The clinics make promises that aren't borne out by the level of research that's gone into stem cell therapies.
The clinics don't have the equipment to fully separate stem cells from the tissue samples they take from their patients. The result is that these patients are likely getting injected with a mixture including stem cells, plus a bunch of other types of cells, depending on the body part from which clinicians take the original tissue sample.
Some of the advertised procedures don't use stem cells at all. The Stanford team found clinics offering platelet-enriched plasma as stem cell therapy. Platelet-enriched plasma doesn't contain stem cells. Technically, platelets don't even count as cells. You can learn more about platelet-enriched plasma from our story about blood facials (yum).
Because they promote the growth of cells, stem cells may create unwanted growths, including tumors. How about this woman who grew nasal tissue on her spine after a stem cell transplant?