Reviewed & approved by Dr. Nova Reyes · Last checked 2026-10-26. ← Back to Evidence Library

B7-33: what the evidence says

Name: B7-33
Creator: Dr. Nova Reyes
Published: 2026-10-26

At a glance

What it is: a lab-made single-chain peptide based on the B-chain (residues 7-33) of human relaxin-2, made at the Florey Institute in Melbourne. Relaxin is a hormone that relaxes blood vessels and fights scarring (fibrosis). B7-33 switches on its receptor, RXFP1, in a "biased" way. ^{R1, R2}

What the evidence says: in mice and rats it reduced heart, kidney and lung scarring and protected heart tissue after a heart attack, similar to full relaxin. ^{R1, R3, R4, R5} No human study exists.

Biggest risks: unknown in people. Full relaxin (serelaxin) failed its large heart-failure trials. UNVERIFIED serelaxin trial outcome not re-checked in this batch.

Rating


Human Human evidence	None
Animal Animal / lab evidence	Mouse and rat fibrosis, heart-attack and blood-vessel studies; implant coatings ^{R1, R3, R4, R5, R6}
Regulatory	Never approved · Not on FDA 503A or 503B bulk lists · WADA 2026: not named; likely S0 Caution ^{R7, R8, R9}
Established human dose	None. Study details lists what studies used

Evidence verdict: Heart, kidney or tissue fibrosis in people: No human data · Anti-fibrosis and heart protection: Animal/lab only Card verdict: No human data (heart, kidney & lung anti-fibrosis claims rest on rodent and cell studies only) Card note: Animal/lab only, see page

This page reports what studies used. It is not dosing advice.

Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source

About the evidence: almost all papers come from the inventors' network (Florey Institute and Monash University, Melbourne) plus a US heart group. ^{R1, R4, R3} The inventors' own later work found B7-33 binds the receptor weakly in some cell types, which they are trying to improve. ^R10

What is it?

Full relaxin has two chains and three disulfide bonds and is costly to make. B7-33 is a simpler one-chain mimic. Related pages: TB-500, BPC-157, SS-31.

Does it work?

Animal Fibrosis (Hossain 2016): reduced scarring in mouse models of lung and heart fibrosis. UNVERIFIED model list from abstract summary. ^R1
Animal Heart attack (Devarakonda 2020): less harmful heart remodeling in mice. ^R3
Animal Heart muscle injury (Alam 2023): kept relaxin's heart protection and reduced scarring faster than the blood-pressure drug perindopril in mice. ^R4
Animal Blood vessels (Marshall 2017): matched relaxin's vessel-protective effects in rats. ^R5
Animal Implants: coatings releasing B7-33 reduced scar capsules around implants. ^R6
Unknown No human study.

Is it safe?

Unknown No human safety data.
Unknown Relaxin lowers blood pressure and affects reproductive tissue; whether B7-33 does the same in people is unknown.

Gray-market "research use only" B7-33: extra risks

A gray-market vial has no quality control and no guarantee of identity, strength or sterility. We test retail vials blind under the Open Peptide Standard; see /tests/. A passing test covers one batch on one date and does not mean the compound is safe.

What we don't know

Unknown Any human effect or safety
Unknown How long it lasts in the body (it is unstable in serum; lipidated versions are being designed) ^R11

Is it legal?

US (FDA): never approved. Not on the 503A or 503B bulk lists, so there is no compounding route. ^{R7, R8}
Athletes: not named on the WADA 2026 list. UNVERIFIED likely covered by S0. ^R9

Study details

These are amounts researchers used, not recommendations. | Study | People / model | Route | Amount used | Follow-up | Reported | Citation | |---|---|---|---|---|---|---| | Marshall 2017 | Rats | IV, once | 13.3 µg/kg (serelaxin 26.6 µg/kg) | 3 hours and longer | Matched relaxin vessel effects | [PMID 28478069](https://pubmed.ncbi.nlm.nih.gov/28478069/) | | Alam 2023 | Mice, heart injury | Subcutaneous | Caution not in abstract | Days–weeks | Less scarring | [PMID 36753958](https://pubmed.ncbi.nlm.nih.gov/36753958/) |

Full reference list (PubMed, CT.gov, FDA and WADA checked Oct 26, 2026)

^R1 Hossain MA, et al. Chem Sci. 2016. PMID 30155023
^R2 Praveen P, et al. Mol Cell Endocrinol. 2019. PMID 30641102
^R3 Devarakonda T, et al. J Am Heart Assoc. 2020. PMID 32295457
^R4 Alam F, et al. Biomed Pharmacother. 2023. PMID 36753958
^R5 Marshall SA, et al. Eur J Pharmacol. 2017. PMID 28478069
^R6 Welch NG, et al. ACS Appl Mater Interfaces. 2019. PMID 31713411
^R7 FDA, 503A bulk drug substances categories list (updated May 14, 2026). https://www.fda.gov/media/94155/download
^R8 FDA, 503B bulk drug substances categories list (updated Mar 21, 2025). https://www.fda.gov/media/94164/download
^R9 WADA. The 2026 Prohibited List, S0. https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf
^R10 Handley TNG, et al. Int J Mol Sci. 2023. PMID 37628851
^R11 Praveen P, et al. Int J Mol Sci. 2023. PMID 37047588

Disclaimer

This page is for education and harm reduction, not medical advice or a recommendation to use B7-33. Talk to a clinician you trust, especially if you have heart disease, low blood pressure, are pregnant, or are a tested athlete. Report problems to FDA MedWatch (https://www.fda.gov/safety/medwatch).