SECTION 00 · LKKTETQ · A WALL-LABEL READING
Is TB-500 a prescription drug? The wall label, not the marketing copy.
TB-500 is a synthetic seven-amino-acid fragment of Thymosin Beta-4. The forty-three-amino-acid parent peptide has reached Phase III in ophthalmology and a halted Phase II in cardiology. The fragment has never been in a registered human trial; individual prescription access adds no clinical-trial evidence or FDA approval.
The wall label, briefly
TB-500 is a seven-amino-acid synthetic peptide — the sequence Ac-LKKTETQ, residues 17 to 23 of the parent protein Thymosin Beta-4. Most of the encouraging science in this field used the full 43-residue protein, not this fragment. No controlled human trial has ever run on the fragment itself. FDA records TB-500 among substances whose nominations were withdrawn, separate from the active Category 2 table; its safety concerns remain beside the entry, and withdrawal grants no compounding permission [26]. WADA classifies it as prohibited for competitive athletes. Patient-specific TB-500 prescribing is separate from FDA approval of the compounded product. Read what the research record actually says and what people using TB-500 report anecdotally.
What this site is, and what it isn't
TB-500 Prescribed is a reading room. It is not a clinic, not a pharmacy, not a vendor, not a telehealth service. It does not sell TB-500 and it does not write prescriptions. Neither TB-500 nor full-length Thymosin Beta-4 has an FDA-approved product.
A patient-specific prescription does not establish FDA approval. That is the wall label.
The sections that follow walk through the chemistry, the animal work, the human trials of the parent peptide, the FDA's compounding record, and the World Anti-Doping Agency's continuing position [1][26]. Where the published evidence is strong, it is described in detail. Where it is thin, that thinness is named. Where vendor literature has filled the gap with confident dosing tables, those tables are noted as vendor literature and not treated as clinical recommendations [22].
Fragment, not full peptide
The molecule sold and discussed under the name TB-500 is N-acetyl-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, a synthetic peptide of seven amino acids carrying CAS 885340-08-9 and a molecular weight of roughly 889 Da. It corresponds to residues 17 through 23 of native human Thymosin Beta-4 (Tβ4), a 43-amino-acid intracellular peptide encoded by the TMSB4X gene and expressed in essentially every nucleated cell type [1][25].
Those seven residues contain the central LKKTET motif, the actin-binding region that does most of Tβ4's signature work — binding monomeric G-actin in a one-to-one complex and blocking its addition to growing filaments [1][2]. The fragment retains the binding sequence; it does not retain most of the parent peptide's downstream interaction surfaces.
This distinction matters because nearly every published animal study of Thymosin Beta-4 — the corneal-healing work, the cardiac-repair work, the stroke work, the hair-follicle work — was performed with the full 43-residue molecule [3][4][6][7][12][24]. Every registered human clinical trial likewise used full-length recombinant Tβ4, not the fragment [13][14][15][16][17]. The FDA cited that identity gap — fragment marketed, parent peptide studied — in its safety discussion of TB-500 [26].
What the research actually shows
Read as a body of work, the Thymosin Beta-4 literature is consistent on a few things and unfinished on most.
It is consistent on mechanism. Tβ4 binds monomeric actin one-to-one through its LKKTET core [1][2]. It induces angiogenesis, including VEGF expression in endothelial cells [25]. It activates the PINCH-Tβ4-ILK signaling complex upstream of Akt, which promotes cardiomyocyte survival and migration after ischemic injury [6][7]. It directly inhibits NF-κB transactivation, which dampens inflammation independent of its actin work [11].
It is consistent on small-animal wound healing. Topical Tβ4 accelerated re-epithelialization of full-thickness rat skin wounds by 42% at four days and 61% at seven days [3]. Topical Tβ4 accelerated corneal healing after alkali burn in mice [4]. Both observations have been replicated, including in diabetic and aged mouse models [5].
It is unfinished on humans. Phase I IV safety trials of full-length recombinant Tβ4 — one in the United States in 40 volunteers up to 1,260 mg [13], one in China in 84 volunteers up to 25 μg/kg [14] — established acceptable tolerability and no serious adverse events. The Phase III ARISE-3 trial of topical RGN-259 (a 0.1% Tβ4 ophthalmic solution) in roughly 700 dry-eye patients missed its prespecified co-primary endpoints, though it produced significant improvement in ocular grittiness and in a defined-subpopulation corneal-staining measure [15]. An earlier Phase III neurotrophic-keratopathy trial of the same product showed 60% complete corneal healing at day 29 in treated subjects versus 12.5% in placebo (p=0.066) and statistically significant healing at day 43 (p=0.036) [16]. The cardiac program, RGN-352, enrolled into Phase II with 450 mg or 1,200 mg IV regimens after acute myocardial infarction, was placed on FDA clinical hold in 2011 over contract-manufacturer cGMP issues, and has not reported efficacy [17].
A prescription and an approval answer different questions
Prescribing includes FDA-approved drugs and patient-specific compounded preparations. Off-label prescribing concerns an unapproved use of an approved drug. A compounded preparation has no FDA approval of its own.
No TB-500 product is FDA-approved. No full-length Tβ4 product is FDA-approved either. RGN-259 and RGN-352 remain investigational [15][16][17]. No marketing authorization has been granted by the EMA, MHRA, TGA, PMDA or any comparable agency. An individual prescription for a compounded preparation is distinct from either an approved indication or off-label use of an approved drug.
FDA's Bulk drug substances nominated but withdrawn table includes Thymosin Beta-4, Fragment (LKKTETQ), the TB-500 fragment, alongside the agency's safety concerns [26]. That withdrawal is neither a Category 1 placement nor permission to compound. Sections 503A and 503B impose separate requirements on the substance and its preparation [26]. A patient-specific prescribing decision and the PCAC advisory process each answer a different question from a final FDA listing decision [26][27].
This is the wall label. A patient-specific prescription does not turn TB-500 into an FDA-approved drug or add clinical-trial evidence for the fragment.
How to read the rest
The /research page walks the published evidence in roughly chronological order, from the 1992 actin-sequestration biochemistry through the 2025 hydrogel-delivery work [1][20]. The /dosage page summarizes the doses and routes used in the published animal and human studies and is explicit that no clinical dosing protocol exists for the fragment [22]. The /faq page answers the questions readers actually arrive with, including the WADA and athlete-sanction question [26]. The /references page lists every citation with DOI and PubMed or PMC link.
The whole site reads in one direction: from the research record outward to the regulatory record, then to the practical question of what TB-500 prescribed means in 2026. The phrase now needs two labels: prescription access for an individual patient, and a compounded drug with no FDA approval.