TL;DR
For decades, Alzheimer's drugs have been tested on people whose memories were already slipping, which may be the main reason so many have failed. A new federally funded trial flips that around. ARPA-H, the U.S. agency for high-risk health research, is putting up to $41 million into a four-year, 20-site trial that will try five to ten ways of heading off Alzheimer's at once, in people who have few or no symptoms but whose blood already shows the disease's early changes. Instead of waiting years to count who develops dementia, it will read a handful of blood markers, so a regimen that does nothing can be dropped fast and a promising one moved forward. If the approach works, preventing Alzheimer's could someday look less like a heavy infusion schedule and more like a pill, a supplement or a drug already sitting on pharmacy shelves, chosen with the help of a blood test.
Below the line, for paid subscribers: The full story: where it stands, how we got here and what's dated next; our Odds board on 5 milestones, starting with "An Alzheimer's prevention regimen is approved for people without symptoms"; our labeled speculation on what it adds up to; and every source.