The donated blood typically comes from teenagers, although anyone under the age of 25 is eligible. The company buys its supply from blood banks, which also sell blood to pharmaceutical companies. So high-schoolers donating their blood are not aware that their blood might be used on healthy adults.

Speaking to a roomful of technologists, Karmazin explained that the company does not claim that it can cure aging in humans. Instead, he’s hoping to recruit hundreds more people to research whether the transfusions can help fight particular symptoms associated with aging. Traditionally, biological aging hasn’t been treated as a disease, which makes it challenging to study.

Karmazin said those who have signed up so far have seen some positive benefits, and haven’t reported any negative ones. Blood transfusions come with a variety of potential risks, including allergic reactions.

Karmazin started the company after reviewing research into whether injecting older mice with the plasma portion of young ones can improve memory. Older, so-called parabiosis studies, went a step further in connecting older and younger animals so that their blood mingles.

These studies are far from definitive, and scientists have spoken out about the ethics of such a study, which they see as taking advantage of the public’s excitement and lacking much evidence. But the concept has seen a recent resurgence in interest as well-known Silicon Valley investors like Peter Thiel have spoken out about its promise.

But that does not mean that Thiel gets teenage blood transfusions, said Karmazin, a graduate of Stanford Medical School. Karmazin stressed that Thiel is not an Ambroisa customer — and to his knowledge, Ambrosia is the only U.S. company on the market.

“Of course, it’s possible he could have gone abroad,” Karmazin shrugged. “But I haven’t heard anything about that.”