There remains, in the medical community, a disagreement over what exactly causes Alzheimer’s disease. If you even look at what kinds of drugs people are trying to make to treat the disease, there is no consensus on what mechanism the drugs should target.

The above picture was taken from “History and progress of hypotheses and clinical trials for Alzheimer’s disease” by Liu et al in 2019. This picture shows all the different clinical trials being run on Alzheimer’s disease, and all the different kinds of drugs people are using in those clinical trials. What’s interesting is that those drugs don’t all target the same or even similar things. Some drugs target Amyloid Beta, some target Tau, some target things you may never have heard of, like Neurotransmitters or the Mitochondrial Cascade. In most diseases we know what causes the disease, ever drug that has a clinical trial to treat COVID will in some way be targeting the coronavirus itself, because that’s what causes COVID. But there is no consensus on what causes Alzheimer’s disease, so the drugs that are in clinical trials all target completely different things.

With no consensus, it’s hard to see a path forward for both research and drug discovery. There are a number of antibody-based drugs on the market today which are supposed to clear our either Amyloid Beta plaques or Tau tangles, but there’s no consensus in the field if those are even the causative agents of Alzheimer’s disease. So if you’re a drug company investigating this, you’d making a bet not only that your product will do what it’s supposed to (clear out tangles and plaques) but you’re ALSO making a bet that you know the One True Cause of Alzheimer’s disease and that 70% or researchers are just wrong when they think the causative agent might be something else.

I’m not saying this is entirely a bad thing, I think it’s good that researchers and drug discovery companies are willing the gamble big to cure Alzheimer’s disease, despite knowing that the science isn’t even settled on what causes Alzheimer’s disease. But I am saying that I’m not exactly surprised that we’ve been studying this for decades with no effective cures in sight.