The US FDA is officially warning consumers that buying young blood infusions to improve their health is not a good idea

From FDA officially warns against buying young blood – The Verge:

The idea that infusions of young blood could slow aging has been around since the early 2000s, when studies in mice showed promising results. (Notably, the young and old mice weren’t just sharing blood; they were attached and actually shared organs, too.) The concept really gained traction a few years ago, thanks in part to a rumor that venture capitalist Peter Thiel was interested in the transfusions. As other sites, including Bloomberg have noted, despite the outlandish nature of the claim, jokes about vampirism, and a spoof on the show Silicon Valley, the idea has not gone away and young blood clinics do exist. Notably, a startup called Ambrosia Medical promised transfusions for $8,000 a liter. “It works,” Ambrosia founder Jesse Karmazin told a Mic reporter. “It reverses aging.”There is almost no evidence that this claim is true. Some of the researchers who did the original young blood studies have shown (again in mice) that old blood hurts more than young blood helps and suggest that it’d be a better idea to instead just study why old blood is harmful. In 2017, a rigorous clinical trial found that young blood given to 18 patients with Alzheimer’s did almost nothing to treat the disease. Not only is this ineffective, but even typical transfusions can be dangerous, leading to a few dozen deaths reported to the FDA each year.

Both Google (with Calico) and Jeff Bezos (with Unity Biotechnology) are researching this practice. I doubt that a rigorous study on just 18 patients for a very specific use case like Alzheimer would discourage them.