Stem cell treatment uses the body’s own repair cells, or donor cells, to restore damaged tissue, replace diseased blood cells, or reduce inflammation. The specific approach varies widely depending on the condition being treated. Some stem cell therapies are well established with decades of clinical data, while others are still experimental, and a growing number of unregulated clinics offer treatments with little evidence behind them.
How Stem Cells Work in the Body
Stem cells were originally thought to help mainly by transforming into whatever cell type was needed, essentially filling in for dead or damaged tissue. That does happen, but research has shown it plays a smaller role than expected. When stem cells are injected into an injury site, relatively few of them actually survive and integrate into the tissue long-term. The percentage that engraft is low and decreases over time.
The bigger contribution comes from what stem cells release. They secrete a range of chemical signals that act on the surrounding tissue, a process called paracrine signaling. These signals attract immune cells, stimulate the growth of new blood vessels, recruit skin and connective tissue cells to the area, and speed up cell division in the tissue that’s already there. In wound-healing studies, even the liquid that stem cells had been sitting in (with no actual cells present) accelerated tissue repair. This strongly suggests the molecules stem cells release matter as much as, or more than, the cells themselves.
Blood Cancer and Bone Marrow Transplants
The oldest and most proven form of stem cell treatment is the bone marrow transplant, now more commonly called a hematopoietic cell transplant. It’s a standard treatment for children and adults with high-risk leukemia, lymphoma, and other blood disorders. The basic idea: destroy the patient’s diseased bone marrow with chemotherapy or radiation, then replace it with healthy blood-forming stem cells from a donor or from the patient’s own stored cells.
Outcomes have improved dramatically. In pediatric leukemia, five-year survival rates for transplant patients with very high-risk disease reached 65% for acute lymphoblastic leukemia and 74% for acute myeloid leukemia in recent treatment protocols. Earlier approaches produced five-year survival rates closer to 28% and 34%, respectively. The transplanted cells are infused through an IV line over one to several hours. Engraftment, when the new cells begin producing healthy blood cells, typically takes about 30 days. The first 100 days after transplant are the highest-risk period, with close monitoring for infections and complications. Many patients leave the hospital during this window and shift to outpatient care.
Autologous vs. Donor Cells
When your own cells are harvested, stored, and returned to you, that’s called an autologous transplant. When cells come from another person, it’s an allogeneic transplant. The distinction matters because of immune rejection. Your body won’t attack its own cells, but donor cells can trigger a serious condition called graft-versus-host disease, where the transplanted immune cells treat your body as foreign and attack healthy tissue. In studies of allogeneic transplants for blood cancers, moderate to severe acute graft-versus-host disease occurred in about 31% of patients, and chronic graft-versus-host disease developed in 42%.
Despite this risk, donor transplants have a unique advantage for cancer treatment. The transplanted immune cells can recognize and attack remaining cancer cells, an effect that autologous transplants can’t provide.
Knee and Joint Injections
One of the most common reasons people encounter stem cell therapy today is for joint pain, particularly knee osteoarthritis. Clinics offer injections of mesenchymal stem cells (a type found in bone marrow and fat tissue) directly into damaged joints. A large meta-analysis of clinical trials found that patients receiving these injections had significantly greater pain reduction compared to controls, with the strongest effects showing up at 24-month follow-up. Functional scores measuring stiffness, pain, and physical ability also improved meaningfully.
These results are encouraging, but the treatments remain largely experimental. The FDA has not approved mesenchymal stem cell injections for osteoarthritis, and most insurance plans do not cover them. Out-of-pocket costs for knee injections typically run between $5,000 and $10,000, with back and shoulder procedures ranging from $5,000 to $15,000. The average across all stem cell procedures sits around $10,000, though many patients pay well over $20,000.
Heart Failure Results Are Mixed
Researchers have spent over a decade testing whether stem cells can improve heart function after heart failure, specifically whether they can increase the heart’s pumping efficiency (measured as ejection fraction). The results so far are inconsistent. A review of multiple clinical trials found that both muscle-derived and bone marrow-derived stem cells showed mixed results. Most studies found no statistically significant improvement in heart function at follow-up compared to placebo groups. A few smaller studies showed modest gains: one found improvement in about half of patients at five years, and another showed significant early improvement at three months that was maintained at one year. But these positive findings were not replicated in larger, controlled trials.
Heart failure remains an active area of stem cell research, but the therapy is not part of standard cardiac care.
Neurological Conditions
Parkinson’s disease is one of the most closely watched targets for stem cell therapy. The disease destroys dopamine-producing neurons in the brain, leading to tremors, stiffness, and difficulty with movement. Early-stage human trials have shown that stem-cell-derived neurons can be injected into the brain safely and that the transplanted cells survive long enough to produce dopamine. Some participants experienced visible reductions in tremors. These are preliminary results from small trials, but they represent a meaningful step toward replacing the exact cells lost to the disease rather than just managing symptoms with medication.
What the FDA Has Actually Approved
The list of FDA-approved stem cell products is much shorter than most people expect. The bulk of approvals are for cord blood products, which contain blood-forming stem cells used to treat blood cancers and certain immune disorders, the same category as traditional bone marrow transplants. Beyond that, the FDA has approved a handful of cell-based products for specific uses: cultured cartilage cells on a collagen scaffold for repairing knee cartilage defects, and engineered skin substitutes made from cultured skin cells for wound treatment.
That’s essentially it. The vast majority of stem cell treatments advertised by clinics for conditions like back pain, anti-aging, erectile dysfunction, autism, or lung disease are not FDA-approved and have not been proven effective in controlled trials.
Risks of Unproven Treatments
The FDA has documented serious complications from unapproved stem cell products, including blindness, tumor formation, life-threatening blood infections, and neurological events. The specific risks include cells migrating to unintended parts of the body and growing into the wrong type of tissue, immune reactions against the injected cells, bacterial or viral contamination from improper processing, and treatments simply failing to work while the patient delays proven therapies.
The tumor risk deserves particular attention. Stem cells’ ability to multiply and transform into different cell types is exactly what makes them therapeutically interesting, but it’s also what makes them dangerous when poorly controlled. Cells injected into one location can travel elsewhere and grow in ways that weren’t intended. This is a fundamentally different risk profile than a conventional drug that gets metabolized and leaves the body.
If you’re considering a stem cell procedure, the clearest safety signal is whether the treatment is part of a registered clinical trial or uses an FDA-approved product. Clinics that promise results for a wide range of unrelated conditions, charge large upfront fees, and aren’t conducting formal research are the ones most likely to cause harm.