Despite a Food and Drug Administration warning that draining blood from young folk and infusing it into older people might be harmful, startup Ambrosia says it has resumed doing just that.

The exsanguination enterprise earlier this year stopped selling young blood by the liter to old people and filling them up with it, immediately after the FDA issued an advisory that blood-plasma transfusions offered in the U.S. “should not be assumed to be safe or effective” and that consumers should be strongly discouraged from “pursuing this therapy outside of clinical trials under appropriate institutional review board and regulatory oversight.”

Ambrosia was founded in 2016 by Stanford Medical School graduate Jesse Karmazin, who has never been licensed to practice medicine. His company was reported to have been selling transfusions — at $8,000 per liter of plasma or $12,000 for two liters — at the start of this year in five cities including San Francisco.

Plasma is the largest component of human blood, and when separated out, it is a light-yellow liquid.

As of Friday, Ambrosia’s single-page website said the company was offering transfusions at its San Francisco clinic only, for the same prices reported earlier.

The Florida-based firm claims its transfusions can fight aging. Karmazin in a 2017 conference speech said, “We’re a company interested in making you young again.” Calling its offering “young plasma treatments,” Ambrosia says it uses blood from donors aged 16 to 25.

Karmazin, who worked for about two years as a medical resident but then moved into entrepreneurship without becoming a licensed physician, said last year that an Ambrosia study found the treatments led to a 20 percent drop in levels of two proteins, one linked to cancer and one to Alzheimer’s, The Guardian reported last year. The median age of participants in the study was 60, according to The Guardian.

Now, Ambrosia has resumed services, according to digital newsmagazine OneZero. “Our patients really want the treatment,” Karmazin told OneZero. “Patients are receiving plasma transfusions from donors ages 16 to 25 again.”

He said the FDA didn’t contact him before or after it issued the warning, and has taken no enforcement action against his company. He had stopped the transfusions out of “an abundance of caution,” he said, adding that he’s subsequently been in communication with the agency.

Karmazin would not tell OneZero how many customers Ambrosia has served, but said blood recipients ranged in age from their 30s to 90s, and some of them were healthy.

Doctors under contract perform the transfusions, and the blood is obtained from licensed blood banks in the U.S., he said. He told OneZero his company could legally conduct transfusions “off label,” meaning a doctor can prescribe them for something other than an approved use.

The FDA, according to the magazine, appeared to disagree. Though the agency said it does not comment on particular companies, it stated that it “has not licensed or approved any plasma product obtained from young donors for any use.”