Stem cell therapy risks include infection, unwanted immune reactions, tumor formation and, in documented case reports, serious harm to the eyes and spinal cord. The risks depend heavily on the product, how it is prepared and where it is placed in the body.
This page summarizes what regulators and published case reports describe, as a companion to what is stem cell therapy. It is general education, not medical advice, and it does not say that any treatment works.
Why risk looks different for approved and unapproved products
The US Food and Drug Administration regulates regenerative medicine products. According to the agency’s patient and consumer information on regenerative medicine therapies, there is broad marketing of unapproved products intended for the treatment or cure of a wide range of diseases. Before approval, such products require FDA oversight in a clinical trial.
That oversight is a safety measure. The FDA has repeatedly notified manufacturers, clinics and health care practitioners of the need for Investigational New Drug applications to legally administer these products and to ensure safety measures are in place before administration. The agency says that unapproved regenerative products have risks but are often marketed as safe and effective even though they have not been adequately studied under such an application to demonstrate those claims.
The FDA’s patient and consumer information page, last updated in 2024, also states that the only stem cell products currently approved in the United States consist of blood-forming stem cells derived from umbilical cord blood, approved for disorders that affect the production of blood. On December 18, 2024, the FDA approved Ryoncil, a donor bone marrow-derived mesenchymal stromal cell therapy, for steroid-refractory acute graft-versus-host disease in children; the FDA’s list of approved cellular and gene therapy products is the current reference. The rest of this page concerns the wider set of unapproved products and procedures.
Safety concerns the FDA lists
The same FDA page lists specific safety concerns for any product illegally marketed as a regenerative medicine therapy. They fall into a few groups.
- Infection. Bacterial infections, including life-threatening blood infections, and cross-contamination with bacteria, viruses or mold related to how the product was prepared.
- Immune and inflammatory reactions. Unwanted inflammatory or immune response to the cell product, and reactions at the site where cells were collected or administered.
- Cells in the wrong place. Cells moving to another part of the body and turning into an unintended type of tissue or growing excessively, which the FDA describes as a way a tumor can form.
- Serious organ harm. Blindness and neurological events.
- Untested supply. A product may not have been tested for infectious diseases such as hepatitis and HIV.
- Missed alternatives. The therapy may fail to work as anticipated when approved treatments are available.
The FDA adds that it has received reports of blindness, tumor formation and infections linked to unapproved products, and it asks patients to report adverse events through its MedWatch program.
Case reports published in medical journals
Beyond regulatory warnings, peer-reviewed case reports describe harm after unproven procedures. A 2017 report in the New England Journal of Medicine described three patients who developed severe bilateral visual loss after receiving intravitreal injections of autologous adipose tissue-derived “stem cells” at a clinic in the United States. The authors linked the visual loss to problems including ocular hypertension, hemorrhagic retinopathy, vitreous hemorrhage, retinal detachment or lens dislocation, and the patients’ visual acuity after one year ranged from 20/200 to no light perception.
A separate 2016 letter in the same journal, titled Glioproliferative Lesion of the Spinal Cord as a Complication of “Stem-Cell Tourism”, described a glioproliferative lesion of the spinal cord as a complication of what the authors call stem-cell tourism. Case reports cannot show how common such events are, because they describe individuals rather than rates. They do show that serious complications are documented and that they can follow even a procedure described as using a patient’s own cells.
What case reports can and cannot show
A case report is a physician’s account of what happened to a small number of patients. It is useful as an early warning, because it can reveal a complication that no one had expected, and it often prompts regulators and researchers to look more closely at a practice. It cannot tell a reader how often the complication occurs, whether it would happen again under different conditions, or how the risk compares with that of other options.
That limit applies in both directions. The absence of published reports about a particular procedure does not demonstrate that the procedure is safe, since unregulated treatments are rarely tracked in any systematic way. The FDA’s request that patients report adverse events exists partly for this reason: without reports, harms stay invisible to the people who could study them.
Controlled clinical trials are the tool built to answer the questions case reports leave open. They enroll defined groups of participants, follow them over time, and record both benefits and harms in a way that can be compared. This is the reason regulators keep asking that new cell products be tested in trials with FDA oversight before they are offered to consumers.
Where the risks come from
The list above reflects several different sources of risk, and the same label can cover very different products.
- Preparation. Cells processed outside a controlled manufacturing setting can pick up contaminants. This is the source of the infection and cross-contamination concerns.
- Route of delivery. Placing cells into delicate tissue such as the eye or spinal cord brings procedure risks of its own, separate from the cells themselves.
- Cell behavior. Living cells can multiply or change type after injection, which is why tumor formation appears on the FDA’s list.
- Source of cells. Cells from another person’s body can provoke immune reactions, while the claim that cells from a person’s own body are automatically safe is not supported by the case reports above.
Reading risk claims critically
Marketing for cell products often leans on phrases such as “natural”, “your own cells” or “minimally invasive”. These describe where cells come from or how invasive an injection feels, not whether the specific use has been tested. The FDA also notes that patients are sometimes pointed to ClinicalTrials.gov, or told a product is registered with the agency, as a sign of compliance, and that this is often false because neither means the product is legally marketed.
The article on unproven stem cell clinics goes through warning signs in more detail, and the checklist of questions to ask before stem cell treatment lists what to ask a provider. Decisions about any treatment belong with a licensed physician who knows the reader’s medical situation and can explain the risks of both approved options and clinical trials.
Frequently asked questions
Can stem cell injections cause infections?
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The FDA lists bacterial infections, including life-threatening blood infections, as a safety concern for products illegally marketed as regenerative medicine therapies, along with contamination during processing.
Can stem cells form tumors?
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The FDA names tumor formation as a reported concern, describing cells that move to another part of the body or grow excessively. A published case letter also described a spinal cord lesion as a complication of stem-cell tourism.
Are treatments using a person’s own cells risk-free?
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No. The journal report on injections of fat-derived cells into the eye described severe vision loss in patients who had received their own cells.
Where can an adverse event be reported?
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The FDA encourages patients who were hurt or had a bad side effect after a regenerative medicine product to report it through its MedWatch Adverse Event Reporting program.
