Superpower peptides available for pre-order. Get first access.

Not FDA-approved

Bones & muscles

TB-500

Also called thymosin beta-4 fragment

EvidenceLimited research
ClassSynthetic Tβ4 fragment

TB-500 is a synthetic thymosin beta-4 fragment sold as a research peptide. Learn what the evidence shows, why it is banned in sport, and its regulatory status.

Reviewed by
William Maish, MD MBA MPH, Clinical Product Lead
Published
April 18, 2026
Last updated
October 29, 2026

Key takeaway

TB-500 is a synthetic fragment marketed as a "thymosin beta-4 fragment" for injury recovery, and it is banned in sport. No human trial of the fragment exists. The best controlled human data belong to the full-length protein: a Phase III eye-drop trial in neurotrophic keratopathy. TB-500 is not FDA-approved, but since October 2026 the FDA allows 503A pharmacies to compound it under enforcement discretion while formal rulemaking remains pending.

At a glance

FDA statusNot FDA-approved, sold in the wellness/gray market
What it isMarketed as a synthetic fragment of thymosin beta-4, for recovery and soft-tissue injury
ResearchNo human trials of the fragment; claims are extrapolated from the full-length protein
Sport and FDAProhibited in sport by WADA at all times; compoundable by 503A pharmacies under FDA enforcement discretion since October 28, 2026, though it remains unapproved
Evidence strengthLimited research

What is TB-500?

TB-500 is a synthetic peptide sold for recovery and injury repair, commonly described as the actin-binding fragment of the natural protein thymosin beta-4 (a short piece of that larger molecule, not the full 43-amino acid protein). An important caveat is that gray-market labeling is inconsistent: material sold as "TB-500" sometimes contains the full-length protein or other fragments. It is not an approved medicine.

How does it work?

TB-500 is assumed to share the actions of full-length thymosin beta-4, namely:

  • Binding the cell-structure protein actin
  • Promoting cell migration
  • Promoting blood-vessel formation
  • Promoting reduced inflammation

A review of the full-length protein's regenerative biology1 adds the mobilization of stem and progenitor cells and less scarring, across skin, eye, heart, and brain repair models. Importantly, this is largely extrapolated from the full-length protein's animal data; the fragment itself has far less dedicated study. This describes a proposed mechanism, separate from demonstrated benefit in people.

Is it FDA-approved?

No. TB-500 is not approved by the FDA. As neutral regulatory facts: On July 23, 2026, the FDA's Pharmacy Compounding Advisory Committee voted 8-6, with one abstention, to recommend TB-5002 (free base and acetate) for the 503A compounding list, citing wound healing. On October 28, 2026, the FDA granted enforcement discretion6 allowing 503A pharmacies to compound TB-500 (along with five other peptides) while the formal rulemaking to add it to the 503A bulks list is still pending. This permits licensed pharmacies to compound TB-500, but it is not the same as FDA approval, it carries no stated end date, and it does not reflect any new finding that the fragment is safe or effective. The same coverage of the meeting lists TB-500 among the peptides voted on and does not list full-length thymosin beta-4. In sport, it is treated as thymosin beta-4 and is prohibited at all times under the WADA list.

What does the research show?

There is essentially no human evidence for the fragment. There are no completed human efficacy trials of the TB-500 fragment, and human safety data specific to it are not published. The only clinical data belong to the full-length protein, thymosin beta-4, which has been tested only in small, early trials, such as a randomized dose-escalation venous-ulcer study3 designed to assess safety and tolerability, and a Phase III eye-drop trial in neurotrophic keratopathy4. Those results do not directly transfer to the fragment. So the marketed recovery benefit is unproven in people.

More for bones & muscles

Sources: the human evidence for the related full-length protein is limited to small early trials (for example Guarnera et al., Annals of the New York Academy of Sciences, 2007, DOI: 10.1196/annals.1415.0035), indexed on PubMed; reporting on the July 2026 FDA advisory committee vote2; and the WADA Prohibited List. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.