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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

B7-33

Relaxin Single-Chain Peptide

Evidence grade 1 of 5, Untested. Read how the Atlas grades evidence.

B7-33 is a single-chain, functionally selective (biased) agonist of the relaxin receptor RXFP1, first reported by Hossain, Bathgate, Samuel and colleagues in Chemical Science (2016), which preferentially drives ERK1/2 phosphorylation and MMP-2 mediated anti-fibrotic signaling over cAMP. All supporting data are preclinical: rodent models of myocardial-infarction and isoproterenol heart failure, ovalbumin allergic airways disease, ex vivo preeclampsia-model mesenteric arteries, and B7-33-coated implants in mice. There are zero human clinical trials of B7-33, no FDA approval, and it is sold only as a research chemical, so the honest grade is animal/in-vitro-only (1).

FDA
No FDA approval; preclinical research compound only, sold as research chemical not for human use
WADA
Not prohibited

Reference only. Not medical advice.

What can go wrong

Research chemical only; no human clinical data, no established human dose, purity and safety unverified.

Talk to a clinician before taking this. The Atlas can tell you what has been studied about B7-33. It cannot tell you how it would interact with your body, your history, or anything else you are taking, and nothing on this page is a reason to start.

A single-chain functional analog of the hormone relaxin, designed for anti-fibrotic effects without relaxin's synthesis complexity. Research interest for organ fibrosis (heart, lung, kidney).

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Anti-fibrotic research (heart, lung, kidney)
  • Tissue remodeling

How it is supposed to work

B7-33 is a single-chain peptide derived from the hormone relaxin, designed to activate the relaxin receptor and deliver relaxin’s anti-fibrotic, tissue-remodeling effects in a simpler, more drug-like form. Its main research focus is reducing fibrosis (scarring) in the heart, lungs and kidneys.

B7-33 is a synthetic single-chain peptide built from a portion of the B-chain of human relaxin-2, with a short solubility tail added. It acts on the relaxin receptor RXFP1 and, unusually, is a biased agonist, preferentially switching on one of that receptor’s two signaling routes.

Type
Relaxin-derived peptide
Source
Relaxin-2 B-chain
Receptor
RXFP1, biased
Action
Anti-fibrotic
Half-life
About 6 minutes
Status
Preclinical

Relaxin’s Anti-Fibrotic Half, Designed Around The Cancer Risk, Untested In People

B7-33 is one of the more intelligently designed peptides in this library, and the design choices are the heart of its story. Native relaxin is a potent anti-fibrotic, vasodilatory and cardioprotective hormone, but it is a complicated two-chain, triple-bonded molecule that is unstable and hard to synthesize, and its recombinant version, serelaxin, failed its major heart-failure trial. B7-33 simplifies relaxin to a single chain that is easier to make, and it does something clever at the receptor: it preferentially activates the protective pERK pathway, which drives production of a collagen-degrading enzyme that breaks down scar tissue, while largely avoiding the cAMP pathway that has been linked to relaxin’s tumor-promoting effects. In line with that design, it did not promote prostate cancer in testing. The result is strong preclinical anti-fibrotic data: it prevented or reversed scarring in the heart, lungs and kidneys of rodents with potency similar to relaxin, and in one model reduced heart fibrosis faster than a standard ACE inhibitor. The honest limits are substantial. All of this is preclinical, with no human trials, no approval and no established dosing; the peptide has a very short half-life, around six minutes, requiring chemical modification to be practical; and the broader relaxin approach carries the cautionary precedent of serelaxin’s trial failure.

Safety in detail

All B7-33 evidence is preclinical (rodent and in-vitro). It has no FDA approval, no completed human trial, and is marketed for laboratory research use only. The related full-length relaxin drug serelaxin was rejected by the FDA after its confirmatory trial failed, so even the parent molecule lacks approved-drug status.

  • B7-33 is a preclinical research peptide with no established human safety data.
  • Its anti-fibrotic effects are shown in animals, not proven in people.
  • Any consumer material would be gray-market and unverified.
  • Not approved for any use.

Children and teenagers

B7-33 has no validated pediatric use and is an unapproved injected research peptide. There is no appropriate pediatric use.

What people get wrong

Nothing recorded here yet. There is almost certainly something people get wrong about this one, and the blank space means we have not written it down, not that the record is clean.

Who profits, and who pushes back

Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.

B7-33 reaches users through the gray-market research-peptide trade, sold for anti-fibrotic, cardiovascular and recovery purposes on the strength of its rodent data. There is no approved product, and the relaxin and RXFP1 field as a whole has yet to deliver a successful drug.

How we got here

B7-33 originates from the Australian relaxin research program, principally the laboratories of Ross A. D. Bathgate, Mohammed Akhter Hossain and Chrishan S. Samuel across the Florey Institute, the University of Melbourne and Monash University. It was engineered as a single-chain, low-cost simplification of the two-chain hormone H2 relaxin, whose recombinant drug form serelaxin (RLX030, Novartis) was in Phase III human trials for acute heart failure at the time B7-33 was first published in Chemical Science in 2016. Serelaxin ultimately failed its confirmatory RELAX-AHF-2 trial and was never approved, which is part of why interest shifted toward simpler analogs like B7-33 and later lipidated and further-minimized single-B-chain derivatives. B7-33 itself never entered human clinical development and today circulates almost entirely as a research chemical sold by peptide vendors.

B7-33 was developed in 2016 by an Australian group seeking to simplify the fragile relaxin hormone into a stable, easily made single-chain agonist that preserved its anti-fibrotic benefit while engineering out a tumor-linked signaling route. It reversed organ fibrosis across numerous rodent studies, while its short half-life drove ongoing work on stabilized and oral forms.

The numbers behind the grade

Type
Relaxin-derived peptide
Action
Anti-fibrotic
Targets
Heart, lung, kidney
Stage
Preclinical
Approved
No
Use
Research

The people taking it

A relaxin-derived anti-fibrotic research peptide of interest for scarring diseases, but preclinical and not a consumer compound.

B7-33’s users are recovery- and longevity-focused biohackers interested in fibrosis, scarring and cardiovascular health, plus the researchers pursuing relaxin-based anti-fibrotic therapy.

Studied in research as an anti-fibrotic relaxin analog for organ scarring; it has no approved consumer use.

Set against the alternatives

B7-33 sits among the anti-fibrotic and cardiovascular-protective peptides, near Angiotensin 1-7, the tissue-protective ARA-290, and the cardiac peptide Apelin-13, all of which share strong preclinical promise and no human proof. What distinguishes B7-33 is its deliberate design to keep relaxin’s benefit while engineering out a tumor-linked signaling route, a level of rational tailoring beyond most gray-market peptides, though it remains just as unproven in people.

What we do not know

  • Whether its anti-fibrotic effects translate to humans.
  • Which fibrotic diseases it might best address.
  • What its safety profile is, currently uncharacterized.

The market for this

What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.

There is no approved consumer route. It exists mainly as a research compound; given the limited human data, self-experimentation is not advisable.

Not produced as an approved drug for this use; any consumer-facing material is research-use-only, typically synthesized overseas in China, with no quality assurance and frequently no certificate of analysis.

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about B7-33.

  • Timeline. We have not built the dated record of research and regulatory events.
  • Supply chain. We have not mapped where it is made.
  • What could change. No forward-looking summary yet.

Sources

The studies that matter

  • Anti-fibrotic studies2010s-2020s

    B7-33 reduced fibrosis in models of heart, lung and kidney disease, the basis for interest in it as a fibrosis therapy.

  • Relaxin-receptor design2010s

    It was engineered to retain relaxin’s beneficial receptor signaling in a single-chain, more practical molecule.

  • Human trialsnone established

    B7-33 remains preclinical, without established human trials.