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Repair and regeneration peptides · Investigational

TB-500: A Fragment With No Human Trials, Sold on Another Molecule’s Research

TB-500 and thymosin beta-4 are different molecules. Every human trial in the literature used the other one.

Compiled by the PeptideCare Finder editorial team · Published 2026-08-05 · Updated 2026-07-28 · Not independently reviewed by a clinician
Regulatory and anti-doping status
FDA-approved use
None. No FDA-approved product exists for TB-500 or for full-length thymosin beta-4.
Classification here
Investigational
Compounding status
Not on the 503A Bulks List. Listed by FDA under "nominated but withdrawn" as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500". Reconsidered at the 23 July 2026 advisory committee meeting, evaluated for wound healing. FDA has published no outcome.
Anti-doping status
Prohibited at all times — WADA 2026 Prohibited List, section S2.3, listed as "Thymosin-ß4 and its derivatives e.g. TB-500". S2 substances are non-Specified Substances.

Every line above is re-verified against the primary agency source before each update. What the July 2026 FDA vote did and did not do →

What TB-500 actually is

TB-500 is a synthetic seven-amino-acid peptide corresponding to residues 17–23 of human thymosin beta-4 — the actin-binding region. FDA names it in exactly those terms. Full-length thymosin beta-4 is a 43-amino-acid protein. They are not the same molecule, and that distinction carries almost the entire weight of this page.

The substitution at the centre of the marketing

Sellers routinely justify TB-500 by pointing at "extensive thymosin beta-4 research". That research exists — Phase 1 through Phase 3 programmes in dry eye, pressure ulcers, venous stasis ulcers and cardiac repair. It used full-length thymosin beta-4. None of it tested the seven-residue fragment being sold. Citing one molecule’s trials to support another is the defining feature of how this substance is marketed.

What human evidence exists for TB-500 itself

None. Not limited, not preliminary — none. No completed human trial has ever tested TB-500. A PubMed search returns doping-detection analytical chemistry, rodent metabolite work and animal studies. FDA states the position in its own words: it "has not identified any human exposure data drug products containing Thymosin Beta-4, Fragment."

A trap worth knowing about

A search of ClinicalTrials.gov for TB-500 returns a single record that appears to be a Phase 1/2 cardiovascular trial. It is a fictional example record — its own summary opens by saying so, and it exists to demonstrate the registry’s data format. It is the first result on a routine search and is exactly the kind of thing that ends up cited as proof that human trials are underway. They are not.

What is known about safety

For TB-500 there is no controlled human safety data of any kind, because no human study has administered it. FDA’s published concern is immunogenicity risk from aggregation and peptide-related impurities, and it states it "lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans." Safety findings from full-length thymosin beta-4 trials cannot be transferred to it.

How far up the evidence hierarchy this reaches

No completed human trial has ever administered TB-500. Everything above tier 2 in the literature belongs to a different molecule — full-length thymosin beta-4.

FDA-approved label
Adverse reactions observed in trials of known size, in a defined population.
Registered human trials
Useful — but read the size. A few dozen participants cannot detect an uncommon harm.
Animal and in-vitro work This substance reaches here
Where the literature for most marketed peptides actually sits. Not evidence of human benefit.
Testimonials and forums
Not evidence. Systematically under-reports harm.
Where a substance's best available evidence sits matters more than any claim made about it.

Where it sits on the compounding pathway

01
Nominated
Someone proposes the substance for compounding use.
02
Category 2
FDA flags significant safety risks pending evaluation.
03
Nomination withdrawn
The nominator pulls it. FDA still publishes its risk language.
04 Here
Advisory committee
A non-binding recommendation. Not a decision.
05
On the 503A Bulks List
The only stage that confers authority. Reached by rulemaking.
As of August 2026 no peptide has reached stage 05. Coverage routinely reports stage 04 as though it were stage 05.

What it is sold for, against what the evidence shows

Marketing claims on the left, in the terms sellers use. What the human literature actually supports on the right.

Marketed forWhat the evidence showsVerdict
Tendon and ligament healing No human data on TB-500 at all. Tendon claims rest on rat studies. No human evidence
Soft-tissue and muscle injury recovery No human trials of TB-500. Rodent and in-vitro work only. No human evidence
Wound healing The use FDA evaluated. Human wound-healing trials used full-length thymosin beta-4, a different molecule, and none led to approval. No human evidence
Cardiac repair Full-length thymosin beta-4 only, and that intravenous trial was withdrawn with zero enrolment. No human evidence
"Backed by extensive thymosin beta-4 research" The cited literature is a different molecule. This is the central misdirection. Contradicted

Where to go next

Repair and regeneration peptides
BPC-157
Almost always sold in the same breath as TB-500. Its literature is thin, but unlike TB-500 it does at least include registered human trials.
Growth hormone secretagogues
Ipamorelin
A useful contrast: what a peptide looks like when human trials genuinely were run, and what they found.
What this guide deliberately omits

No dosing, cycling, stacking, reconstitution or administration instructions appear anywhere on this site, and this page links to no page selling an unapproved injectable. Questions about how a substance would be used belong with a licensed clinician who has evaluated you.

Sources

  1. Esposito S, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal, 2012
  2. Ruff D, et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta 4 in healthy volunteers. Ann N Y Acad Sci, 2010
  3. FDA — Certain bulk drug substances that may present significant safety risks (TB-500 entry)
  4. FDA — Pharmacy Compounding Advisory Committee, 23–24 July 2026
  5. WADA — 2026 Prohibited List, section S2.3