Yves here. Yours truly has had more than a little experience with diet, dietary supplement, and alternative medicine fads. When the peptide buzz started a few years ago, I paid little attention because the promised benefits were in “too good to be true” terrain.
This article gives even more cause for pause. Snake-oil-salesman-in-chief, RFK, Jr, is throwing his weight behind a peptide, BPC-157, developed by a medical researcher who makes miracle claims for its benefits with virtually no evidence to back it up. Worse, the research was conducted in Zagreb, Croatia, starting in the 1970s. I visited Zagreb in 1997. Absolutely no way would I consider anything in the medical category out of Zagreb based on what I saw then. Not only was it clearly markedly behind the West pretty much across the board, but the quality standards in the supposedly top-drawer hotel I used and the restaurant where I was taken were poor. By contrast, in 2000, I had a flare up of an orthopedic issue when I was in Bangkok. The hospital I went to was spartan-looking but very clean and the doctor gave me a very good exam and an effective treatment. So my view about Zagreb does not reflect a prejudice against outside-the-first-world institutions.
In 1975, in a medical school classroom in what was then the Socialist Federal Republic of Yugoslavia, Predrag Sikiric had an idea that he has pursued for more than 50 years.
His obsessive quest would take him from gastroenterology clinics to international scientific conferences, define his career as an academic, and capture the attention of global pharmaceutical companies. It would eventually become one part of the Make America Healthy Again movement’s effort to reform federal drug regulation.
This story is being co-published with STAT News, and was supported by the Pulitzer Center.
But at the time, Sikiric was just a second-year medical student at the University of Zagreb School of Medicine in Croatia, listening to a lecture about the adrenal glands and the body’s response to stress. Overwhelming stress, he knew, could damage the lining of the stomach. Surely, he thought, the stomach itself must produce a substance that allows the body to fight back — a sort of anti-stress chemical. It would be natural and free of side effects, he imagined. If someone could find it, they would have their hands on a remarkable medication.
The idea was lofty. To many scientists, he acknowledges, it still sounds impossible. Yet eight years later, at the outset of his Ph.D., Sikiric managed to inspire a small band of colleagues to join him in the search for this hypothetical compound, which he dubbed Substancija Boze Pomozi, or, roughly, “substance God help me.”
First, they needed gastric juice. A lot of gastric juice. Sikiric said he and his team collected the highly acidic stomach fluid from gastroenterology clinics and emergency rooms, where it was a waste product of some medical procedures. As part of the search, he said, he often traveled to a hospital in the seaside city of Split, where he obtained the juice in bottles and plastic bags. A physician friend in Bosnia and Herzegovina sent near-daily shipments by bus. Some team members visited pig slaughterhouses, where the GI tract is typically removed from the meat to prevent contamination. Sikiric remembers the juice sometimes harbored rats that had been caught and eaten by the pigs in their final hours.
They brought it all back to the University of Zagreb and stored it in a communal refrigerator in the Department of Pharmacology. Occasionally a glass bottle would crack and emit a rancid smell. But Sikiric had the unwavering support, he recalls, of the department leader, so he pressed ahead.
The group spent years subjecting the gastric juice to a special kind of screening process. The details are proprietary, Sikiric said, and he declined to share them. But, in interviews, he and a colleague described the general process. The team’s chemists would isolate compounds from the juice, and then Sikiric would test those compounds using animal experiments. He repeated this procedure many times, homing in on what he wanted.
Sikiric said that in 1989, they found what they were looking for: a substance that seemed to possess a wide range of healing effects to help the body return to normal after it was subjected to stress. That substance was a protein, and from it, they identified a smaller substance that they believed was the active principle, or the part of the protein responsible for producing the therapeutic benefits.
This piece of protein, a type of molecule called a peptide, was just 15 amino acids long. Sikiric dubbed it “BPC 157.” In time, it became a kind of bootleg panacea, sold by gray-market vendors to bodybuilders and biohackers, even as it struggled to win the approval of mainstream medicine.
Today, Sikiric and his team describe BPC-157 as an all-purpose healing compound. Laboratory experiments with animals and cell cultures, they write, suggest the peptide may treat everything from muscle injuries to glaucoma to ulcers. And few if any side effects have been documented in the scientific literature.
Still, where some see a promising drug, others see big claims backed by little evidence. Many medical researchers warn that there’s scant published data showing whether — or how — the peptide actually works in human beings. Some have also raised pointed questions about whether BPC-157 originates in the human body at all. Sikiric’s team, they say, may have made an honest mistake all those years ago, accidentally yielding a sequence of amino acids that’s not actually produced in the body
In Sikiric’s office, a jar with the label “BPC” sits on a shelf.Visual: Sara Talpos for Undark
Now the peptide is at the heart of a polarized debate in the United States, one that raises a core question about how the Food and Drug Administration ought to regulate drugs: Should regular Americans be able to access unapproved substances like BPC-157? Since 1962, in order to bring a drug to market, manufacturers have been required to run controlled trials in human beings to gauge safety and effectiveness. That vetting has not happened for Sikiric’s peptide, and federal regulation technically restricts its sale.
Health and Human Services Secretary Robert F. Kennedy Jr., however, has said that it’s not the FDA’s role to prevent people from accessing experimental medicine. Instead, he says, Americans should be able to decide for themselves whether to try an unapproved therapy. When it comes to unapproved peptides like BPC-157, he has made an additional argument: These substances are already on the gray market, raising the risk that someone may be harmed by a mislabeled or contaminated product. It would be safer to allow people to get these unapproved medications from a licensed pharmacy, Kennedy has argued.
This summer, an FDA advisory committee will consider allowing pharmacies to compound and sell seven unapproved peptides, including BPC-157. In an April post on X, Kennedy wrote that for each peptide, the committee will weigh the “full clinical, pharmacological, and safety evidence.” The next day, he asserted that these peptides are like supplements, and therefore might not need to go through clinical trials.
“This is a brave new world,” said Jacob Sherkow, a professor of law and medicine at the University of Illinois. For decades, the FDA has treated injectable peptides, like insulin, as drugs. Now, with this potential pivot, the approach is more “‘You know, we’re going to allow some of these to go forward without any rigorous scientific evidence base,’” he said.
In the case of BPC-157, the majority of evidence comes out of Sikiric’s lab in Zagreb. But the full history of the peptide’s development has not been written — in part because Sikiric has never published some details about the discovery and human testing of BPC-157, and in part because he has rarely chosen to go on-the-record with English-language reporters.
In May, though, he granted Undark access to his team at the University of Zagreb School of Medicine, including extensive interviews with him, his collaborators, and more than 20 current and former Ph.D. students, most of whom continue to work on BPC-157. Many of these interviews took place in Sikiric’s office, which is lined with houseplants, a Croatian flag, and photographs of Sikiric with colleagues. In 2020, an earthquake damaged the building that houses his main laboratory, so boxes and lab equipment were piled up in the office’s corners.
During the visit, Sikiric was demonstrably concerned that the story of his decades-long project, which is now embedded in a moment of reckoning for drug regulation on the other side of the globe, be told as he sees it. He often turned to his PowerPoint presentations to explain the science. On a beautiful Saturday afternoon, while Zagreb was full of people turning out for Europe Day celebrations, Sikiric sat down in his office.
“So, we are here,” he said, pointing to a slide. “You have to be sure that you get it.”
Sikiric, who is now 72, still works full days, typically without taking a break to eat. His colleagues and students describe him as hyper-focused, emotional, and not particularly interested in status or titles. “He didn’t play that conventional academic game of ‘respect hierarchy,’” recalled one of his former Ph.D. students. “He was just like ‘that’s bullshit — and let’s do the work.’”
Sikiric grew up in Zagreb, the oldest of four children, on a street lined with apartment homes dating back to the Austro-Hungarian Empire. His father, he said, was a prominent attorney who specialized in patent issues, and an outspoken critic of the Communist party who narrowly escaped execution after World War II. He was often put in jail, Sikiric recalls, including whenever the Yugoslav President, Josip Broz Tito, came to Zagreb. Sikiric took to calling this “free local accommodation.”
When Sikiric entered medical school in the 1970s, he recalled, some lecture materials were only available on the black market. He asked the professors to write out the class content, and then he helped organize a group of students who printed the material with a hand-cranked machine. Later, as a young doctor, Sikiric worked in rural areas of the country, where he sometimes had to ration medical equipment and personnel.
In the 1980s, when the work on gastric juices began, funding for Croatian scientists was limited, Sikiric said, and there were few opportunities to engage with Western researchers. Towards the end of that decade, Sikiric published several papers based on his Ph.D. research in a European pharmacology journal. That work came across the desk of a professor who was then at Harvard, Sandor Szabo, who sent Sikiric a letter inviting him to a scientific conference in Canada held in 1989.
The experience opened Sikiric up to a world of researchers interested in the body’s response to stress. In 1936, endocrinologist Hans Selye had published a landmark paper in Nature, describing how many different harms — toxins, injury, and cold temperature — can trigger the same biological stress response. Some 40 years later, his former student, a researcher named André Robert, showed that hormone-like substances called prostaglandins could protect the stomach lining from injury. He called that process cytoprotection. Szabo, another former Selye student, built on those findings to show that cytoprotective compounds work, in part, by protecting the blood vessels just beneath the stomach lining. This helps maintain circulation, which in turn leads to less tissue damage and faster healing.
Sikiric believed that BPC-157 was cytoprotective, too. He took the concept one step further: Instead of locating cytoprotection primarily in the stomach, or in the GI tract, he theorized that the peptide could preserve blood vessels — and thus protect tissue — across every organ of the body.
It was a promising time to build international collaborations. Walls were falling across Eastern Europe. A sense of freedom was in the air, Sikiric recalls. But for Croatia, it was clear there would be no independence without war.
In the years leading up to the collapse of Yugoslavia, Sikiric had changed the name of the substance to BPC, an acronym that carried two meanings at once: Bože Pomozi Croatia, “God Help Croatia,” and, in the scientific literature, “Body Protection Compound.” Eventually, they added 157 to the name of the peptide, as Sikiric said that July 15, 1990 had been rumored — wrongly, it turned out — to be the date when the country was going to declare independence.
When the declaration came the following summer, war broke out between the young state and Serbian-controlled forces opposed to Croatian independence. Many medical school faculty members were engaged in the war in some way, recalled Sven Seiwerth, a pathology professor at the university who has worked on the BPC-157 project since the 1980s. He volunteered to work as a medical doctor on the front lines. At the time, he had a wife and two young children. “It was just a matter of surviving,” he said.
In 1992, other nations began to recognize Croatia as an independent state, and inside the country, political winds were finally at the team’s back, Sikiric said. He had one big stroke of luck: Zagreb was home to a major pharmaceutical company, PLIVA, which was enjoying a windfall from developing the antibiotic azithromycin.
The company was looking for its next blockbuster. In 1993, Sikiric said, he signed a contract with PLIVA. The company began researching BPC-157, working alongside university researchers and an American pharmaceutical company called Parke-Davis.
They got some promising results. In a study from 1995, for example, researchers at a Parke-Davis facility in Ann Arbor, Michigan, administered the substance to rats and found that it helped protect the rodents’ colons from harsh chemicals administered into their intestines an hour later. Studies by a team of researchers at PLIVA and the University of Pécs in Hungary found a similar protective effect when they tested pieces of the peptide in freshly isolated rat stomach cells.
PLIVA also began testing the drug in humans. In the early 2000s, the company held two early-stage trials to see if BPC-157 could help treat ulcerative colitis. Researchers never published the full results, although a short write-up in 2005 reported that the second trial found a positive effect but that it didn’t reach statistical significance.
Accounts differ as to what happened next. According to Sikiric, PLIVA scientists were ready to move forward with a Phase 3 trial, in addition to new trials to test the effect of the peptide on wound healing. But in 2006, the company’s research institute was sold to GlaxoSmithKline. Meanwhile, the rest of PLIVA, which was focused on generic drugs, was acquired by Barr Pharmaceuticals that same year. Barr was then acquired by Teva Pharmaceuticals in 2008.
The BPC-157 project was transferred to GSK, but the company dropped it. That’s not because the drug didn’t work or was found to be unsafe, Sikiric said, but because the people at GSK were wedded to their own projects. He believes GSK abandoned a promising drug.
“When a big company takes over a little company, they pick out the bits that they think fit what they want, and leave the rest,” said Michael Parnham, who was a senior scientific adviser at PLIVA at the time of the acquisition by GSK.
Parnham was recruited to PLIVA in 1998, and he said he was skeptical of the BPC-157 project from the get-go. For one thing, it came with an unusual licensing agreement in which PLIVA had agreed to bring the drug to clinical trials, he said. (Sikiric says the agreement was to take it all the way to market, though he declined to show the agreement to Undark.)
Parnham also found the experimental results underwhelming. At PLIVA, his team published two papers comparing BPC-157’s ability to heal wounds in rats against the standard therapy. BPC-157, they observed, promoted the early development of granulation tissue, which is made up of cells and new blood vessels that support repair. They wrote that the peptide seemed to stimulate, either directly or indirectly, a specific gene involved in the body’s response to injury.
But it barely outperformed an existing drug. “In the hard world of drug marketing and drug sales, it would have been extremely difficult to convince people, ‘Look, we’ve got something better,’” Parnham said.
Parnham also expressed hesitation about the way Sikiric presented the data, describing him as wielding flashy slides with too much certainty, “like a marketing pitch.”
At the end of 2009, the licensing rights to BPC-157 were returned to Sikiric, along with all of the data that PLIVA had generated. He and his team have continued to research the peptide on their own, mostly doing studies in rodents. A handful of other teams — including in Taiwan, South Korea, China, and Turkey — have also published studies, all reporting positive results and documenting few, if any, side effects.
Not everyone sees the lack of side effects as a positive: “Anything without side effects is probably not very active,” said Parnham. And there still isn’t much in the way of human data. A clinical trial, begun in Tijuana around 2015 and sponsored by a Croatian company that lists Sikiric as a partial owner, is listed as canceled in a U.S. government database. In a 2025 review, Sikiric and his team report that the study found the peptide was “safe and well-tolerated,” but they have not published the data.
A generation ago, the story might have ended there. But according to Luke Turnock, a criminologist in the U.K., around 2010, in online forums, bodybuilders began talking about peptides, and some seem to have found their way to Sikiric’s scientific papers. These gym-goers, Turnock said, figured out how to source peptides like BPC-157 from suppliers in China. Soon, a thriving gray market emerged, with BPC-157 as one of its stars.
Sikiric can’t remember exactly when he first learned that bodybuilders were using BPC-157. But he does recall what he felt: happiness, like a parent watching their child grow up and come into its own.
“What is the essential purpose of the drug?” he asked. “To be useful for the people.”
BPC-157’s use has since spread from bodybuilders to biohackers to patients with unmet medical needs. It’s now widely sold online, often marketed as a natural substance, produced by the human body, that has been spurned by pharmaceutical companies but discovered by medical outsiders.
It has also been picked up by the MAHA movement. On an episode of his “Ultimate Human Podcast” this past December, Gary Brecka, a wellness entrepreneur and a key figure in the MAHA movement, ticked off a half dozen diseases and conditions that he believes BPC-157 can treat. It and other unapproved peptides, he suggested to his guest, then-FDA commissioner Marty Makary, have produced “astounding results.”
On an afternoon in March, Anna Mapp sat down at a table in her office with a loose pile of printouts. At the request of Undark, the University of Michigan chemist — and current president of the American Peptide Society — had reviewed several BPC-157-related documents, including the Croatian team’s patent for isolating BPC-157’s parent protein.
Sitting across from large papier-mâché molecules made by former students, Mapp expressed surprise at the limited amount of detail in the patent. Even the protein’s molecular weight isn’t pinned down. “There was no demonstration that I could tell that it was a single pure isolated substance,” said Mapp. Had the team isolated just one protein, or a mixture of different substances?
It’s also unusual that the full protein’s sequence was never published, she said, describing the omission as unacceptable under today’s standards of scientific practice. Without the full sequence, it’s impossible to reproduce the original work, a crucial form of quality-control for scientists.
And as for the peptide itself, genetic material that codes for its unique amino acid sequence hasn’t been found in the human genome or gut microbiome. “That is troubling,” said Mapp.
It’s also not clear how the peptide would act on the body, she noted — a point raised by several other researchers. “The vast majority of peptides require receptors to work,” Patricia Brubaker, a peptide scientist at the University of Toronto, wrote in an email to Undark. Most peptide drugs work by binding to a receptor on the surface of cells, a process that then initiates changes in how the cell behaves. But it appears that nobody has definitively found a dedicated BPC-157 receptor, and Sikiric hasn’t focused his research on finding one.
Anna Mapp, a chemist at the University of Michigan and current president of the American Peptide Society, reviewed several BPC-157-related documents at Undark’s request. Mapp said it is unusual that the full protein’s sequence has never been published, and she questioned whether it’s actually produced by the body at all.
All of that evidence, taken together, has led Mapp and other researchers to question a key detail of BPC-157’s origin story: They’re not convinced it’s actually produced by the body at all.
Sandor Szabo, Sikiric’s longtime colleague, co-authored a 2017 paper that presents BPC-157 as a promising drug for the prevention and treatment of ulcers. The paper, at the same time, outlines the missing details that one would expect for a natural substance. If the peptide were made in the body, Szabo and his colleagues wrote, one would expect that over the course of decades, researchers would have identified the gene that encodes it, the cells that make it, the receptors that it interacts with, and the levels at which it occurs in the body.
Perhaps, he says now, the original team misinterpreted an amino acid sequence many years ago. At the time, techniques for performing chemical analyses were not well-refined.
Still, Szabo said he has no doubt that the substance can protect the stomach and small intestine. He pointed back to the several groups, including his own, that have reproduced the findings in cell cultures and rodents.
It may not be a natural compound, he said. “As long as it works and has no side effects, who cares?”
One evening, after most faculty had left the building, Sikiric was still at his computer. On a wall to his right was a print of the Virgin Mary, her face partially obscured by empty lab supply boxes. Beside them, the red-tiled rooftops of Zagreb were visible through a window.
Sikiric clicked through a few slides until he reached one containing a passage about cytoprotection, from a 1979 paperby Robert, the researcher who helped birth the field. It’s a paper that has become a north star for Sikiric’s work, and he invoked it now to defend his project: The passage does not mention receptors, Sikiric pointed out, suggesting to him that Robert didn’t view them as essential for cytoprotection.
Over the past seven months, in dozens of conversations with Undark, Sikiric has laid out his view of how BPC-157 functions inside the body. His research, he says, indicates that the peptide works, in part, by reversing damage to blood vessels and by helping regulate levels of nitric oxide, a molecule that relaxes blood vessels and helps prevent high blood pressure.
Predrag Sikiric and Sven Seiwerth sit in the pathology building of the University of Zagreb in May 2026. The pair have collaborated on the BPC-157 project for more than 40 years. They estimate that 100 or more current and former Ph.D. students have worked with them. Visual: Igor Nobilo for Undark
As Sikiric tells it, there is no other substance right now that compares with BPC-157. He says the peptide promotes blood clotting when that’s what’s needed — and blood thinning when necessary. It can stimulate the creation of new blood vessels when the body needs them to heal from injury, but it doesn’t create new blood vessels that would stimulate tumor growth. (Sikiric disagrees vigorously with researchers who say it’s plausible the peptide could cause cancer.)
He also rejects the idea that the BPC-157 isn’t natural. In an emailed response, he pointed to a number of papers, including research from Taiwan showing indirect effects of BPC-157 on two receptors that promote healing in the body. And he pointed to images from his lab that show BPC-157 in human fetal tissue cells. (At least one researcher was underwhelmed by these images: “I honestly do not find these data convincing in any way,” wrote Brubaker, who noted that she uses this laboratory technique — called immunostaining — in her own research.)
As for why the early patent is scant on details: People can take it up with the U.S. patent office, he said. (This approach isn’t unusual, said Sherkow, the University of Illinois professor: “People put vague stuff in patent specifications all the time.”)
And what about publishing the amino acid sequence of the parent protein, so others can see it? If you have your own child, Sikiric said, you want it to be yours forever.
Besides, he said, the beneficial effects speak for themselves.
He and Seiwerth estimate that between them they have 100 or more current and former Ph.D. students, many of them are now medical school professors and active members of their research team. Again and again, in tissue samples and rodent models, the studies report that BPC-157 works and causes few, if any, side effects.
For a sizable group of Americans, that’s enough. Some have read the studies themselves and don’t want to wait for permission from the FDA; some have heard glowing testimonies about BPC-157 from athletes and popular podcasters. Many say they struggle with chronic conditions and feel poorly served by the medical system, and they often view the FDA as paternalistic and beholden to the profit-driven pharmaceutical industry.
Those sentiments have found a champion in Kennedy, who has embraced experimental therapies as part of his broader skepticism of the medical establishment.
But others think that, for all its flaws, the FDA’s drug approval system is among the best in the world. “I understand why some in the MAHA movement are frustrated with the FDA. And I get that,” said Christopher Mendias, a rehabilitation clinician-scientist at Performance Medicine Institute in Phoenix, Arizona. But all too often, drugs that show promise in experimental animals simply don’t perform very well once they’re tested in humans. The FDA’s current approval system helps ensure that drugs are safe, and that they work, he said. “When we go around that, there’s potential consequences.”
More data on BPC-157 may be coming. Christopher Robinson, a regenerative medicine and pain physician at the Johns Hopkins University School of Medicine, told Undark that he’s applying for funding to run clinical trials testing BPC-157 and other peptides as treatments for chronic pain. He’s applying to the Advanced Research Projects Agency for Health, or ARPA-H, a government agency specifically dedicated to funding high-risk, high-reward research that could transform health care — or fail entirely.
For now, he said, people should “proceed cautiously” if considering taking an unapproved peptide. “I’m coming from the side of scientists where I need data,” he said. “I need legitimate data in order for me to make a decision. I don’t want to give patients something that hasn’t been proven or studied significantly.” Other experts go further; one physician told Undark earlier this year that without actual robust data from clinical trials, BPC-157 “should not be used by humans.”
In Croatia, Sikiric has begun to field more calls from reporters. And he continues to work with his current and former students. In interviews, several of them said they’d welcome clinical trials. This whole project started decades ago, one of them noted, and BPC-157 is like Sikiric’s long-gestating child: “He needs to deliver it.”
