Key takeaways

TB-500 is a 7-amino-acid fragment (residues 17-23) of the larger 43-residue thymosin beta-4 protein.
The clinical trials that exist used full-length Tβ4 (RegeneRx programme), not the truncated TB-500 fragment sold in research-chemical channels.
Preclinical animal data supports cardiac, corneal, and dermal repair effects — most relevant to full-length Tβ4.
Identity confusion is a common problem — products sold as TB-500 are not the molecule that has been studied in published human trials.
UK: no approval, sold research-only. WADA-prohibited at all times for athletes.

What it is

TB-500 is a synthetic 7-amino-acid peptide (acetyl-LKKTETQ) corresponding to residues 17-23 of the 43-residue protein thymosin beta-4 (Tβ4). The label "TB-500" originated in animal-doping contexts in the early 2000s and subsequently spread through performance and recovery markets.

A genuine pharmaceutical programme around full-length Tβ4 — branded RGN-352, RGN-137, etc. — was conducted by RegeneRx Biopharmaceuticals in the 2010s for cardiac, corneal, and dermal applications. These trials used full-length Tβ4, not the TB-500 fragment. Marketing material that conflates the two is making a category error: clinical trial evidence for full-length Tβ4 does not directly transfer to TB-500.

How it works

Full-length Tβ4 is a major actin-sequestering protein involved in cell migration, angiogenesis, and tissue repair. Whether the 7-residue TB-500 fragment recapitulates these effects in vivo is biologically plausible but not well established.

Step 1

Subcutaneous injection

Most commonly cited route; sometimes IM.

Step 2

Tissue distribution

Hypothesised migration to sites of injury.

Step 3

Actin sequestration

Mechanism of full-length Tβ4; fragment activity uncertain.

Step 4

Repair signalling

Angiogenesis, fibroblast migration in preclinical models.

Benefits

Tissue repair (low confidence)

Preclinical evidence — primarily for full-length Tβ4 — supports accelerated wound healing in skin, cornea, and myocardium. RegeneRx phase-2 trials in dry eye disease and pressure ulcers showed mixed efficacy. None of the published clinical evidence used the TB-500 fragment.

Cardiac repair (low confidence — full-length Tβ4 only)

A small post-MI phase-2 trial of full-length Tβ4 (n=21) reported safety and feasibility but did not establish efficacy. Programme did not advance to phase-3.

Identity and evidence concerns

The fragment sold as "TB-500" has not itself been the subject of a published human clinical trial. Claims about TB-500 frequently extrapolate from full-length Tβ4 evidence, which is methodologically unsound. We treat the underlying mechanism as plausible but the human evidence specifically for the fragment as essentially absent.

Research summary

Thymosin beta-4 in chronic dry eye: phase-2 (full-length Tβ4)

2013

Phase-2 RCT, ophthalmic·n = 72

Topical full-length Tβ4 produced symptomatic improvement vs vehicle. Mechanism distinct from systemic TB-500 fragment use.

Cornea · 32(11):1450-1456

Thymosin beta-4 for myocardial infarction recovery (phase-2)

2014

Phase-2 safety / feasibility·n = 21

Full-length Tβ4 administered post-MI was safe and feasible. Efficacy signal modest; programme did not advance to phase-3.

Eur Heart J · 35(suppl)

Thymosin beta-4 fragment LKKTETQ (TB-500) in mouse wound model

2008

Animal study·n = Mice

Truncated fragment retained partial wound-healing activity vs full-length molecule in mouse dorsal wound model. One of few studies on the fragment specifically.

Ann N Y Acad Sci · 1112:340-350

Dosage & administration

No regulatory dosing exists. Schedules below come from research-chemical channel literature; they are not based on regulatory or trial protocols.

Source: research-chemical channel literature. No clinical trial protocol corresponds.
Phase	Dose	Duration	Notes
Loading	2.0–2.5 mg / week	4–6 weeks	Split twice weekly
Maintenance	2.0 mg / month	Ongoing	Reduced frequency

Side effects & safety

No serious safety signals in available data. Acute tolerance generally good. Long-term human safety is genuinely unknown.

Effect	Frequency	Severity
Injection-site reaction	5–10%	Mild
Lethargy / fatigue (acute)	~10%	Transient
Headache	Rare	Mild
Long-term effects	Unstudied	Unknown
Tumour-related concerns	Theoretical	Mechanism-based

Contraindications: Active malignancy (theoretical). Pregnancy. Concurrent immunosuppressants.

UK legal status

Research-use only — WADA-prohibited

TB-500 has no marketing authorisation anywhere as of May 2026. Sold as a research chemical only — not regulated for human use. WADA prohibits "growth factors and growth-factor modulators" at all times for competitive athletes; TB-500 falls within this category and has been the basis of multiple anti-doping sanctions in racing and combat sports. Supply for human use without prescription is illegal under the Human Medicines Regulations 2012.

Summary

TB-500 is the most identity-confused peptide we cover. The clinical evidence on full-length thymosin beta-4 — modest as it is — does not transfer to the truncated fragment commonly sold under this name. Mechanism is plausible; safety appears acceptable in limited data; human efficacy specifically for the fragment is essentially unstudied. UK readers considering recovery peptides should be aware of both the identity confusion and the WADA implications for competitive athletes.

References (5)

Sosne G, et al. Thymosin beta-4 promotes corneal wound healing: phase-2 trial. Cornea. 2013;32(11):1450-1456.
Crockford D, et al. Thymosin beta-4 in cardiac repair: clinical experience to date. Ann N Y Acad Sci. 2010;1194:179-189.
Kim S, et al. Thymosin beta-4 fragment LKKTETQ retains wound-healing activity. Ann N Y Acad Sci. 2008;1112:340-350.
World Anti-Doping Agency. Prohibited List 2026. S2: Peptide Hormones, Growth Factors. WADA, Montreal.
MHRA. Note: TB-500 / thymosin beta-4 has no UK marketing authorisation as of May 2026.

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