The Zagreb Origin of BPC-157, and What Came After

The Zagreb Origin of BPC-157, and What Came After
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Science & Medicine Peptides History Research
Long-Form History

From Gastric Juice to Forum Folklore: How Two Peptides Discovered Decades Apart Ended Up in the Same Vial

A war-time Croatian lab. A 1960s NIH thymus project. A Marvel character. The strange origin story of two peptides that took thirty years to end up in the same vial — and the protocol that the internet named before pharmacology caught up.
2026 · By the Ordinary Peptides Research Team ·
Look, the part most articles get wrong about BPC-157 is where it actually came from. So let me start there. Zagreb. Autumn 1991. The country is at war — Croatia just declared independence, Vukovar is getting shelled, sirens at night. Not a great time to be running a pharmacology lab. And yet somebody is. On Šalata street, inside the medical faculty of the University of Zagreb, a guy named Predrag Sikiric is doing what pharmacologists do when funding is thin and reagents are scarce, which is, you run rats. He has been running rats for years at this point. The lab does not have much. It has him, it has his graduate students, it has what Pliva (the Croatian pharma company that will fund most of his early work) can spare, and it has, apparently, gastric juice. That's where this story starts. Not at Pfizer. Not at a Stanford spin-out. In a Croatian university lab during a war, with stomach acid. I want to keep saying that, because it never stops being weird. Most new drugs come from rainforest expeditions, or marine sponges, or some tropical soil bacterium with a name nobody can pronounce. Sikiric's group went the other direction. They asked: your stomach is the most chemically hostile environment in your body, hydrochloric acid at pH 1.5, pepsin actively dismantling proteins, all of it. Why doesn't your stomach just digest itself? There has to be a protective something in there. A peptide the body makes to keep its own digestive organ alive. So they went looking, and they found a fragment. Fifteen amino acids. Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val. That's BPC 157.
Important Notice None of this is medical advice. BPC-157 and TB-500 are research peptides. Neither has FDA approval, both are on the WADA prohibited list. This article is about how these two molecules got discovered, named, and eventually mashed together into one vial — not about whether anyone should put them into their body.

The Stomach That Healed Itself

The earliest BPC entry on PubMed is dated 1992. Eighteen authors. Sikiric and seventeen others. They describe "a new potent peptide" the team had pulled out of human gastric juice and given the name Body Protection Compound, BPC for short, because it seemed to protect a lot of different organs. Not the most elegant name in the history of pharmacology. Honest, though. Why 157? Boring answer. It refers to the position of the active fragment in the parent BPC molecule. Different fragment lengths got tested. The 15-mer kept the activity. So: BPC 157. Why those four prolines clustered near the start? That part actually matters. Proline-rich peptides resist proteolysis, which is why this thing survives gastric juice for more than 24 hours where most peptides would be torn apart in minutes. The acid stability is the whole game. Without it you have just another short chain getting digested before it can do anything. Sikiric was nobody famous when this started. A Zagreb-trained pharmacologist in a small department, in a country that had basically one notable pharmaceutical company (Pliva) and very little international visibility in drug discovery. Hungary had its biotech tradition, Czechoslovakia its chemists. Yugoslavia had Pliva and that was about it. Pliva funded chunks of the early animal work. Several 1990s papers acknowledge grants from Pliva and from the Croatian Ministry of Science. The molecule went into early human trials for ulcerative colitis under the codename PL-14736, also known earlier as PL-10 and PLD-116. If you read old patents and conference abstracts you'll see the same compound under five different labels, which is genuinely confusing but also pretty normal for that era. A cluster of papers landed in 1993. Life Sciences. Gastroenterology. Inflammopharmacology. Journal de Physiologie. The peptide protected livers, intestines, gastric mucosa. It seemed to work on basically every organ system. Which made other pharmacologists uneasy. Anything that helps everything probably helps nothing. That's the standard rule. The pentadecapeptide either broke the rule or appeared to break it. Depending on which reviewer you asked. I spent a weekend going through the Sikiric bibliography and what got me wasn't the volume, although the volume is large (more than 150 papers by some counts, more than 200 by others). What got me was how isolated the work is. Sikiric is on almost every paper. The vast majority come out of the same Zagreb department. A 2026 piece in Undark pointed out this is both a strength of the program (deep institutional knowledge) and its weakness (limited independent replication outside Croatia). For anyone who wants to dig into the molecule itself rather than its history, the scientific overview of the pentadecapeptide covers mechanism, evidence base, and regulatory status in detail. There are exceptions. A Taiwanese group in Kaohsiung published tendon-fibroblast work in Journal of Applied Physiology in 2011, looking at outgrowth and migration. Real, peer-reviewed, not from Zagreb. But it's an exception, not a pattern. The honest answer to "why has this molecule produced a hundred-plus animal papers and almost no completed human trials" is: nobody really knows for sure. Funding plays a role. Patent issues, which I'll get to. The geographic concentration of the science. Probably also some bad luck with sponsor acquisitions in the mid-2000s.

A Different Lab, A Different Decade

Now rewind. Switch continents. TB-500's parent molecule starts not in Croatia but in the mid-1960s in New York, at the Albert Einstein College of Medicine, where a young biochemist named Allan Goldstein was trying to figure out what the thymus actually did. Sounds like an odd question now. The thymus is the immune system's training ground for T cells. Textbook. In the 1960s? Emphatically not textbook. The thymus had spent the early twentieth century being dismissed as vestigial. Some pathology textbooks of the 1920s called it "a curious gland of unclear purpose." That changed in 1961 when Jacques Miller, working in Australia, showed that mice thymectomized at birth developed catastrophic immunodeficiency. The thymus was making something the immune system needed. Goldstein's group went hunting for it. In 1972 they isolated something they called thymosin fraction 5. Not a single peptide. A complex mixture pulled out of calf thymus tissue. Calf, because nobody was running clinical work on human thymus glands and the local slaughterhouse had calves. The fraction had immunological activity. Inside it, several distinct peptides eventually got names: thymosin alpha-1, thymosin beta-4, others. Goldstein eventually moved his lab to George Washington University, by the way — not the only academic move in this story, peptide research being what it is, but worth noting. In 1981, Teresa L. K. Low, working with Goldstein, published the complete amino acid sequence of thymosin beta-4. A 43-residue peptide. That's the citation everyone anchors to now when they say "Tβ4 was isolated in 1981," although honestly the truth is messier. The fraction had been around a decade earlier. What 1981 actually gave us was a sequence. So for a while everyone assumed thymosin beta-4 was an immune molecule. Came from the thymus. Thymus does immunity. Case closed. Wrong. In the early 1990s, work by Safer, Bhaskara, and others, much of it building on Hynda Kleinman's group over at the National Institute of Dental and Craniofacial Research (which is, yes, a real NIH institute, despite sounding like something somebody made up), reframed thymosin beta-4 as something completely different. A G-actin sequestering protein. Present in basically every nucleated cell in the body. Not an immune signal at all. A cytoskeletal regulator. The molecule that helps cells move around. This was a paradigm sh— no, scratch that, I'm banned from saying that phrase. Let me put it differently. The reframing was disorienting. Tβ4 turned out to be one of the most abundant intracellular proteins in mammals, hiding in plain sight, doing structural work in every cell of every tissue. The whole "immune-system molecule" story was a red herring driven by where they happened to find it first. Then 2004 happened. Bock-Marquette and colleagues published in Nature. They showed thymosin beta-4 promoted cardiac repair after myocardial infarction in mice, activating cardiac progenitor cells, reducing scar tissue. Suddenly the regenerative-medicine field cared. Nadia Smart's 2007 Nature paper extended the result. Tβ4 mobilized adult epicardial progenitors and drove neovascularization. Cardiology took notice. So did, eventually, the racetrack.

The Name "TB-500" Was Never Scientific

Thymosin beta-4 is 43 amino acids. TB-500 (the thing sold as a research chemical, the thing on peptide forums) is not actually thymosin beta-4. It is related. Based on the active region. A seven-residue fragment really, LKKTETQ, sometimes extended a few residues, identified as the actin-binding core back in the early 1990s. The label "TB-500" itself is not scientific. There is no Nature paper that uses it. No clinical trial registers under that name. By various accounts, the moniker came out of veterinary pharmacology — the equine racing world, where a synthetic Tβ4 fragment was used to support recovery from training injuries in racehorses sometime in the 2000s. The "TB" is "thymosin beta," straightforward enough. The "500" looks like a product-line identifier rather than any meaningful scientific designation. I tried to track down the actual origin, the first company that put the TB-500 label on a vial, the first product brochure, anything. I couldn't. The trail goes cold somewhere in the early-to-mid 2000s, in the kind of ambiguous space where racing supplements meet research-chemical suppliers. If you happen to know the real first use, the actual product, please send it. I'd add it. What's clear is that by the late 2000s "TB-500" was the name people used in forums and supplier catalogs, and "thymosin beta-4" was the name people used in PubMed. Same molecule? Sort of. Often. Not always. And that "not always" matters, because products sold as TB-500 are not always chemically identical to the full-length recombinant Tβ4 used in real clinical research. A 2024 study in Journal of Chromatography B by Rahaman and colleagues even raised the possibility that the active form in vivo might be a metabolite (Ac-LKKTE), not TB-500 itself.

Two Solutions, Looking for a Problem

By the mid-2000s both peptides existed in their own respective worlds. BPC-157 was a Croatian academic program with a small clinical trial in inflammatory bowel disease and a slowly accumulating animal-data file. Pliva, its sponsor, got acquired by Barr Laboratories in 2006 and then by Teva in 2008. The clinical pipeline drifted. A phase-II ulcerative-colitis trial under the PL 14736 designation produced data, but the regulatory path for a Croatian-discovered peptide through US or European drug approval was, well, complicated. No major sponsor picked it up afterwards. TB-500 was floating around the equine world and quietly seeding itself into bodybuilding forums. WADA put it on the prohibited list by 2011. S2 class, peptide hormones. WADA does not bother banning compounds that nobody is using. The ban is itself a historical marker. The cat was out of the bag. Both molecules shared a structural problem. They weren't patentable as new chemical entities (the underlying sequences were either natural or had prior art). They weren't moving through formal trials. And they had a small but very motivated user base of athletes, weekend tinkerers, and a handful of regenerative-medicine clinicians. The mainstream pharma industry didn't want them. Veterinary medicine and the gym crowd did. If you stack up the obstacles that kept BPC-157 and TB-500 out of mainstream pharmacology, the list looks roughly like this:
  • No new-chemical-entity patent. Natural sequences (BPC) and natural fragments (TB-500) cannot be patented as novel composition of matter, which is the kind of patent that funds Phase III trials.
  • No deep-pocketed sponsor. Pliva moved through two acquisitions (Barr 2006, Teva 2008), and BPC-157's clinical pipeline drifted in the process. TB-500 never had a comparable pharma sponsor at all.
  • Geographic concentration of the data. The vast majority of BPC-157 papers come from the same Zagreb department, which makes the evidence base look fragile to outside reviewers regardless of whether the work is sound.
  • An impatient parallel market. Veterinary medicine, the equine-racing world, and bodybuilding forums adopted both compounds long before formal pharmacology had finished its job — and the parallel market kept growing whether or not the trials caught up.
What happened next was, looking back, pretty predictable.

Where Forums Met Pharmacology

If you have ever read a peptide forum thread, you know roughly the shape. Somebody posts a logbook of injuries and a self-experiment. Other people chime in with anecdotes. Eventually a name crystallizes for whatever protocol seems to be working. The science, where it gets cited at all, gets cited by abstract title with the URL pasted in at the bottom. The "Wolverine Stack" name came out of this kind of conversation. Or this kind of mess, depending how generous you want to be about it. So by various accounts — and the accounts vary, that is the whole problem — somewhere on MESO-Rx or MuscleChemistry or one of those lifting-and-pharmacology boards from the late 2000s and early 2010s, somebody posts their experience pairing BPC-157 (still pretty obscure outside Croatia at that point) with TB-500 (already on the athletic radar). And the poster's argument is roughly: the combination is greater than the sum. BPC works locally near the injury site, TB-500 works systemically through cell migration, you pair them up and you get coverage on both axes. That was the pitch. People tried it. Other people copied. The thing snowballed. The name? Marvel. The X-Men character with the mutant healing factor. Logan. The guy who regenerates from a gunshot in three panels. Because nothing says "rigorous science" like naming your peptide protocol after a comic-book mutant. I mean that affectionately and not dismissively, by the way. The name is at least honest about what it is. Never tried to be a clinical designation, never pretended to be more than a colloquial label. Which, compared to a lot of supplement marketing, is refreshing. The exact origin of the term is genuinely lost. I went through old MESO-Rx threads, archived Reddit posts on r/Peptides, a couple of Wayback Machine captures of bodybuilding boards from 2010 to 2013, and I could not find a single "first post." What I found was a slow drift. Scattered mentions in 2010-2011. More frequent ones by 2012-2013. By around 2014-2015 the term had stabilized. Three labs (Zagreb, Seoul, Kaohsiung) had been publishing on the pentadecapeptide individually. None of them, as far as I can tell, ever used the word "Wolverine" in print. Which is one of the things I find genuinely weird about the history of these molecules. The naming convention, the part that determined how they would be discussed for the next decade, happened entirely outside the scientific literature. The peer-reviewed papers said "pentadecapeptide BPC 157." Forums said "BPC." Often without the "157." That casual elision, the dropped digits, is itself a forum-cultural marker. If somebody writes "BPC and TB" in a thread they are a regular. If they write "the pentadecapeptide BPC 157 and the synthetic actin-sequestering analogue of thymosin beta-4" they are either a scientist or a lawyer. The forums also did something the literature didn't do. They wrote about combining the two. Almost every academic paper on the pentadecapeptide studied it alone. Almost every academic paper on Tβ4 studied it alone. The pairing, the whole idea of the pairing, came out of people who were not running controlled experiments, were not blinded, had no IRB approval, but had between them thousands of self-reports about tendons and shoulders and torn rotator cuffs and stubborn Achilles problems. Plus a strong incentive to compare notes.
By the time more formal scientific interest in the combination caught up, the lay community had been running its uncontrolled, unblinded, n-of-many experiment for more than a decade.

The Lab That Caught Up Late

Here is what I went looking for. A clean, well-controlled animal study comparing BPC-157 alone, TB-500 alone, and the two together, in the same model, with the same endpoints. Four arms, including placebo. The kind of study that would actually let you say "the combination outperforms either compound alone." It does not really exist. What exists, on the human side, is a single retrospective chart review by Lee and Padgett (2021), published in Alternative Therapies in Health and Medicine. Sixteen patients with chronic knee pain received intra-articular injections of BPC-157, some of them combined with thymosin beta-4. Fourteen of sixteen reported meaningful pain relief at six to twelve months. That sounds great until you look at the design: no control group, no placebo, no blinding, no standardized outcomes, and the BPC-only and BPC+Tβ4 groups pooled together in the analysis. Which means the study cannot tell you whether adding TB-500 to BPC-157 did anything at all. It is the only published human work involving the combination, and it is not designed to answer the question people most want answered. Beyond Lee and Padgett, the human exposure is thin. A 2024 pilot in interstitial cystitis (twelve patients, BPC-157 alone). A two-person IV safety study in 2025. That is roughly it. The systematic review by Vasireddi and colleagues in American Journal of Sports Medicine (2025) screened 544 papers and found exactly one clinical study that met inclusion criteria. The rest were animals.
Lee & Padgett, 2021 — retrospective knee study 16 patients, intra-articular BPC-157, some combined with Tβ4. 14/16 reported pain relief at 6–12 months. No control group; combination and BPC-only arms pooled. Cannot demonstrate combination superiority over BPC-157 alone.
Lee et al., 2024 — interstitial cystitis pilot 12 patients with severe IC unresponsive to standard therapy received intravesical BPC-157. All 12 reported 80–100% symptom resolution at 6 weeks. No adverse events. Single-arm, no controls.
Lee & Burgess, 2025 — IV safety pilot 2 healthy volunteers, 10 mg and 20 mg IV BPC-157. No clinically meaningful changes; plasma cleared within 24 hours. n=2 is a hint, not a safety profile.
Three studies. Roughly thirty people. All from the same clinical practice. None placebo-controlled. That is the entirety of the published human evidence base for either compound, and as you can see, none of it is designed to test the combination claim that the forums have been making for ten years. What we have instead is mechanistic plausibility. The pentadecapeptide's animal work points toward angiogenesis, growth-factor signaling (VEGF, FGF), tendon-bone interface healing. TB-500's animal work points toward systemic cell migration via actin polymerization, plus its own contribution to angiogenesis. The mechanisms partially overlap, partially complement each other, and the theoretical case for combining them is pretty reasonable. The empirical case, in the strict pharmacological sense, is extrapolated. What happened next isn't entirely clear.

An Unstudied Standard

So why did formal pharmacology never catch up? The honest answer is structural. Both peptides are, more or less, off-patent for new chemical entity claims. The underlying sequences are either natural (BPC) or based on natural fragments (TB-500). Pharma companies make money on patentable molecules. Nobody is going to spend $50 million on a phase-III combination trial for a stack they cannot exclusively sell at the end. This is a recurring pattern across the broader category of regenerative peptides. Not unique to the Wolverine Stack at all. It is why a lot of interesting peptides, including some with much stronger early-stage data than these two, never make it down a clinical-trial-led approval pathway. The math doesn't add up for a sponsor. What you get instead is orphan-compound culture. Molecules living in research-chemical catalogs, in compounding-pharmacy formularies, in veterinary use, in the gray zone between prescription medicine and supplement. They acquire reputations rather than approvals. The reputations are sometimes accurate, sometimes wildly inflated, and there is no FDA review to sort the two. The regulatory weather has actually been moving lately. The FDA's 503A compounding category placed both compounds on its Category 2 list in 2023 (substances with significant safety concerns, effectively blocking compounding pharmacies from working with them). Then in early 2026, after the original nominators withdrew their nominations and following public statements by HHS Secretary Robert F. Kennedy Jr., the FDA signaled that around fourteen of the nineteen Category 2 peptides would move back toward Category 1 — which permits prescription compounding, though not full approval. None of this is a finding that the molecules are safe. It's procedural movement. But it changed the regulatory weather around these compounds in the United States meaningfully.

A Story Still Being Written

OK, back to Zagreb. 1991. Sikiric and the rats. He had no way of knowing, sitting there in a department under wartime austerity, that the molecule he was characterizing would, thirty-something years later, end up sharing a vial with another peptide worked out at the NIH starting in the late 1960s. Could not have predicted it would get named after an X-Men character. Probably had not even read X-Men comics, though I am guessing at that part. The thing I keep wanting to say about this whole arc, and the reason I bothered writing it up, is that it's a pretty bad fit for how science imagines drug discovery should go. The clean version goes: lab, animal model, phase I, phase II, phase III, FDA, prescription pad. The actual version for these two molecules went: lab, animal model, twenty more animal models, a small phase II that didn't quite go anywhere, a forum thread, a veterinary product, a comic-book nickname, a TikTok page, a compounding-pharmacy bottle. Different shape entirely. So that's the path. Or one of the paths. Not the one anyone teaches in pharmacology school. Does the combination actually work? Is the synergy real or just plausible? Is the long-term safety profile fine? Would a real human trial back up the anecdotes? I don't know. The molecules are still under-researched where it counts. The forums know more about how to use them. The journals know more about how they work mechanistically. Nobody has the full thing. The early Sikiric papers had a line that has stuck with me. The peptide is "native and stable in human gastric juice for more than 24 hours." That claim is from 1993, before any of the rest of this happened — before the forums, before TB-500 got renamed from Tβ4, before the Marvel branding, before any of it. And thirty years on that is still, weirdly, the most well-established thing anybody can say about BPC-157. The rest is still being written.
Editorial Disclosure Ordinary Peptides supplies research-grade BPC-157 and TB-500 as separate vials and as a combined research preparation. This article is editorial. Product specifications, certificate-of-analysis references, and reconstitution math live on the product page itself, not here.

Sources & Further Reading

  1. Sikiric P. et al. Life Sciences, 1993; 53(16): PL261-6. pubmed.ncbi.nlm.nih.gov/8412502
  2. Sikiric P. et al. The Stable Gastric Pentadecapeptide BPC 157 Pleiotropic Beneficial Activity. Pharmaceuticals, 2024. pubmed.ncbi.nlm.nih.gov/38675421
  3. Low T.L.K., Hu S.K., Goldstein A.L. Complete amino acid sequence of bovine thymosin beta 4. Proceedings of the National Academy of Sciences, 1981.
  4. Bock-Marquette I. et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature, 2004.
  5. Smart N. et al. Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization. Nature, 2007; 445(7124): 177-182.
  6. Goldstein A.L. et al. Thymosin beta4: a multi-functional regenerative peptide. Expert Opinion on Biological Therapy, 2012; 12(1): 37-51. pubmed.ncbi.nlm.nih.gov/22074294
  7. Chang C.H. et al. The promoting effect of pentadecapeptide BPC 157 on tendon healing. Journal of Applied Physiology, 2011. journals.physiology.org/doi/full/10.1152/japplphysiol.00945.2010
  8. Lee E. & Padgett B. Intra-articular injection of BPC 157 for multiple types of knee pain. Alternative Therapies in Health and Medicine, 2021.
  9. Lee E. et al. Intravesicular BPC-157 for interstitial cystitis. Alternative Therapies in Health and Medicine, 2024.
  10. Lee E. & Burgess S. Safety of Intravenous Infusion of BPC157 in Humans: A Pilot Study. Alternative Therapies in Health and Medicine, 2025. pubmed.ncbi.nlm.nih.gov/40131143
  11. Vasireddi N. et al. Emerging Use of BPC-157 in Orthopaedic Sports Medicine: A Systematic Review. American Journal of Sports Medicine, 2025. pmc.ncbi.nlm.nih.gov/articles/PMC12313605
  12. Rahaman K.A. et al. Simultaneous quantification of TB-500 and its metabolites. Journal of Chromatography B, 2024; 1235: 124033.
  13. FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Category 2 designation, 2023. fda.gov/drugs/human-drug-compounding/…
  14. WADA Prohibited List. wada-ama.org/en/prohibited-list
  15. USADA. BPC-157: Experimental Peptide Creates Risk for Athletes. usada.org/spirit-of-sport/bpc-157-peptide-prohibited
  16. Undark & STAT News, 3 February 2026. "BPC-157: A MAHA-Adjacent Peptide, Linked to Croatia." undark.org/2026/02/03/bpc-157-peptide-fda
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