Bloodsucking startups, beware: The Food and Drug Administration is warning against commercial plasma transfusions.

The FDA issued a statement this month saying that such treatments, which have been marketed as a way to fight a variety of diseases, have no proven benefits and many potential risks. The FDA “strongly” discourages consumers from using this therapy outside of clinical trials, commissioner Scott Gottlieb said in a statement.

“Simply put, we’re concerned that some patients are being preyed upon by unscrupulous actors touting treatments of plasma from young donors as cures and remedies,” Gottlieb said.

Ambrosia Plasma, a treatment center that had provided such services, said on its website that as of Feb. 19 it would cease treatments to comply with the warning. The startup previously harvested plasma from individuals under the age of 25 and then transfused it to older customers, supposedly to combat the effects of aging and health issues. The center did not respond to a request for further comment. “Young blood is an exciting new therapy which shows promise for aging and the reversal of conditions such as Alzheimer’s disease,” Ambrosia claimed on its Facebook page.

Gottlieb wrote that plasma is not FDA-approved to treat issues like aging and memory loss, neither has it been approved to treat diseases like Alzheimer’s and Parkinson’s. Plasma transfusions can lead to problems including infections, allergic reactions and cardiovascular risks, the FDA said.

“Our concerns regarding treatments using plasma from young donors are heightened by the fact that there is no compelling clinical evidence on its efficacy, nor is there information on appropriate dosing for treatment of the conditions for which these products are being advertised,” he said.

Ambrosia has declined to publicly report costs for these transfusions, but the website Quartz reported that patients pay up to $8,000 for treatments during which they are infused with 1.5 liters of a young person’s blood over the course of two days.

This is not the only bloody beauty trend in recent years. “Vampire facials” have been on the rise after Kim Kardashian posted about them. The facial, which costs an average of $1,500 but can cost as much as $2,500 per treatment, involves drawing blood from a client, using a centrifuge to separate platelet-rich plasma (PRP) from red blood cells, and then reapplying the plasma to the face using microneedles, reportedly to promote cell renewal. Unlike the blood treatments condemned by the FDA, this procedure involves using a patient’s own blood rather than the blood of a donor. While the “vampire facial” practice was not part of the most recent FDA warning, no PRP treatments are approved for aesthetic use. Other FDA-approved procedures to make a patient look younger include Botox and Juvederm.

The FDA has also been cracking down on supplements and IV infusions claiming to treat Alzheimer’s disease and other serious illnesses like cancer and Parkinson’s. On Feb. 11 the FTC and FDA sent warning letters to companies claiming to treat HPV and cancer with vitamins. These companies were given 15 days to take actions responding to the FDA’s concerns.

In September 2018, the FTC declared that companies that sell vitamin IV services are not allowed to make unsupported promises about the effectiveness of their treatments for cancer and other illnesses.

This story was updated on Feb. 28, 2019.