At a glance
| Common fragment | Ac-LKKTETQ |
|---|---|
| Fragment length | 7 amino acids |
| Parent molecule | 43-amino-acid thymosin beta-4 |
| Human efficacy | Not established for the fragment |
| US status | No FDA-approved TB-500 medicine |
Overview
The identity problem is central to understanding TB-500. An analytical study identified N-terminally acetylated residues 17–23 of thymosin beta-4, Ac-LKKTETQ, in a product sold under this name. FDA discusses the LKKTETQ fragment separately from the full 43-amino-acid peptide. Commercial use of TB-500 is inconsistent, so the name alone does not specify what is in a vial. Marketing commonly invokes tendon healing, injury recovery, angiogenesis, or muscle repair, but a plausible relationship to a natural repair-associated molecule does not establish a safe clinical treatment. This profile treats the fragment as distinct from the separate thymosin beta-4 entry.
How it works
The fragment overlaps an actin-interacting region of thymosin beta-4, which helps explain interest in cell movement and tissue repair. However, a short sequence cannot be assumed to reproduce the structure, intracellular distribution, processing, or biological actions of the full peptide. A validated human therapeutic mechanism for injected TB-500 has not been established; fragment identity and formulation must be resolved before mechanistic or outcome claims can be evaluated.
What does the name actually identify?
Mass-spectrometric characterization of a TB-500 preparation found an acetylated thymosin beta-4 fragment. This demonstrates the identity of that analyzed material, not every modern product carrying the name. Full-length thymosin beta-4, non-acetylated LKKTETQ, and acetylated LKKTETQ should be kept separate in a scientific record rather than treated as guaranteed synonyms.
Supporting sources [1]
Why parent-peptide trials are not fragment trials
A small ophthalmic study used full-length thymosin beta-4 as RGN-259 in patients with neurotrophic keratopathy. It did not test TB-500 fragment injections for tendon or muscle recovery. Different sequence, route, formulation, and disease each limit evidence transfer. The clinical result should remain attached to the product actually studied.
Supporting sources [2]
What FDA says about the fragment
FDA identifies possible immune reactions arising from aggregation or peptide impurities and states that it has not identified adequate human exposure information for the fragment. This is an evidence gap, not a demonstrated safe dose. Uncertain product identity makes adverse-effect prediction even harder when preparations are sourced outside pharmaceutical research.
Supporting sources [3]
Does being a piece of a natural peptide make it safe?
No. Fragmentation and acetylation can change biological activity, persistence, and immune recognition. Natural production of the parent molecule also differs from administering a manufactured preparation systemically. The available sources do not establish TB-500 as a treatment for tendon tears, muscle injury, chronic pain, or general recovery.
Reading this profile
Jurisdiction: United States: no FDA-approved TB-500 product; fragment and full-length thymosin beta-4 are distinct evidence subjects.. Molecular class: Ambiguous commercial name; often an acetylated seven-amino-acid thymosin beta-4 fragment.
This profile was written with AI-assisted research and checked against the linked sources. It has not been represented as a clinician’s review. Evidence summaries describe the cited studies and products; they do not establish that a separately purchased preparation is equivalent.
Sources & references
Follow the original material. Product labels define specific formulations and uses; trial registration describes a study and does not by itself establish benefit.
- Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. ↗Original research · Checked 2026-10-27
- 0.1% RGN-259 (Thymosin ß4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial. ↗Original research · Checked 2026-10-27
- FDA — bulk substances with potential significant safety risks ↗Regulatory source · Checked 2026-10-27