Businesses marketing purported stem cell treatments and exosome therapies for COVID-19: An analysis of direct-to-consumer online advertising claims.

We identified 38 businesses advertising purported stem cell interventions and exosome products for COVID-19. These companies operated or facilitated access to 60 clinics. More than 75% of these clinics were based in the United States and Mexico. Thirty-six of the businesses marketed their stem cell and exosome products as treatments for Long COVID, six advertised them as "immune boosters," five claimed to treat patients in the acute infection phase, and two claimed their products were preventive. The least expensive product cost $2,950, the most expensive was $25,000, and the average listed cost for patients was $11,322. The promotion of these products is concerning because they have not been approved by national regulators and do not appear to be supported by convincing safety and efficacy data.