For two decades, Alzheimer's research has focused solely on the idea that amyloid plaques on the brain are what cause the disease. Some have even suggested that there's a "cabal" of researchers who have kept other theories from being explored in universities.

And yet all this amyloid research has resulted in 130 Alzheimer's drug failures over the last 20 years. This strongly suggests that maybe amyloid plaques don't cause Alzheimer's, after all.

For instance, some researchers have suggested that amyloid plaques are a kind of "scab on the brain," an attempt by the body to heal something that has gone wrong. Scientists have also noticed that many people with amyloid plaques on the brain do not have Alzheimer's. This suggests that the theory that fixing amyloid plaques will stop Alzheimer's is seriously flawed.

In a highly controversial decision, the Food and Drug Administration recently approved an Alzheimer's drug from Biogen (BIIB 4.56%), even though the drug had basically the same efficacy as placebo: In other words, no efficacy at all. Why did the FDA approve the drug, against the recommendations of all the doctors on the advisory panel? Because the drug successfully removes amyloid plaques. But if removing amyloid plaques doesn't help Alzheimer's patients, this drug approval is tragic, and maybe even dangerous. (Biogen's drug causes brain bleeds in some patients.)

All this failure following the amyloid hypothesis has caused a new wave of Alzheimer's drugs to finally show up, from small biotechs like Cassava Sciences (SAVA 0.93%)Anavex Life Sciences (AVXL -7.34%) and Annovis Bio (ANVS 7.24%).

Even Biogen is now doing research in other areas, implicitly acknowledging that the amyloid hypothesis is not getting the job done. Biogen's new focus is on lowering tau protein in Alzheimer's patients. Motley Fool editor and analyst Olivia Zitkus and writer Taylor Carmichael met virtually to discuss Biogen's new research. This video clip was recorded live on July 30.

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Taylor Carmichael: Right now, all they really know is that it reduces amyloid plaques.

Olivia Zitkus: Right.

Taylor Carmichael: But there's no evidence, there's no proof that amyloid plaques is what causes Alzheimer's. It's just there in Alzheimer's patients. The other thing about this drug, there are adverse events. It causes brain bleeds in some patients. Again, I'm not a doctor, but to me, the way I think of plaques is like a scab on the brain, and if you pick a scab, it's going to bleed. So it doesn't surprise me that this drug that is getting rid of these plaques on the brain is causing brain bleeds in some patients. So it's just another issue that there are adverse effects going on, they haven't proven efficacy, and they are asking $56,000 from insurers on an annual basis for this drug. So it's highly controversial.

Olivia Zitkus: That's a big price tag when you're not sure that your target is the right one. Part of the reason I wanted to talk about this today is because the Alzheimer's Association International Conference is just wrapping up today. It started on July 26 and wraps up today. At the conference, Biogen reported positive top-line data from a different drug combination. What do you know about this new report, which has a different profile and a different target? It's not even targeting those amyloid plaques you talked about.

Taylor Carmichael: Right. That's good, I think, because I don't think amyloid plaques is the answer. I don't think reducing amyloid plaques is the answer. This is a very early study. This is a phase 1 trial, so all we really know is safety. That's what you're looking at phase 1. Is it safe? They said it was, so they've proven safety. They did have some positive biomarker data. I believe it was in tau. It's past my knowledge when you start getting into deep chemistry. But they do have biomarker knowledge. This is very early: years away. Typically, I ignore phase 1 stuff. The one exception being COVID-19. COVID-19 phase 1 proved me wrong.

Olivia Zitkus: A little bit of a different story.

Taylor Carmichael: Yeah, it's clearly a different story, but typically, I like to wait until phase 2 data. Phase 3 data is the best, Phase 2 is when you start seeing excellent results. They don't have that yet, they're still years away, but it's always good to have things bubbling up in the pipeline.

Olivia Zitkus: Yeah. For this drug combination the the phase 1 study had the primary objective of like you said, safety and tolerability too in patients with mild Alzheimer's disease. Biogen did say that this study demonstrated time and dose dependent lowering of the tau, it's protein in cerebrospinal fluid, in CSF, over, I think, a three-month treatment period. Like you said, I think this is interesting. I think it says something about Aduhelm that they're now looking at the tau protein. It's interesting that they have a bunch of different targets happening and we'll have to see what happens there. I'll be waiting, I'm not a risky enough investor to jump in like you said on phase 1 data.