The $6 Billion Question: Do Alzheimer's Blockbuster Drugs Actually Work?
A sweeping new review of 17 clinical trials says anti-amyloid Alzheimer's drugs provide no meaningful benefit to patients, directly challenging the multibillion-dollar bet behind lecanemab and donanemab. The Alzheimer's establishment is pushing back hard, but the cracks in the amyloid hypothesis are getting harder to ignore.
A new report just called the most expensive bet in neuroscience a bust.
A sweeping evidence review concluded that anti-amyloid Alzheimer's drugs provide modest clinical benefits at best, with debate raging over whether those benefits are meaningful to patients. That's a grenade lobbed straight at a market projected to hit $33 billion by 2034.
The drugs in question, lecanemab (sold as Leqembi by Eisai and Biogen) and donanemab (Lilly's Kisunla), are supposed to represent a new era in Alzheimer's treatment. They're the first therapies that go after the disease itself rather than just managing symptoms. Medicare covers them. Billions of R&D dollars back them. And now a team of researchers is saying the emperor has no clothes.
What the Report Actually Found
The researchers looked at a whole class of drugs designed to clear amyloid beta, the sticky protein that clumps into plaques in Alzheimer's brains, analyzing clinical trials covering patients with mild cognitive impairment or mild dementia due to Alzheimer's.
Their conclusion was blunt: the drugs successfully remove amyloid from the brain, but that removal doesn't translate into meaningful cognitive improvement. Think of it like cleaning the rust off a car engine that still won't start. The rust might be part of the problem, but removing it alone doesn't fix anything.
Worse, the reviewers flagged that these drugs likely increase the risk of brain swelling and bleeding, a side effect known as ARIA (amyloid-related imaging abnormalities). The report recommended that future research pivot away from amyloid entirely, arguing that more trials targeting the protein are "unlikely to provide clear patient benefit."
The Numbers That Started the War
To understand why this report is so controversial, you need to understand the gap between "statistically significant" and "clinically meaningful." Those are very different things.
Lecanemab's landmark CLARITY AD trial showed a 27% slowing of cognitive decline versus placebo at 18 months. That sounds impressive until you look at the raw numbers: on the CDR-SB scale (the standard ruler for measuring Alzheimer's progression), lecanemab patients declined by 1.21 points at 18 months while placebo patients declined by 1.66 points. The actual difference? About half a point on an 18-point scale.
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Donanemab told a similar story. Over three years, early-start participants showed a 1.2-point advantage over controls on that same scale.
Prof Rob Howard of UCL put it plainly: the benefits are "too small to notice."
The Alzheimer's Establishment Fights Back
The Alzheimer's Association didn't take this lying down. They fired back with their own real-world data, claiming the drugs demonstrate "clinically meaningful slowing of disease progression" with "modest side effects" in early-stage patients. Multiple regulatory agencies worldwide approved these treatments, they pointed out, based on rigorous trial data.
Prof Sir John Hardy of UCL's Institute of Neurology offered a more measured defense: "Lecanemab and donanemab have shown us that slowing Alzheimer's is possible, representing genuine progress. They are not perfect, but they have opened the door to a new era of treatment."
Longer-term data from lecanemab does offer some hope. In a prespecified subgroup analysis of the open-label extension at four years, 81% of those patients remained in early stages of the disease rather than progressing to moderate or severe dementia, though this figure comes with caveats about patient dropout. A subset of patients with low tau levels did even better: 69% showed no worsening at all over four years.
So who's right? That depends on whether you think "slowing the decline" is the same as "making a difference patients can feel."
The Amyloid Hypothesis: Cracking Foundation
This debate isn't just about two drugs. It's about the entire intellectual framework that produced them.
The amyloid hypothesis has dominated Alzheimer's research for decades. The idea is straightforward: amyloid plaques cause the disease, so remove the plaques and you treat the disease. Amyloid-related projects have consumed a dominant share of the NIH's Alzheimer's funding.
But the cracks have been widening for years. About 30% of cognitively normal older adults have substantial amyloid plaque buildup in their brains, yet they think and remember just fine. That's a pretty inconvenient fact for a theory that says plaques cause dementia.
Then there's the fraud problem. A landmark 2006 study linking a specific form of amyloid to memory loss was retracted in 2024 after investigators found fabricated images. Scientists who've pushed alternative theories complain about being sidelined by what some call the "amyloid mafia," a research establishment so invested in one idea that competing hypotheses get starved of funding.
What Else Could Be Causing Alzheimer's?
Researchers are increasingly exploring a menu of alternative (and complementary) targets:
Tau tangles, another protein that accumulates alongside amyloid and may better explain nerve cell death
Neuroinflammation, where the brain's immune response goes haywire and starts damaging healthy tissue
Immune system dysfunction as a primary driver, not just a secondary effect
Viral infections that may trigger or accelerate the disease cascade
Nobel laureate Christof Südhof has warned that amyloid-lowering treatments, while modestly slowing decline, might actually hinder development of more transformative therapies by absorbing so much funding and attention.
Follow the Money
This is where things get really interesting. The Alzheimer's drug market is projected at roughly $5 to $12 billion in 2025, depending on whose estimate you trust. Anti-amyloid antibodies like Leqembi and Kisunla are forecasted to generate $2.9 billion and $2.3 billion in global sales, respectively.
Medicare currently covers both drugs under a "Coverage with Evidence Development" framework, meaning patients can access them as long as their doctors participate in an approved registry collecting real-world data. Private insurers like UnitedHealthcare and Aetna have followed suit with their own coverage policies.
But the UK's NICE (their version of a national cost-effectiveness watchdog) already rejected NHS funding for both drugs, citing small effects, significant side effects, and high costs. Dr. Sebastian Walsh of Cambridge welcomed that decision.
If other payers start reaching similar conclusions (and this new report gives them plenty of ammunition), the revenue projections that Wall Street loves could start looking very different.
The Billion-Dollar Bet Isn't Over Yet
Drugs targeting amyloid oligomers, a subtly different form of the protein, are in clinical development. If they fail, one prominent researcher noted, "the amyloid hypothesis is very much under duress." That's the polite version of saying it's dead.
But if even one succeeds convincingly, it could validate the approach and silence the critics. The next two years will tell us whether the biggest bet in neuroscience history was visionary or just very, very expensive wishful thinking.
For the 55 million people worldwide living with dementia, the answer can't come soon enough.
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