Stem Cell Therapy Side Effects: Risks, Pain and Safety Explained

What are the side effects of stem cell therapy? In clinical trials the common side effects are short-lived: soreness, swelling and stiffness where the cells were injected and, after an IV infusion, a passing fever, which was the only adverse event more frequent than in control groups in a large review of intravenous trials (Thompson et al.). Serious harms such as blindness, tumors and infections have been reported, mainly with unapproved products prepared and used outside controlled settings (FDA). So the honest answer to “is it safe?” is: it depends on the product, the route and who makes the cells.

Common side effects by type of treatment

“Stem cell therapy” covers very different procedures, and the side effects follow the route, not the label.

Route	Expected side effects	What trials report
Injection into a joint or tendon	Pain, swelling and stiffness at the site, usually short-lived	In 8 randomized trials with 502 knee osteoarthritis patients, adverse events did not differ significantly from controls
Harvest of your own fat or bone marrow (when used)	Soreness and bruising at the harvest site	No serious events related to the cells in 9 trials, but complications from liposuction were observed
IV infusion	Fever, which passes	55 trials, 2,696 patients: more fever than controls, no rise in infection, clots, death or cancer

A trial reports averages from careful protocols. Your own experience depends on the joint treated, the volume injected and your general health, so ask your doctor what to expect for your specific plan. For what the days after treatment look like, see what to expect during treatment and recovery, and for the IV route specifically, our guide to stem cell IV therapy.

Is stem cell treatment safe? Where the serious risks come from

The serious harms in the medical literature cluster around a few situations: unapproved products, unusual injection sites and poor manufacturing. The FDA lists reports of blindness, tumor formation and infections linked to unapproved regenerative products, including fat-derived cells, cord blood, Wharton’s jelly and exosomes (FDA). One well-known case series described three patients who lost vision after a US clinic injected their own fat-derived cells into both eyes (Kuriyan et al., NEJM 2017).

Most of these risks are about process, not biology. That is why the questions to ask a clinic matter more than its marketing. The ISSCR recommends asking what the evidence is for your condition, how the cells are prepared and what happens if something goes wrong (ISSCR guide). Ask us where the cells are processed and for the lab’s INVIMA certification; our page on stem cell therapy legality in Colombia explains what that certification covers.

Can stem cell therapy cause cancer?

In the pooled intravenous trials, mesenchymal stromal cells did not increase the rate of cancer compared with controls (Thompson et al.), although follow-up in most trials is limited. Tumor formation is one of the harms the FDA has received reports about with unapproved products. The theoretical risk is highest with pluripotent cells, which is explained in where stem cells come from and what potency means.

Does stem cell therapy hurt?

A joint injection usually feels like pressure and a deep ache while the fluid goes in, followed by soreness that can be noticeable for some days. If cells are harvested from your own fat or bone marrow, the harvest site adds its own discomfort, and that is often the more painful part. An IV infusion feels like any other IV drip. Your care team will tell you which pain relievers to use: some anti-inflammatory drugs may be avoided around treatment, so ask before taking them.

When surgery or another treatment is the safer choice

The biggest risk of stem cell therapy is often not a side effect but a delay: using an injection when the problem needs a different treatment. Surgery is the better choice for a complete, retracted tendon tear, a joint that gives way from a torn ligament, end-stage arthritis with a collapsed joint, or any spine problem with progressive weakness, numbness or loss of bladder or bowel control. Our comparison of stem cell therapy and surgery for joint pain goes through these cases.

Where stem cell therapy fits

For orthopedic and pain conditions, stem cell therapy is not FDA approved; read what that means for US patients. Reasonable candidates have a clear diagnosis, imaging that shows partial damage rather than complete structural failure, and realistic goals about pain and function. People with an active infection or active cancer are not candidates; see who is not a candidate for stem cell therapy.

Next step

If you want to know whether the risks are worth it in your case, send your records for a free case review. Dr. Catalina Henao reviews your history and imaging, explains the expected side effects of the protocol that would apply to you, and you receive a written quote before you buy flights. Request your free case review.

Frequently asked questions

How long do stem cell injection side effects last?

Soreness and swelling at the injection site are usually short-lived, and fever after an IV infusion passes quickly. Pain that keeps getting worse, a hot red joint or a fever days later are not normal and need a call to your doctor.

Can your body reject stem cells?

Mesenchymal stromal cells are considered to provoke a weak immune response, and pooled intravenous trials did not show more infusion reactions or infections than controls, only more fever. Rejection and graft-versus-host disease are concerns in blood stem cell transplants for cancer, which are a different treatment.

Can you drink alcohol after stem cell therapy?

No studies have tested alcohol and stem cell injections directly. Alcohol can increase bruising and interacts with some pain medicines, so most doctors advise avoiding it around treatment. Follow the written instructions you receive; after a blood stem cell transplant, follow your transplant team.

Is stem cell therapy painful?

A joint injection causes pressure and a deep ache, then soreness for some days. A fat or bone marrow harvest, when used, is usually the more uncomfortable step. An IV infusion feels like a normal IV.

Are Wharton’s jelly stem cell products safe?

The FDA lists Wharton’s jelly among the unapproved regenerative products it has warned consumers about. Its safety depends on how the material is processed and tested, so ask any clinic for the lab’s documentation.

Can stem cell therapy cause cancer?

Trials of intravenous mesenchymal stromal cells have not shown more cancer than controls, but follow-up is limited. The FDA has received reports of tumor formation with unapproved products.

Sources

• US FDA: Important Patient and Consumer Information About Regenerative Medicine Therapies
• ISSCR: A Guide to Stem Cell Treatments
• Thompson M, et al. Intravascular mesenchymal stromal cells continue to appear safe: updated systematic review and meta-analysis. EClinicalMedicine. 2020
• Cao M, et al. Efficacy and safety of mesenchymal stem cells in knee osteoarthritis: meta-analysis of RCTs. Stem Cell Res Ther. 2025
• Han JH, et al. Intra-articular SVF and adipose MSC injections for knee osteoarthritis: meta-analysis of RCTs. Arthroscopy. 2025
• Kuriyan AE, et al. Vision loss after intravitreal injection of autologous “stem cells” for AMD. N Engl J Med. 2017