Taking a young person’s plasma and infusing it into an older person to ward off aging — a therapy that’s fascinated some of the biggest names in Silicon Valley — has no proven clinical benefit, the Food and Drug Administration said.

The agency issued a safety alert on Tuesday about the infusion of plasma from young donors for the prevention of conditions such as aging or memory loss, or for the treatment of such conditions as dementia, Parkinson’s disease, multiple sclerosis, Alzheimer’s disease, heart disease or post‐traumatic stress disorder.

“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,” the FDA said in a statement from Commissioner Scott Gottlieb and Peter Marks, head of the agency’s biologics center.

The idea of infusing young blood to fight aging has attracted technology entrepreneurs like billionaire Peter Thiel and was lampooned in a 2017 episode of the HBO show “Silicon Valley.” Thiel’s reported interest was sparked by a company called Ambrosia, which has locations in five states across the U.S. and sells one liter of blood plasma from donors between the ages of 16 and 25 for $8,000, according to its website.

Gottlieb and Marks said none of the plasma treatments has gone through the rigorous testing required by the agency. Ambrosia says “experiments in mice called parabiosis provided the inspiration to deliver treatments with young plasma.” The FDA approval typically requires human trials before companies can make a specific health claim about a product.

“The reported uses of these products should not be assumed to be safe or effective,” Gottlieb and Marks said. “We strongly discourage consumers from pursing this therapy outside of clinical trials under appropriate institutional review board and regulatory oversight.”

Plasma, the liquid portion of blood, contains proteins to help the blood clot. Plasma infusion is an approved use by the FDA in trauma settings or in patients whose blood doesn’t coagulate. But, the FDA says, there are risks, including allergic reactions, circulatory overload, lung injury and infectious disease transmission.

“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 and Marks said. “Such treatments have no proven clinical benefits for the uses for which these clinics are advertising them, and are potentially harmful.”