Is TB-500 a prescription drug? The wall label, not the marketing copy.

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. As of September 2023, a U.S. compounding pharmacy cannot legally make TB-500 for a patient; the FDA placed it in Category 2 of the interim 503A Bulks List, meaning significant safety concerns. WADA classifies it as prohibited for competitive athletes. The name on this domain uses prescribed the way a museum uses an empty plinth — to mark a category that does not yet exist, not to claim the object is there. 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. The whole site exists to do one thing carefully: explain what the published Thymosin Beta-4 record actually says about a compound whose marketed name carries the word prescribed as if a prescription were available.

A prescription is not available. 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 September 2023 compounding decision, 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 — as one of its safety concerns when it restricted TB-500 from compounding ^[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].

Why nobody can write a prescription

Prescriptions exist for approved drugs. They also exist, in the off-label sense, for unapproved indications of approved drugs. They do not exist for substances with no approved product anywhere in the regulatory record.

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. There is therefore no on-label prescription, and because off-label prescribing requires an approved product as the starting point, there is no off-label path either.

Until September 2023, a parallel route remained open in the United States: a state-licensed compounding pharmacy operating under Section 503A could prepare TB-500 for a patient if the substance was on the FDA's 503A Bulks List. On September 29, 2023, the FDA placed Thymosin Beta-4, Fragment (LKKTETQ) — TB-500 by its chemical identity — in Category 2 of the Interim 503A Bulks List, the bin for substances the agency has determined raise significant safety concerns and that may not be used in compounding while under review ^[26]. The same placement effectively closed the Section 503B outsourcing-facility route. As of 2025, TB-500 remains in Category 2; it was not among the substances voted on at the October or December 2024 Pharmacy Compounding Advisory Committee meetings, which considered a different group of peptides ^[27].

This is the wall label. The site's name uses the word prescribed the way a museum places an empty plinth: as a position relative to the absent object, not a claim that the object is there.

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 answer is that it means almost nothing, because the noun phrase does not yet refer to anything the United States regulatory system has accepted.