That a drug hasn't been approved for a treatment in years is no reason to approve one that doesn't work.
It isn't a blanket approval, but it does sound way too generous in terms. From the linked article:
> The agency seems to have approved it based on its demonstrated ability to clear beta-amyloid, and is asking Biogen to run a confirmatory trial to show efficacy.
> They will be absolutely overjoyed to do that, of course, because the whole time that’s going, they will be selling the first drug that (in theory) targets the etiology of Alzheimer’s. The backed-up demand is going to be gigantic, and Biogen is going to make enormous amounts of money. They have nine years, as it turns out, to get this trial done, and I feel safe in predicting that it’s going to take alllll niiiiine loooong sloooow years to get this done.
This is a cop out decision by the FDA. Efficacy can be determined by a RCT - instead a decision was made which supports biogen’s share price