TB-500

TB-500 is a grey-market label that does two things at once. It refers to a synthetic heptapeptide (AC-LKKTETQ, CAS 885340-08-9) corresponding to amino acids 17 to 23 of thymosin beta-4, and it is also routinely used as a colloquial name for full-length thymosin beta-4 itself (Tβ4, a 43-residue acetylated peptide first isolated from calf thymus by Allan Goldstein and colleagues in the 1960s, with the complete sequence reported by Low, Hu and Goldstein in 1981). The published academic literature speaks of thymosin beta-4 or Tβ4. The grey-market literature, vendor pages and athletic-community discussion speak of TB-500. Anyone reading the literature alongside the marketing should know the two names are not strictly interchangeable, and that the published trial work has used the full-length peptide.

The preclinical evidence base is real. Tβ4 functions as the major G-actin sequestering molecule in eukaryotic cells, controlling the available pool of monomeric actin and therefore the cytoskeletal machinery for cell migration, angiogenesis and tissue remodelling. Reviews by Goldstein, Hannappel and Kleinman (2005), Philp and Kleinman (2010), Crockford and colleagues (2010), Dubé and colleagues (2012), Bollini, Riley and Smart (2015), and Bjorklund and colleagues (2020) summarise rodent and large-animal data across dermal wound healing, corneal repair, cardiac protection after myocardial infarction, and neurological injury. The mechanistic story across these reviews is consistent: angiogenic activity, anti-inflammatory cytokine modulation, recruitment of progenitor cells, and accelerated re-epithelialisation in injured tissue.

Human clinical data outside the eye is essentially absent. There is no published Phase 2 or Phase 3 randomised controlled trial of systemic TB-500 or thymosin beta-4 for tendon, ligament, muscle, cardiac or general injury-recovery indications. The Treadwell and colleagues (2012) paper reports preliminary acceleration of dermal wound healing in patients, but the Phase 2 and Phase 3 trial programme that would establish a defensible efficacy or safety case in soft-tissue injury has not been completed. Anything quoted online as a typical TB-500 protocol for tendon repair, including the often-cited 2 to 2.5 mg twice-weekly loading and 2 mg weekly maintenance pattern, is community-derived rather than trial-validated.

The exception is ophthalmology. RegeneRx Biopharmaceuticals and its ReGenTree joint venture (with HLB Therapeutics, formerly GtreeBNT) have run multiple human trials of RGN-259, a 0.1% Tβ4 ophthalmic solution. The 2023 Phase 3 trial in neurotrophic keratopathy (Sosne, Kleinman, Springs, Gross, Sung and Kang, Int J Mol Sci 2023, PMID 36613994) randomised 18 patients with stage 2 to 3 persistent epithelial defects to RGN-259 or placebo and reported complete healing at four weeks in 6 of 10 treated patients versus 1 of 8 on placebo, with a sustained advantage at day 43 and improvements in ocular discomfort, foreign body sensation and dryness. The ARISE programme has run two completed Phase 3 trials and a third in progress for dry eye disease, with overall enrolment across the programme reported by the sponsor as approximately 1,600 patients. This is the only place in the published literature where TB-500 (in the form of full-length Tβ4) has produced positive Western-standard trial data, and it is a topical formulation, not an injection.

In our coverage area, TB-500 has no marketing authorisation. The EMA medicines register returns no result for thymosin beta-4, TB-500, RGN-259 or timbetasin (the WHO-assigned international non-proprietary name for Tβ4). The MHRA has not licensed it in the UK. The FDA has not approved it; in September 2023 thymosin beta-4 was placed in Category 2 of the 503A bulks list, the designation that effectively prohibits compounding pharmacies from preparing it, and it was never previously in Category 1. The Pharmacy Compounding Advisory Committee is scheduled to revisit TB-500 (both free base and acetate forms) at its 23 to 24 July 2026 meeting, alongside BPC-157, KPV, MOTS-c, Emideltide (DSIP), Epitalon and Semax. Australia and New Zealand classify TB-500 differently: the Therapeutic Goods Administration added thymosin beta-4 and TB-500 to Schedule 4 (prescription-only medicine) in 2016, but that is a national scheduling decision, not a marketing authorisation.

The athletic-doping picture is settled. USADA's 2018 prohibited list summary records that thymosin-β4 and its derivatives, e.g. TB-500, were added as examples of prohibited growth factors under section S2.3 of the WADA Prohibited List, with effect from 1 January 2018. The substance is prohibited in and out of competition and is treated as a non-Specified Substance under the Code. WADA's scientific-research programme has commissioned dedicated detection work on TB-500 metabolism in urine and plasma, which is the operational sign that anti-doping laboratories are actively testing for it. A Canadian athlete received a four-year ineligibility period for using BPC-157 and TB-500 together, illustrating how the sanction picture plays out in practice. The US Department of Defense's Operation Supplement Safety programme names TB-500 alongside BPC-157 as an unapproved drug prohibited for service members.

The grey-market supply reality has the usual implications, with one extra wrinkle. Most vendors sell vials labelled TB-500 5 mg, but the molecule actually inside the vial can be either the AC-LKKTETQ heptapeptide or the full-length 43-residue Tβ4, depending on the vendor and the batch, and the label often does not specify. The two molecules have different molecular weights (the heptapeptide is around 889 daltons; full-length Tβ4 is around 4,963 daltons) and behave differently in any mass-spectrometry identity check, so identity testing matters more here than it does for a peptide with only one canonical form. Independent purity testing of grey-market injury-recovery peptides routinely identifies failures on purity, identity and contamination; we do not have a TB-500-specific independent testing dataset of the rigor a reader could rely on. The Practical considerations section below lists the verifiable quality signals that apply across this product class.

This page is for education and journalism. We do not advise on starting, stopping, dosing, or sourcing TB-500, and we do not facilitate the sale of any peptide. The conversation about whether to consider TB-500 belongs with a clinician who knows your medical history. Use the country pages at /regulation/[country]/tb500 for the jurisdiction-specific picture, the Practical considerations section for the operational reality of grey-market supply, and the source list below to read the preclinical reviews, the RegeneRx ophthalmic trial publications, and the primary regulatory documents in full.