On Tuesday, the FDA issued a warning to anyone who might be inclined to give their old bones a jolt with fresh blood harvested from the young.

The idea is pretty far from mainstream, even in Silicon Valley, where the ultra-wealthy have a keen interest in the cutting edge of life-extension science. Still, there’s apparently enough buzz around the practice that the FDA is warning consumers of “unscrupulous actors” who tout the benefits of infusing patients with plasma extracted from youthful donors while extracting literal blood money from their clients:

We have significant public health concerns about the promotion and use of plasma for these purposes. There is no proven clinical benefit of infusion of plasma from young donors to cure, mitigate, treat, or prevent these conditions, and there are risks associated with the use of any plasma product. Today, we’re alerting consumers and health care providers that treatments using plasma from young donors have not gone through the rigorous testing that the FDA normally requires in order to confirm the therapeutic benefit of a product and to ensure its safety. As a result, the reported uses of these products should not be assumed to be safe or effective. We strongly discourage consumers from [pursuing] this therapy outside of clinical trials under appropriate institutional review board and regulatory oversight.

With the new warning, any companies pursuing the controversial and currently not scientifically supported practice are on notice. The best-known company in the field, Ambrosia Medical, reportedly began its own trials for young blood plasma transfusions back in 2017. The new FDA warning took direct aim at the company, which appears to have skirted regulations by leaning on the fact that blood transfusions are FDA-approved, even if the company’s fringe anti-aging applications are not.

On Tuesday, Ambrosia Medical’s sparse website displayed a single message: “In compliance with the FDA announcement issued February 19, 2019, we have ceased patient treatments.” TechCrunch has reached out to the company about its decision to stop operations in light of the FDA’s warning.

On top of the conspicuous absence of properly studied clinical benefits — “no compelling clinical evidence on its efficacy,” as the FDA puts it — fueling yourself up with young blood without government oversight is actually pretty dangerous. The straightforward danger of blood-borne pathogens is compounded by other risks around dosing.

“Plasma is not FDA-recognized or approved to treat conditions such as normal aging or memory loss, or other diseases like Alzheimer’s or Parkinson’s disease,” the FDA stated. “Moreover, reports we’re seeing indicate that the dosing of these infusions can involve administration of large volumes of plasma that can be associated with significant risks including infectious, allergic, respiratory and cardiovascular risks, among others.”

Ambrosia Medical appears to have wrapped up its initial study, “Young Donor Plasma Transfusion and Age-Related Biomarkers,” in January 2018 and stayed pretty quiet since. The study is registered with clinicaltrials.gov, though the research still appears to have operated beyond the bounds of the government’s institutional review and oversight process. In its warning, the FDA didn’t name Ambrosia Medical, instead referring to any entities in the young blood business as “companies that abuse the trust of patients and endanger their health.”

“As a general matter, we will consider taking regulatory and enforcement actions against companies that abuse the trust of patients and endanger their health with uncontrolled manufacturing conditions or by promoting so-called ‘treatments’ that haven’t been proven safe or effective for any use,” the FDA stated.