This article is a collaboration between The New Yorker and ProPublica.

Their shoulders and backs and knees were giving out. Pills and steroid injections hadn’t eased their pain. They were scared of surgery. So, one afternoon last October, two dozen men and women, many of them white-haired, some leaning on canes, shuffled into a meeting room at Robson Ranch, a luxury retirement community in Denton, Texas. Sipping iced tea and clutching brochures that promised a pain-free tomorrow, they checked off their ailments on a questionnaire.

They were there to see a presentation by David Greene, who was introduced as a “retired orthopedic surgeon.” Atlas Medical Center, a local clinic that specializes in pain treatment, hosted the event. Greene, a short, trim man with his hair slicked up, ignored the stage and microphone and stood close to his audience. After warming up the crowd with a joke about his inept golf skills, Greene launched into his sales pitch. A tiny vial no larger than the palm of his hand, he told the group, contains roughly ten million live stem cells, harvested from the placenta, amniotic fluid, umbilical cord, or amnion, the membrane that surrounds the fetus in the womb. Injected into a joint or spine, or delivered intravenously into the bloodstream, Greene told his listeners, those cells could ease whatever ailed them.

On a screen behind him, Greene displayed a densely printed slide with a “small list” of conditions his stem-cell product could treat: arthritis, tendinitis, psoriasis, lupus, hair loss, facial wrinkles, scarring, erectile dysfunction, heart failure, cardiomyopathy, chronic obstructive pulmonary disease, asthma, emphysema, stroke, Alzheimer’s disease, multiple sclerosis, ALS, neuropathy, pelvic pain, diabetes, dry eye, macular degeneration, kidney failure. And that was just a sample. “I need to add a couple more slides,” Greene said with a laugh.

Greene said that amniotic stem cells derive their healing power from an ability to develop into any kind of tissue, but he failed to mention that mainstream science does not support his claims. He also did not disclose that he lost his license to practice medicine in 2009, after surgeries he botched resulted in several deaths. Instead, he offered glowing statistics: amniotic stem cells could help the heart beat better, “on average by twenty per cent,” he said. “Over eighty-five per cent of patients benefit exceptionally from the treatment.”

“Patients come back to the center saying, ‘I can walk farther, I can breathe easier, I can sleep better,’ ” he proclaimed. “It’s remarkable, the outcomes we’ve been seeing for the last few years.” In the second row, a slender woman in a striped jacket, who had hobbled into the meeting on a wooden cane, pumped her fists in the air. “Stem cells!” she cheered.

For more than half a century, the regenerative possibilities of stem cells—which the body stores to repair damaged tissue and organs and restore blood supply—have tantalized the medical community. Bone-marrow transplants for cancer patients, which rely on blood stem cells, fulfill this potential. But alongside legitimate, scientifically proven treatments, an industry has sprung up in which specialized clinics offer miracle remedies from poorly understood stem-cell products.

These clinics are multiplying in the United States. According to a tally by Leigh Turner, an associate professor of bioethics at the University of Minnesota, there were twelve such clinics advertising to consumers in 2009; in 2017, there were more than seven hundred. Unproven cellular therapies are a two-billion-dollar global business, according to a recent paper co-authored by Massimo Dominici, the lead investigator at the cellular therapy lab at the University of Modena and Reggio Emilia, in Italy.

This burgeoning business is largely unregulated. Technically, manufacturers are required to submit stem-cell therapies for review as a drug, and to provide evidence of their safety and efficacy, but the U.S. Food and Drug Administration hasn’t enforced the rule consistently. The former F.D.A. commissioner Scott Gottlieb acknowledged in an interview that the agency’s laissez-faire attitude has made it easier for stem-cell clinics to proliferate. “This is an example where the F.D.A., for a long period of time, took enforcement discretion, then the field grew,” he said. “Then it becomes hard to step in and actually apply the regulation.”

Many clinics offer stem cells taken from a patient’s own bone marrow or fat. But they’re being challenged by a newer technology: amniotic stem cells.

Greene’s company, R3 Stem Cell, was established in 2013. It distributes amniotic stem cells to about thirty clinics nationwide, which have administered them to ten thousand patients, according to an R3 brochure. It also handles marketing for the clinics. In an interview, Greene acknowledged that the benefits of amniotic stem cells that he touted at the Robson Ranch seminar are based on “a lot of success stories,” rather than on clinical trials. “I don’t claim anything,” he added. “I don’t claim that this is a treatment. I don’t claim that it cures anything. I don’t claim that it’s a permanent fix. All I discuss is maybe, potentially, people can get some improvements from stem-cell care.”

One appeal of amniotic stem-cell treatments is convenience. They don’t require patients to undergo liposuction or bone-marrow extraction; instead, manufacturers harvest the cells from tissues donated by women who have recently given birth, and the cells are then frozen and shipped to clinics. There is no special training needed to administer amniotic treatments, either—a nurse practitioner on staff can give injections—so chiropractors, beauticians, and sports-medicine doctors can enter the field with relative ease. A procedure such as an injection into a joint might take about ten minutes and cost between five and ten thousand dollars. For systemic diseases, such as lupus, some clinics also administer the cells intravenously, which can cost more than ten thousand dollars per session.

Because amniotic-stem-cell treatments don’t undergo the clinical trials required for F.D.A. approval, there’s little data or research on them. Their efficacy is highly questionable and, in one case where bacteria contaminated the supply, the lack of accountability in the industry has led to serious infections for a dozen patients. An investigation by ProPublica and The New Yorker found disgraced doctors who were recast as salespeople, manufacturers that cloaked themselves in pseudo-science and had few scientists on staff, and clinics that offer to treat conditions like multiple sclerosis or kidney disease without specialized training. Unscientific methods, deceptive marketing, price gouging, and disregard for patients’ well-being were rampant across the amniotic-stem-cell-therapy industry.

The supply chain for amniotic therapy starts and finishes with people who are at vulnerable times in their lives: the cells come from new mothers, and go to chronically ill patients. Women who undergo cesarean sections are often asked to donate their birth tissue shortly before the procedure. By law, they cannot be compensated for it. Mothers who donated their tissue told ProPublica and The New Yorker that they assumed, or were assured, that it would be used for a worthy cause—and that, otherwise, it would be disposed of as medical waste. But they could not recall the details of the donation process, owing to the haze of childbirth. “Someone walked in with a form while I was in labor and asked if I wanted to donate” the umbilical cord, Julie Menge, who gave birth in Pittsburgh in 2015, said. “I said, ‘Sure!’ And I have no idea what happened to it.”