When 68-year-old Mark Thompson* walked into a private clinic on the outskirts of Monterey, California, $8,000 in hand, he had one hope in mind: to leave the clinic feeling physically and mentally back in his prime.

The treatment? A single two-liter dose of plasma — the watery part of blood with all the cells removed — collected from anonymous young adult donors aged 25 and younger.

Thompson is one of the 30 healthy elderly adults who have accepted a hefty price tag to participate in a pay-to-play anti-aging clinical trial. The brainchild of Dr. Jesse Karmazin, a DC-based physician and entrepreneur, the trial hopes to use the blood of the young to battle aging — and anyone older than 35 is welcome to try it out.

If that all sounds crazy, you’re not alone. But a barrage of high-profile studies from the past five years is building compelling evidence to suggest youthful blood can turn back the aging clock and restore functions in multiple organs, at least in mice.

Karmazin’s startup Ambrosia — Greek for “immortality” — is betting on the chance these early results might translate into a human anti-aging elixir. Since 2016, working with Dr. David Wright who runs an intravenous therapy clinic in Monterey, Ambrosia has been steadily pumping single doses of donor plasma to those willing to pay.