Scientists Challenge BPC 157 Safety Claims Citing Research Gaps and Bias

BPC 157 is a synthetic pentadecapeptide popularized largely through the prolific output of a single Croatian research group. It is widely sold as a supplement in 200 µg capsules and self-administered by longevity and performance-enhancement communities, yet its regulatory and scientific status remains contested. This reply letter, authored by Józwiak, Bauer, Kamysz, and Kleczkowska, directly responds to a comment by Sikiric et al. defending BPC 157's safety and therapeutic breadth.

The authors' central concern is one of research integrity and generalizability. A PubMed search as of May 2025 returns over 190 BPC 157 articles, with more than 80% listing Sikiric or Seiwerth as first or senior author. This extreme concentration of output within a single center creates a high risk of confirmation bias and severely limits independent replication. Furthermore, virtually all animal experiments employ only two dose levels—10 µg/kg and 10 ng/kg—leaving the dose-response relationship entirely uncharacterized.

Pharmacokenetic data complicate the picture further. An independent 2022 study in rats and dogs found plasma half-life under 30 minutes and low bioavailability after intramuscular administration. Despite this, the compound is commercially available in oral capsule form with no published human PK data supporting that route. The authors also note that a reported LD50 experiment administering 2 g/kg intravenously in mice with zero observable toxicity is biologically implausible given rapid systemic clearance and raises questions about compound purity and actual peptide content.

On the mechanistic side, the authors reject Sikiric et al.'s framing that BPC 157 merely 'balances' the NO system. They cite the group's own prior publications describing VEGF, CD34, and FVIII upregulation—hallmarks of angiogenesis stimulation—and a 2020 Taiwanese study demonstrating direct, dose-dependent eNOS activation via Src-Caveolin-1 pathway disruption in isolated aortic tissue. The authors argue that direct NO and NOx measurements, eNOS phosphorylation assays, or NOS activity studies are required to substantiate NO modulation claims, and that L-NAME or L-arginine rescue experiments alone are insufficient proof of mechanism.

Anticancer claims receive particular scrutiny. Sikiric et al. cited a 2004 melanoma cell-line abstract and a 2018 cachexia study as evidence of antitumor activity. The authors counter that neither constitutes in vivo tumor suppression data. The cachexia study addressed systemic condition in tumor-bearing animals, not tumor volume or metastasis. Asserting oncologic safety while simultaneously demonstrating pro-angiogenic signaling is, the authors argue, a logical contradiction given the well-established role of angiogenesis in tumor progression.

Clinically, the evidence base is thin. The primary registered Phase I trial (NCT02637284) was cancelled. Earlier knee-pain trials lack published results. A Phase I IBD study found BPC (as PL 14736) to be safe but provided scarce detail. A two-participant intravenous infusion report cannot be considered adequate safety evidence. The authors conclude that without independent multi-dose trials, long-term safety evaluations, rigorous PK/PD profiling, and randomized controlled trials, BPC 157 does not meet the evidentiary bar for a validated therapeutic agent.