the way we fight the disease. The reality is more complicated.

By Brett Arends

An estimated 7.2 million Americans age 65 and older were living with Alzheimer's dementia in 2025, according to the Alzheimer's Association.

A scientific report published this week has raised questions about how much Leqimbi and Kisunla - the "breakthrough" Alzheimer's drugs that have hit the market in the last few years - really help slow the disease.

These drugs produce "little or no difference in cognitive function ... dementia severity [or] functional ability," according to the report, published by the highly respected scientific nonprofit Cochrane Library. It added that their effect after 18 months is "trivial" at best.

As these drugs have given new hope to millions of people with dementia or cognitive impairment, and sales worldwide are skyrocketing, the implications are potentially huge. But how significant are they?

Researchers say the actual takeaways are more complicated.

The new report was not based on any updated research, but on a review of existing studies, researchers point out. It looked at recent drugs which try to fight Alzheimer's by removing the telltale protein clusters in the brain known as "amyloid plaques." And while the researchers looked at 17 different medical studies, only two of those related specifically to Leqembi and Kisunla; the others related to other drugs that targeted amyloid clusters.

An estimated 7.2 million Americans age 65 and older were living with Alzheimer's dementia in 2025, with no end in sight. Researchers estimate that if you are 55 or older, you have a 42% chance of getting it before you die. There is no cure, and the financial costs of caring for elders with dementia is enormous and rising as the population ages.

Researchers have struggled for generations to make any progress in treatments. There have been widespread hopes that drugs like Leqembi and Kisunla, which emerged just a couple of years ago, would mark the beginning of an era when the disease became treatable.

"This paper overall is scientifically flawed," says Michael Rosenbloom, a senior neurologist at the University of Washington's Medicine Memory and Brain Wellness Center. "Some of these drugs act in different ways. It's not like comparing apples to apples." Some of the studies that were reviewed had their own flaws and limitations, he added.

As expected, the manufacturers of the two drugs also challenged the findings, and their investors appeared unconcerned. Eli Lilly $(LLY)$, which makes Kisunla, was off 1.3% this week. Shares of Leqembi's developers, Biogen $(BIIB)$ and Japan's Eisai $(ESAIY)$ (JP:4523), were mixed; Biogen was up about 2.5% on the week, while Eisai's U.S.-listed ADRs shed 1.4%.

But Toby Lasserson, deputy editor in chief of the Cochrane Collection, which published the research, defended the paper. "Pooling data from similar drugs is a common method to provide a high-level overview of their risks and benefits," he tells MarketWatch. "It is inappropriate to dismiss the review's conclusions because it presented pooled outcomes as well as individual ones."

He added: "We advise authors to also analyze drugs separately where there may be differences, and these analyses were carried out for this review."

Meanwhile Bryce Vissel, a senior neuroscientist at the University of New South Wales in Australia, says the Cochrane report raises important questions about whether researchers are right to try to fight dementia by targeting amyloid plaques.

"Alzheimer's is the progressive failure and loss of synapses and nerve cells, which patients experience as failing memory, failing thinking and lost independence," Vissel tells MarketWatch. "We and our collaborators have been raising concerns in the scientific literature for years about the dominance of the amyloid hypothesis. We have long argued that while amyloid has [a] role in the disease, it alone does not explain Alzheimer's dementia."

For the rest of us, the important news about dementia to have come out in recent years is probably from the Lancet Commission of medical research experts, which argues that we can cut our risk of getting dementia nearly in half by pursuing healthier lifestyle choices - including maintaining a healthy weight, avoiding tobacco or excess alcohol, doing more exercise, and taking steps to address chronic depression and social isolation.

-Brett Arends

This content was created by MarketWatch, which is operated by Dow Jones & Co. MarketWatch is published independently from Dow Jones Newswires and The Wall Street Journal.

(END) Dow Jones Newswires

April 18, 2026 09:00 ET (13:00 GMT)

Copyright (c) 2026 Dow Jones & Company, Inc.