Stem cell therapy uses the body’s own building-block cells, or lab-prepared versions of them, to repair damaged tissue, replace lost cells, or reset a malfunctioning immune system. The concept is straightforward: stem cells can copy themselves and transform into specialized cell types like heart muscle, blood cells, or nerve cells. By directing that ability toward a specific injury or disease, doctors aim to restore function that the body can’t recover on its own. The reality, though, is more nuanced than the marketing around it suggests.
How Stem Cells Differ From Other Cells
Most cells in your body are specialists. A muscle cell contracts. A nerve cell transmits signals. A red blood cell carries oxygen. None of them can become something else, and most don’t divide to make new copies of themselves. Stem cells break both of those rules. They can self-renew, producing more stem cells, and they can differentiate, turning into the specialized cell types your body needs.
When a stem cell divides, the two resulting daughter cells can go in several directions: both can remain stem cells, both can start specializing, or one of each. This flexibility is what makes them so valuable in medicine. Your body already relies on populations of stem cells tucked inside organs and tissues, quietly waiting in a dormant state until normal wear and tear, injury, or disease signals them to activate and produce replacements.
Three Main Types Used in Medicine
Embryonic stem cells come from the inner cell mass of very early embryos at the blastocyst stage, just a few days after fertilization. These cells are pluripotent, meaning they can give rise to virtually any cell type in the body. That versatility makes them powerful research tools, but their use raises ethical questions because extracting them destroys the embryo.
Adult stem cells exist in tissues throughout your body, including bone marrow, fat, and blood. They’re more limited than embryonic stem cells, typically producing only the cell types found in the tissue where they live. Bone marrow stem cells, for example, generate blood cells. These are the most commonly used stem cells in approved treatments today.
Induced pluripotent stem cells (iPSCs) were first created in 2006 when researchers found a way to reprogram ordinary adult cells back into a stem-cell-like state. iPSCs behave similarly to embryonic stem cells, with the ability to become nearly any cell type, but they’re made from the patient’s own tissue. This sidesteps the embryo debate and, in theory, reduces the risk of immune rejection.
What Actually Happens During Treatment
The specifics depend on the condition being treated, but most stem cell procedures follow a general pattern: harvest, process, deliver.
For bone marrow transplants, the most established form of stem cell therapy, harvesting typically takes about an hour in an operating room under general anesthesia. A thin, hollow needle is inserted through the skin into the back of the hip bone, usually at two to four sites, and the needle goes in multiple times until enough marrow is collected. The harvested material then goes to a lab, where it’s processed, sometimes combined with a preservative, and either frozen for later use or given to the patient the same day. Delivery can be as simple as an intravenous infusion, similar to a blood transfusion.
For orthopedic or joint treatments, the process is different. Cells may be drawn from bone marrow or fat tissue, concentrated, and then injected directly into the problem area, such as a knee or shoulder. These procedures are typically outpatient and far less involved than a full transplant.
Conditions With Proven Treatments
The FDA has approved a narrow set of stem cell products for use in the United States. All of them are blood-forming stem cells derived from umbilical cord blood, and they are approved only for disorders that affect blood production. This includes certain leukemias, lymphomas, and inherited blood disorders like sickle cell disease. In these cases, a stem cell transplant can replace a patient’s diseased bone marrow with healthy cells capable of producing normal blood.
Outside of blood-forming transplants, no other stem cell products currently have FDA approval. That’s a critical distinction, because hundreds of clinics across the country market stem cell injections for joint pain, back injuries, anti-aging, neurological conditions, and more. The gap between what’s approved and what’s advertised is enormous.
The Evidence for Knee Osteoarthritis
Joint pain, especially knee osteoarthritis, is one of the most common reasons people seek out stem cell therapy. A large Cochrane review examined 25 randomized trials involving 1,341 participants and found a modest benefit. Among patients who received a placebo injection, about 53% reported treatment success. Among those who received stem cell injections, roughly 68% did. That’s a real difference, but not a dramatic one.
The review also found that serious adverse events were rare and occurred at similar rates in both groups. So stem cell injections for knee osteoarthritis appear relatively safe in the short term. The problem is confidence in the results. Most trials were small, ranging from 6 to 252 participants, and the source, preparation method, and dose of stem cells varied widely across studies. The researchers rated the overall certainty of the evidence as low to very low, partly because several larger trials were started but never published their results, raising concerns about publication bias. No studies measured whether stem cell injections actually slowed cartilage breakdown on imaging.
Risks and Side Effects
Stem cell therapy is not risk-free. For established transplant procedures, common short-term side effects include nausea, vomiting, fever, and temporary increases in blood pressure. One study of pediatric bone marrow transplant recipients found that 4.9% experienced an adverse event within the first 48 hours of infusion, with high blood pressure being the most frequent.
For unregulated clinic treatments, the risks are harder to quantify because these procedures often happen outside of formal clinical trials. Reported complications from unapproved stem cell treatments have included infections, tumors at injection sites, and loss of vision after eye injections. When cells are minimally processed or used in ways they weren’t designed for, the outcomes are unpredictable.
The International Society for Stem Cell Research has stated clearly that stem cell therapies which involve substantial manipulation of cells, or use cells in ways unrelated to their normal function, must be proven safe and effective through well-controlled clinical trials before being offered to patients. Limited exceptions exist for life-threatening conditions with no other treatment options.
Cost and Insurance Coverage
The cost of stem cell injections for orthopedic or regenerative purposes ranges from roughly $1,300 to $8,500 or more per treatment, depending on the type of cells used, the body part being treated, and the clinic. Most insurance plans do not cover these procedures because they haven’t been FDA-approved for those uses. By contrast, hematopoietic stem cell transplants for blood cancers and related conditions are covered by insurance, though they involve far greater overall costs due to hospitalization, chemotherapy, and extended follow-up.
Gene Editing and Stem Cells Together
One of the most promising frontiers in stem cell science involves combining stem cells with gene-editing tools. Researchers have used gene editing to correct disease-causing mutations in iPSCs before differentiating them into the desired cell type. In Alzheimer’s disease models, for instance, editing a high-risk gene variant in patient-derived stem cells and then growing them into nerve cells significantly reduced the buildup of the toxic proteins associated with the disease. Mice with an Alzheimer’s-like condition showed improved cognitive function after receiving these edited cells.
Similar work is underway in Parkinson’s disease, where edited stem cells engineered to secrete a protective protein reduced nerve cell death and improved motor function in mice. Researchers are also using gene editing to knock out immune-recognition genes in stem cells, creating something closer to “universal” donor cells that the recipient’s immune system is far less likely to attack. In one experiment, editing a single gene in umbilical cord stem cells made them nearly invisible to immune cells, cutting immune cell activation to less than 35% of what it would normally be. These approaches are still in animal models and early human testing, but they represent a meaningful shift from using stem cells as simple replacement parts toward engineering them as precision therapies tailored to individual patients and diseases.