Yves here. I’ve navigated the world of diets, dietary supplements, and alternative medicine fads extensively. Initially, I dismissed the hype surrounding peptides a few years back, since the claims seemed almost too good to be true.
This article raises further questions. Prominent figure RFK Jr. is backing a peptide known as BPC-157, created by a medical researcher making extraordinary claims about its benefits, yet lacking substantial evidence. Compounding the issue, this research began in Zagreb, Croatia, in the 1970s. I visited Zagreb in 1997, and based on my observations then, I wouldn’t trust anything medical from there. The city appeared significantly behind the West in various aspects, and even the quality of service in a reputed hotel and restaurant left much to be desired. In contrast, during a visit to Bangkok in 2000, a hospital, though modest in appearance, was exceptionally clean, and the doctor provided a thorough examination and effective treatment. Thus, my stance on Zagreb does not stem from a bias against non-Western medical institutions.
A Vision Born in the Classroom
In 1975, inside a medical classroom in what was formerly the Socialist Federal Republic of Yugoslavia, Predrag Sikiric conceived an idea that he would pursue for over fifty years.
His relentless quest would transport him from gastroenterology clinics to international scientific forums, shaping both his career as an academic and attracting the interest of global pharmaceutical companies. This endeavor even found its way into the broader movement aimed at reforming federal drug regulations in the U.S.
This story is jointly published with STAT News and was supported by the Pulitzer Center.
At that time, however, Sikiric was merely a second-year medical student at the University of Zagreb School of Medicine, intently listening to a lecture about the adrenal glands and the body’s reaction to stress. He understood that extreme stress might harm the stomach lining. Surely, there must be a natural substance produced by the stomach that enables the body to combat this stress — a kind of anti-stress chemical without side effects. He believed that discovering such a compound could lead to a remarkable medication.
From Concept to Compounds
The idea was grand, and to many scientists, it probably still sounds implausible. Nevertheless, eight years later, just before embarking on his Ph.D., Sikiric managed to rally a handful of colleagues to help him pursue this elusive compound, which he named Substancija Boze Pomozi, roughly translating to “substance God help me.”
Their first step involved gathering ample gastric juice. Sikiric recounted how he and his team collected this highly acidic fluid from gastroenterology clinics and emergency rooms, where it was often a waste product. He frequently traveled to a hospital in Split, where he collected the juice in bottles and plastic bags. A medical colleague in Bosnia and Herzegovina sent daily shipments by bus, and some team members explored pig slaughterhouses, where they retrieved the gastrointestinal tract, taking care to avoid contamination. Sikiric recalls instances where the gastric juice contained remnants of rats that had been eaten by the pigs just before slaughter.
Back at the University of Zagreb, they stored their findings in a communal refrigerator within the Department of Pharmacology. Occasionally, a glass bottle would break, creating a foul odor. Nevertheless, with the unwavering support of the department’s leader, Sikiric pushed forward.
The group spent years applying a unique screening process to the gastric juice. The specific details of this method are proprietary, so Sikiric was tight-lipped about it. However, in interviews, he and a colleague outlined the general approach: chemists would isolate compounds from the juice, which Sikiric would then test in animal experiments. This process was repeated numerous times as they refined their search.
By 1989, they discovered a substance that appeared to possess a diverse range of healing properties that aided the body in recovering from stress. This substance turned out to be a protein, which they believed contained an active component responsible for the therapeutic effects.
This segment of protein, a peptide, was just 15 amino acids in length, and Sikiric aptly named it “BPC 157.” Over time, it garnered a reputation as a kind of underground miracle cure, sold on the gray market to bodybuilders and biohackers, while struggling to gain acceptance in mainstream medicine.
In Sikiric’s office, a jar labeled “BPC” rests on a shelf.Visual: Sara Talpos for Undark
A Polarized Debate
The peptide is now at the center of a contentious debate in the U.S., raising a fundamental question about how the Food and Drug Administration (FDA) should regulate drugs: Should ordinary Americans have access to unapproved substances like BPC-157? Since 1962, drug manufacturers must conduct controlled trials with human participants to assess safety and efficacy before entering the market. This rigorous vetting hasn’t been applied to Sikiric’s peptide, and federal regulations technically restrict its sale.
Health and Human Services Secretary Robert F. Kennedy Jr. has stated that the FDA shouldn’t prevent individuals from accessing experimental treatments. He believes Americans should have the autonomy to decide for themselves whether to pursue unapproved therapies. Furthermore, Kennedy has pointed out that these unapproved peptides are already available in a gray market, increasing the likelihood of individuals being exposed to mislabeled or contaminated products. Hence, he argues that it would be safer for people to obtain these unapproved medications from licensed pharmacies.
This summer, an FDA advisory committee will evaluate whether pharmacies should be allowed to compound and sell seven unapproved peptides, including BPC-157. In an April post on X, Kennedy wrote that the committee will review the “full clinical, pharmacological, and safety evidence” for each peptide. The next day, he asserted that since these peptides are akin to supplements, they might not require formal clinical trials.
“This is a brave new world,” remarked Jacob Sherkow, a law and medicine professor at the University of Illinois. For decades, the FDA has classified injectable peptides, like insulin, as drugs. However, if this new direction takes root, it signals a shift towards a softer stance, where some peptides are permitted entry without robust scientific evidence, he noted.
Although the majority of evidence for BPC-157 stems from Sikiric’s lab in Zagreb, the full account of the peptide’s development remains unwritten. This is partly because Sikiric has not published several critical details about its discovery and human trials, and he rarely engages with English-speaking reporters.
A Deep Dive into the Research
In May, Sikiric granted Undark an opportunity to explore research at the University of Zagreb School of Medicine, conducting in-depth interviews with him, his collaborators, and over 20 current and former Ph.D. students — many of whom are still involved in BPC-157 research. These interviews took place in Sikiric’s office, adorned with houseplants, a Croatian flag, and photographs of him with colleagues. An earthquake had damaged the building housing his main lab in 2020, leading to boxes and equipment cluttering the corners of his office.
During the visit, Sikiric seemed keen for the narrative of his lengthy project, which now intersects with the growing scrutiny of global drug regulations, to be conveyed accurately. He often relied on PowerPoint presentations to clarify scientific concepts. On a delightful Saturday afternoon, while people in Zagreb celebrated Europe Day, Sikiric focused intently in his office.
“So, we are here,” he said, indicating a slide. “You must ensure you grasp it.”
At 72, Sikiric still dedicates long hours to his work, often bypassing meal breaks. His colleagues and students describe him as intensely focused, passionate, and generally uninterested in conventional hierarchies. “He disregarded the traditional academic hierarchy,” recounted a former Ph.D. student. “He’d say, ‘that’s nonsense — let’s focus on the work.’”
Raised in Zagreb as the eldest of four siblings, Sikiric lived on a street lined with buildings dating back to the Austro-Hungarian Empire. His father was a notable lawyer specializing in patent law and a vocal critic of the Communist regime, narrowly escaping execution after World War II. He often found himself imprisoned, Sikiric recalls, particularly during visits from the Yugoslav President, Josip Broz Tito. Sikiric humorously referred to this as his “free local accommodation.”
When Sikiric enrolled in medical school during the 1970s, some lecture materials were only available on the black market. He asked professors for written content, then organized a group to print the materials using a hand-cranked machine. Later, as a young doctor, he worked in rural Croatian communities, where he sometimes had to ration both medical supplies and personnel.
In the 1980s, as work on gastric juices began, funding for Croatian scientists was scarce, with few chances to collaborate with researchers from the West. Towards the end of that decade, Sikiric published several papers based on his Ph.D. work in a European pharmacology journal. This caught the attention of a Harvard professor named Sandor Szabo, who invited Sikiric to attend a scientific conference in Canada in 1989.
This experience opened the door to a network of researchers interested in the body’s stress responses. In 1936, endocrinologist Hans Selye had published a seminal paper in Nature detailing how various forms of harm — toxins, injury, and cold — can trigger similar biological stress responses. Nearly four decades later, his former student André Robert demonstrated that hormone-like substances called prostaglandins could protect the stomach lining from damage, coining the term cytoprotection. Szabo, another protégé of Selye, expanded on these findings to illustrate that cytoprotective compounds safeguard the blood vessels beneath the stomach lining, enabling better circulation and consequently, faster healing.
Sikiric theorized that BPC-157 held cytoprotective properties as well. He proposed taking it a step further: Rather than confining cytoprotection to the stomach or gastrointestinal tract, he hypothesized that the peptide could potentially safeguard blood vessels and thereby protect tissue across every organ.
The political landscape seemed favorable for fostering international collaborations. With walls tumbling across Eastern Europe, a sense of liberation filled the air. However, war loomed as Croatia prepared to declare independence.
In the years preceding the dissolution of Yugoslavia, Sikiric re-branded the compound as BPC, an acronym with dual meanings: Bože Pomozi Croatia or “God Help Croatia,” and scientifically, “Body Protection Compound.” The label was further appended with 157, marking July 15, 1990, a date mistakenly believed to be the day Croatia would declare its independence.
When this declaration occurred the following summer, war erupted between the fledgling state and Serbian forces opposed to Croatian autonomy. Many medical faculty members were involved in the war effort, including Sven Seiwerth, a pathology professor at the university who volunteered as a medical doctor on the frontlines while having a wife and two young children to care for. “It was all about survival,” he recalled.
By 1992, other nations began to acknowledge Croatia as an independent state, and the political atmosphere finally supported the team’s efforts. Sikiric experienced a stroke of luck: Zagreb hosted a prominent pharmaceutical company, PLIVA, which was thriving due to its development of the antibiotic azithromycin.
In 1993, Sikiric entered into a contract with PLIVA, which began researching BPC-157 in collaboration with university researchers and the American company Parke-Davis.
The results were promising. For instance, a study conducted in 1995 at Parke-Davis’s facility in Ann Arbor, Michigan found that the substance helped protect rats’ colons from harsh chemicals introduced into their intestines shortly thereafter. Research conducted by a group of scientists from PLIVA and the University of Pécs in Hungary demonstrated a similar protective effect when they tested segments of the peptide in freshly isolated rat stomach cells.
PLIVA also initiated human trials for BPC-157. In the early 2000s, the company conducted two early-phase trials aimed at determining the peptide’s efficacy in treating ulcerative colitis. Though the comprehensive results were never published, a brief summary in 2005 reported that the second trial indicated a positive effect, yet it did not achieve statistical significance.
Accounts of what transpired next vary. Sikiric claims that PLIVA scientists were prepared to proceed with a Phase 3 trial and initiate additional trials to examine the peptide’s effects on wound healing. However, in 2006, the company’s research institute was sold to GlaxoSmithKline, while the remaining parts of PLIVA were acquired by Barr Pharmaceuticals, which in turn was purchased by Teva Pharmaceuticals in 2008.
The BPC-157 project was passed on to GSK but was subsequently abandoned. Sikiric contended that this was not because the drug proved ineffective or dangerous, but due to GSK’s focus on its own projects. He believes they let go of a potentially groundbreaking drug.
“When larger companies absorb smaller ones, they cherry-pick portions that fit their agenda and disregard the rest,” noted Michael Parnham, a senior scientific adviser at PLIVA during GSK’s acquisition.
Parnham, who joined PLIVA in 1998, was skeptical about the BPC-157 initiative from the outset. He found it came with a peculiar licensing agreement requiring PLIVA to advance the drug to clinical trials. (Sikiric contends the agreement was supposed to bring the drug through to marketplace availability, though he declined to provide documentation.)
Parnham also deemed the experimental results underwhelming. At PLIVA, his team published two studies comparing BPC-157’s ability to heal wounds in rats against conventional treatments. Their observations indicated that BPC-157 facilitated the early formation of granulation tissue, which comprises cells and new blood vessels essential for repair. They concluded that the peptide seemed to stimulate a particular gene involved in the body’s injury response.
However, it barely outperformed existing drugs. “In the competitive world of drug marketing and sales, convincing stakeholders that we had a superior alternative would have been exceedingly difficult,” Parnham observed.
Parnham also expressed concerns regarding how Sikiric presented the data, describing him as employing flashy slides with excessive certainty akin to a marketing pitch.
By late 2009, the licensing rights to BPC-157 were returned to Sikiric, along with all the data PLIVA had compiled. Since then, he and his team have continued their research, primarily using rodent studies. A few other research teams in Taiwan, South Korea, China, and Turkey have also published studies showing predominantly positive results with minimal reported side effects.
However, not everyone perceives a lack of side effects as advantageous. “Anything that lacks side effects likely isn’t very potent,” remarked Parnham. Furthermore, human data remains sparse. A clinical trial that began in Tijuana around 2015, sponsored by a Croatian company listing Sikiric as a part-owner, is marked as canceled in a U.S. government database. In a 2025 review, Sikiric and his team claimed that the study affirmed the peptide was “safe and well-tolerated,” but they have yet to publish the results.
A generation ago, this might have been the conclusion of the story. However, according to Luke Turnock, a criminologist in the U.K., around 2010, bodybuilders began discussing peptides in online forums, some of which seemingly led them to Sikiric’s scholarly articles. These fitness enthusiasts began sourcing peptides like BPC-157 from suppliers in China, leading to a booming gray market where BPC-157 emerged as a standout product.
While Sikiric cannot pinpoint the exact moment when he discovered that bodybuilders were using BPC-157, he recalls feeling joy comparable to that of a parent watching their child develop and thrive.
“What is the essential purpose of the drug?” he posed. “To be useful for the people.”
The utilization of BPC-157 has since extended from bodybuilders to biohackers and patients with unmet medical needs. It is now widely accessible online, often promoted as a natural substance, produced by the human body, that has been shunned by pharmaceutical companies yet embraced by medical outsiders.
The peptide has also garnered support from the MAHA movement. On an episode of his “Ultimate Human Podcast” last December, wellness entrepreneur Gary Brecka — a key player in the MAHA movement — listed several diseases and conditions he believes BPC-157 can effectively treat. He suggested to his guest, former FDA commissioner Marty Makary, that it and other unapproved peptides have yielded “astounding results.”
In March, Anna Mapp, a chemist at the University of Michigan and current president of the American Peptide Society, sat at her office table with a stack of printouts. At Undark’s request, she reviewed various BPC-157-related documents, including the Croatian team’s patent for isolating the parent protein of BPC-157.
As she spoke alongside large papier-mâché models constructed by former students, Mapp expressed surprise at the patent’s lack of detail. Not even the protein’s molecular weight was specified. “There was no evidence that I could discern demonstrating it as a single pure isolated substance,” Mapp stated. Was a single protein isolated or merely a mixture of different entities?
She highlighted the unusual fact that the complete protein sequence was never published, describing such an omission as unacceptable by contemporary scientific practices. Without the full sequence, reproducing the original findings becomes impossible — a critical aspect of quality control in scientific work.
Moreover, there is no genetic material in the human genome or gut microbiome that corresponds with the amino acid sequence of the peptide. “That is concerning,” Mapp said.
Additionally, it remains unclear how the peptide acts on the body, a concern echoed by several other researchers. “Most peptides need receptors for their activity,” wrote Patricia Brubaker, a peptide scientist at the University of Toronto, in an email to Undark. The majority of peptide drugs operate by binding to receptors on cell surfaces, initiating changes in cellular behavior. However, no dedicated BPC-157 receptor has been identified, and Sikiric has not focused his studies on discovering 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 pointed out the unusual absence of the complete protein sequence, questioning whether it is actually produced by the body.
Collectively, this evidence has raised skepticism among Mapp and other researchers regarding a significant claim in BPC-157’s origin story: They are not convinced that it is indeed a naturally occurring compound in the body.
Sandor Szabo, Sikiric’s long-time collaborator, co-authored a 2017 paper that characterizes BPC-157 as a promising candidate for preventing and treating ulcers. However, the paper simultaneously outlines the many expected details that would accompany a naturally occurring substance. If BPC-157 were genuinely produced in the body, Szabo and his colleagues argued, there would have been, over decades, a clear identification of the gene that encodes it, the cells responsible for its production, the interacting receptors, and the quantities present in the body.
Reflecting now, he speculates that the original team might have misread an amino acid sequence many years prior. At that time, the analytical techniques available for chemical analysis were still developing.
Nonetheless, Szabo remains confident that the substance can protect the stomach and small intestine. He pointed to several research teams, including his own, that have reproduced positive outcomes in cell cultures and rodent models.
It may not be a natural compound, he concluded, but “as long as it works and has no side effects, who cares?”
On a quiet evening, after most of the faculty had left for the day, Sikiric remained at his computer. A print of the Virgin Mary hung on a wall next to a stack of empty lab supply boxes. Out the window, the red rooftops of Zagreb were visible.
Sikiric scrolled through slides until he came across a passage about cytoprotection from a 1979 paper authored by Robert, the researcher who significantly influenced the field. This paper has served as a guiding light for Sikiric’s work, and he referenced it now to advocate for his project, pointing out that it does not mention receptors, suggesting to him that Robert didn’t consider them crucial for cytoprotection.
Throughout numerous discussions with Undark over the past seven months, Sikiric laid out his perspective on how BPC-157 operates within the body. He asserts that his research indicates the peptide aids in repairing damage to blood vessels and helps regulate nitric oxide levels, a molecule that relaxes blood vessels and helps prevent hypertension.
In May 2026, Sikiric and Sven Seiwerth collaborated in the University of Zagreb’s pathology building. They have worked on the BPC-157 project for over 40 years, estimating that more than 100 current and former Ph.D. students have participated in their research.Visual: Igor Nobilo for Undark
Sikiric asserts that BPC-157 stands alone in its potential benefits. He claims the peptide can encourage blood clotting when necessary and thinning at other times. It purportedly stimulates the creation of new blood vessels when healing from an injury but does not promote blood vessel growth that could fuel tumor advancement. Sikiric adamantly disputes the notion that the peptide might induce cancer.
Furthermore, he refutes the argument that BPC-157 isn’t natural. In an email response, he cited a range of papers, including findings from Taiwan, demonstrating BPC-157’s indirect impacts on two receptors associated with bodily healing. He also referenced images from his lab revealing BPC-157 in human fetal tissue cells. This evidence did not convince every researcher; one skeptic commented, “I honestly do not find these data compelling in any regard,” noting the use of immunostaining in her own studies.
If asked about the patent’s lack of detail, Sikiric would direct critics to the U.S. patent office. (This occurrence is not unique, according to Sherkow, the law and medicine professor: “Vague information is often included in patent specifications.”)
Regarding the publication of the amino acid sequence of the parent protein, Sikiric stated, if one has a child, they desire it to remain uniquely theirs.
Moreover, he argues that the benefits are evident in and of themselves.
Sikiric and Seiwerth believe their combined experience encompasses over 100 current and former Ph.D. students, many of whom are now professors and active contributors to the research team. Repeatedly, studies in tissue samples and rodent models reaffirm that BPC-157 operates effectively, usually causing minimal to no side effects.
For many Americans, this suffices. Some have reviewed the studies independently, eager to bypass FDA approval; others have heard favorable testimonials from athletes and popular podcasters. Many assert that they battle chronic issues and feel underserved by the medical community, often viewing the FDA as paternalistic and inclined towards the profit-driven pharmaceutical industry.
Such sentiments have resonated with Kennedy, who has advocated for experimental therapies in line with his broader skepticism of the medical establishment.
However, others argue that for all its imperfections, the FDA’s drug approval system ranks among the best globally. “I understand the frustration some have towards the FDA,” said Christopher Mendias, a rehabilitation clinician-scientist at Performance Medicine Institute in Phoenix, Arizona. “However, all too often, drugs showing promise in laboratory settings fail to deliver in human tests.” He added, “The FDA’s approval framework helps ensure drug safety and efficacy. Circumventing this could have dire consequences.”
More information regarding BPC-157 may be forthcoming. Christopher Robinson, a regenerative medicine and pain physician at Johns Hopkins University School of Medicine, informed Undark of his application for funding aimed at conducting clinical trials on BPC-157 and other peptides concerning chronic pain. He is seeking support from the Advanced Research Projects Agency for Health (ARPA-H), which funds high-risk, high-reward research that has the potential to disrupt health care — or fail dramatically.
For the moment, Robinson recommends that individuals “proceed cautiously” if they consider utilizing unapproved peptides. “From a scientific standpoint, I require data,” he stated. “I need valid, robust evidence before making prescribing decisions. I do not wish to offer patients unvalidated or minimally studied products.” Some experts have even more stringent views; one physician emphasized to Undark earlier this year that without rigorous data from clinical trials, BPC-157 “should not be administered to humans.”
In Croatia, Sikiric is increasingly receiving calls from reporters. He continues to collaborate with his current and former students. In interviews, many expressed a desire for clinical trials to be conducted. As one of them pointed out, the project began decades ago; for Sikiric, “It’s like a long-standing child: he needs to deliver it.”
