What Are the Side Effects of Stem Cell Therapy?

Published August 31, 2026. Most reported side effects of stem cell therapy are short-lived and local: swelling and pain where the injection was given, usually settling within four weeks. In a 2024 systematic review of 1,924 patients who received stem cell-based knee injections, 12.3% experienced a transient adverse event, and no infections, embolisms, or deaths were reported (Riggle et al., 2024). Serious harms have been documented, but almost entirely in connection with unapproved products sold outside clinical trials (Bauer et al., 2018).

What This Means

Two very different risk pictures get filed under the same phrase. One is the risk of the injection itself, measured in published clinical studies with defined protocols and follow-up. The other is the risk of buying an unapproved biologic product from a clinic that has not disclosed what is in the vial. The first is modest and mostly self-limiting. The second has produced blindness, bacterial infection, and death (Bauer et al., 2018).

Separating those two is the single most useful thing a patient can do before agreeing to anything.

Who Should Be Evaluated

Side-effect risk is not evenly distributed. It depends on the joint or structure involved, the cell source, whether the person has an active infection or uncontrolled diabetes, whether they take anticoagulants, and whether an accurate working diagnosis exists at all. A person with a history of cancer, an active systemic infection, or a bleeding disorder needs a different conversation than someone with isolated knee osteoarthritis.

Anyone considering a regenerative procedure should be evaluated in person by a licensed physician before any product is discussed as an option. Candidacy is a clinical determination, not a checkbox on an intake form.

What a Clinical Evaluation Includes

An evaluation at PrimeCell Regenerative includes a musculoskeletal and neurological exam, a review of prior imaging and records, and diagnostic ultrasound when it is appropriate. The point is to identify which structure is generating the symptoms before anything is recommended. Pain in a knee can come from the joint surface, the meniscus, a tendon, or be referred from the hip, and often from two of those at once.

Options Worth Comparing

Regenerative procedures are one column in a wider table. For knee osteoarthritis, the conventional pathway is structured exercise and physical therapy, weight management, oral anti-inflammatory medication, bracing, corticosteroid injection, and hyaluronic acid injection, with joint replacement for people who have exhausted non-operative care (Riggle et al., 2024). Platelet-rich plasma sits between the conventional and regenerative categories.

Each of those carries its own side-effect profile. A fair comparison puts the risks of a regenerative procedure next to the risks of the alternatives, not next to zero.

Benefits, Limitations, and Risks

The most frequently reported side effects are swelling and pain at the injection site. In the 2024 review, rates varied substantially by cell source: 51.7% for umbilical cord-derived injections, 29.5% for cultured adipose-derived cells, 10.7% for bone marrow-derived cells, and 8.1% for stromal vascular fraction (Riggle et al., 2024). Most of these resolved in under four weeks.

Beyond the injection itself, the risks that have caused real harm come from product quality and marketing. The FDA has documented serious adverse events in patients given unapproved products marketed as containing exosomes, and has warned that such products may be contaminated or have other quality defects (U.S. Food and Drug Administration, 2019). A separate review of unproven stem cell interventions catalogued adverse events including infection, tumor formation, and vision loss across clinics in 14 countries (Bauer et al., 2018).

There is also an indirect risk the FDA names explicitly: pursuing an unproven product can delay an accurate diagnosis and postpone care that is known to work (U.S. Food and Drug Administration, 2024).

What the Evidence Shows

The evidence does establish that intra-articular stem cell-based injections for knee osteoarthritis, in the short term, have not produced major complications such as sepsis, embolism, or death in the published clinical literature, and that local swelling and pain are common and usually transient (Riggle et al., 2024).

The evidence does not establish long-term safety. The authors of that review say so directly: further long-term studies are needed before a safety profile can be considered settled. The included studies were heterogeneous in protocol, formulation, and follow-up, and were level II through IV evidence rather than large randomized trials. Nor does the evidence establish safety for products, doses, or conditions outside what was studied.

Regulatory status is separate from evidence. The only stem cell products approved by the FDA in the United States are blood-forming stem cells derived from umbilical cord blood, approved for disorders affecting blood production. The FDA states that no such products are approved for any orthopedic condition, including osteoarthritis, tendonitis, disc disease, or back, hip, knee, neck, or shoulder pain, and that there are no approved exosome products (U.S. Food and Drug Administration, 2024). Anything offered outside that narrow approval is investigational.

Recovery and What to Watch For

Where swelling and soreness occur, they typically build over the first few days and settle within four weeks (Riggle et al., 2024). Relative rest, ice, and activity modification are the usual measures.

Contact the treating physician promptly for fever, spreading redness or warmth, drainage, worsening pain after an initial improvement, or any new neurological symptom. These are the findings that separate an expected local reaction from something that needs to be evaluated. Adverse events can also be reported directly to the FDA through its MedWatch program (U.S. Food and Drug Administration, 2024).

Florida and Orlando Considerations

Florida law changed in 2025. Section 458.3245 of the Florida Statutes permits licensed physicians to perform stem cell therapy that is not FDA-approved when it is within their scope of practice and relates to orthopedics, wound care, or pain management (Fla. Stat. § 458.3245, 2025).

The statute attaches conditions worth knowing as a patient. Cells must come from an FDA-registered facility accredited by one of four named bodies, and a post-thaw viability report for that product lot must reach the physician before use. The physician must obtain signed consent stating the nature of the procedure, that it is not FDA-approved, the recognized serious risks and complications, the alternatives including non-treatment, and encouragement to consult a primary care provider first. Advertising must carry a specific statutory notice (Fla. Stat. § 458.3245, 2025).

A patient in Orlando can reasonably ask to see the accreditation details and the viability report. A practice operating within the statute will have them.

Frequently Asked Questions

Do side effects differ depending on where the cells come from?

Reported rates did differ by source in the 2024 review. Umbilical cord-derived and cultured adipose-derived injections had significantly higher rates of local adverse events than bone marrow-derived cells or stromal vascular fraction (Riggle et al., 2024). Those were rates of swelling and injection-site pain, not serious complications.

How long does injection-site swelling usually last?

In the published studies, most local reactions resolved within four weeks (Riggle et al., 2024). Swelling that is worsening rather than improving after the first week should be evaluated.

Is stem cell therapy FDA-approved?

Only for a narrow use. Blood-forming stem cells from umbilical cord blood are approved for disorders affecting the blood-forming system. No stem cell or exosome product is FDA-approved for orthopedic or musculoskeletal conditions (U.S. Food and Drug Administration, 2024). Florida law permits physicians to perform non-approved stem cell therapy for orthopedic, wound care, and pain management indications under the conditions described above, but state permission is not federal approval.

What should I ask before agreeing to a procedure?

Ask what the product is and where it comes from, whether the source facility is FDA-registered and accredited, whether a post-thaw viability report exists for the lot, what the published evidence shows for this specific condition, what the alternatives are, and what happens if it does not help. Ask whether the FDA has reviewed the product and, if it is offered under a clinical trial, ask for the Investigational New Drug number (U.S. Food and Drug Administration, 2019).

This article is general education and is not medical advice, and it does not create a physician-patient relationship. Stem cell and other regenerative products discussed here are investigational for musculoskeletal use and are not FDA-approved to diagnose, cure, mitigate, treat, or prevent any disease. Individual results vary. Care options are discussed after a medical evaluation.

Medically reviewed by Kenny Chantasi, DO.

References

Bauer, G., Elsallab, M., & Abou-El-Enein, M. (2018). Concise review: A comprehensive analysis of reported adverse events in patients receiving unproven stem cell-based interventions. Stem Cells Translational Medicine, 7(9), 676-685. https://doi.org/10.1002/sctm.17-0282

Fla. Stat. § 458.3245 (2025). Stem cell therapy. The Florida Senate. https://www.flsenate.gov/Laws/Statutes/2025/458.3245

Riggle, C., McLellan, M., Bohlen, H., & Wang, D. (2024). Complications of stem cell-based injections for knee osteoarthritis: A systematic review. HSS Journal, 21(4), 476-484. https://doi.org/10.1177/15563316241271058

U.S. Food and Drug Administration. (2019, December 9). Public safety alert due to marketing of unapproved stem cell and exosome products. https://www.fda.gov/safety/medical-product-safety-information/public-safety-alert-due-marketing-unapproved-stem-cell-and-exosome-products

U.S. Food and Drug Administration. (2024, April 9). Consumer alert on regenerative medicine products including stem cells and exosomes. https://www.fda.gov/vaccines-blood-biologics/consumers-biologics/consumer-alert-regenerative-medicine-products-including-stem-cells-and-exosomes

Last medically reviewed: August 31, 2026

Related reading

• How Long Is Recovery After Stem Cell Therapy?
• Is Stem Cell Therapy Legal in the U.S.?
• How Does Stem Cell Therapy Work?
• PRP vs. Stem Cell Therapy in Orlando: Which Is Right for You?

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PrimeCell is a physician-led practice in Orlando. Candidacy for any procedure is determined at an in-person evaluation.