Thymosin β4 N-terminal fragment (synthetic)
TB-500
17-amino-acid synthetic fragment (LKKTETQEKNPLPSKETI) corresponding to the actin-binding N-terminal region of thymosin β4
Overview
Before anything else about this compound, the identity question needs to be settled: TB-500 is not thymosin β4. It is a synthetic 17-amino-acid fragment (LKKTETQEKNPLPSKETI) corresponding to the N-terminal actin-binding region of the parent 43-amino-acid Tβ4 protein. Popular sources — including many that present themselves as authoritative — treat 'TB-500' and 'thymosin β4' as interchangeable names. They are not. The distinction has real consequences for how the evidence base should be read.
Thymosin β4 is an endogenous protein present in essentially every mammalian cell, first isolated from calf thymus in the 1980s. Its actin-sequestering role — binding G-actin monomers and modulating their availability for polymerisation — is one of the most-cited functions of the peptide. Beginning in the 2000s, RegeneRx Biopharmaceuticals developed the intact Tβ4 protein through phase-1 and phase-2 human trials for cardiac repair after myocardial infarction, chronic wound healing, and corneal defects. Those trials produced real human safety data and modest efficacy signals across several indications. That evidence base belongs to Tβ4, not to TB-500.
TB-500 as an identifiable product emerged from a different context: equine veterinary medicine. The 17-amino-acid fragment was marketed as an intramuscular anti-inflammatory and tissue-repair injection for racing horses recovering from soft-tissue injuries. When multiple racing authorities and the World Anti-Doping Agency added it to their prohibited lists in the 2010s, the veterinary market largely receded. What remained is a compound with a research-supply presence, no completed human trial of the fragment specifically, and a popular reputation that borrows heavily from the parent Tβ4 literature.
This does not mean TB-500 is a scam or that its proposed mechanism is nonsense. The actin-binding region is the mechanistically active part of Tβ4 for cell migration and cytoskeleton modulation, and the argument that the fragment alone can produce a subset of the parent protein's effects is biologically defensible. It means that when someone cites 'the phase-1 safety data for TB-500,' the honest reading is that they are almost certainly quoting Tβ4 data. Understanding the difference is what allows an informed reading of the compound.
Quick Facts & Evidence
- Category
- Thymosin β4 N-terminal fragment (synthetic)
- Research area
- Tissue repair peptide
- Most studied for
- Tendon and ligament healing (preclinical, largely via Tβ4 studies)
- Wound-healing acceleration (Malinda 1999, Tβ4)
- Cardiac repair after myocardial infarction (Tβ4 phase 1/2 through RegeneRx)
- Equine racehorse recovery (historical veterinary use, now prohibited by racing authorities)
- Clinical status
- Research use only — no approved clinical indication
- Human evidence
- Early Human Evidence
- Regulatory status
- Not approved by FDA, EMA or MHRA
Early Human Evidence
Small-scale human studies, observational data, or off-label case reports only. Substantial uncertainty remains.
Research Protocols
Research Protocol Snapshot
Preparation covered on this page
Freeze-dried injectable research format
This page covers the RUO lyophilized TB-500 vial reconstituted with bacteriostatic water for subcutaneous research use, following the standard Healthy Mango preparation convention.
TB-500 research values at a glance.
| Item | Example value |
|---|---|
| Vial size | 10 mg |
| Liquid used to mix | Bacteriostatic water |
| Amount of liquid added | 2.0 mL |
| Final concentration | 5 mg/mL |
| How it's given | Subcutaneous injection |
| Loading dose | 2.5–5 mg twice weekly (weeks 1–4 through 4–6) |
| Maintenance dose | 2.5 mg, 1–2× per week after loading |
| Duration | Injury-driven; stop when the injury has resolved |
Reported Dosing
The practitioner-reference research protocol for TB-500 is a two-phase pattern: a loading phase of 2.5–5 mg twice weekly for 4–6 weeks, followed by a maintenance phase of 2.5 mg once or twice weekly for as long as the injury requires. It is educational reference, not a recommendation.
The Reported Protocol
| Dose | Frequency | Duration | Notes |
|---|---|---|---|
| 2.5–5 mg | Twice weekly, subcutaneous | Loading phase, 4–6 weeks | 0.5–1.0 mL at 5 mg/mL |
| 2.5 mg | 1–2× per week, subcutaneous | Maintenance until the injury has resolved | 0.5 mL at 5 mg/mL |
Why protocols vary
TB-500's mechanism is actin-cytoskeleton regulation for cell migration and recruitment; that pharmacology builds effect over weeks rather than acting on a single dose. The loading phase produces the plasma-tissue accumulation the compound is designed around; skipping it, per the practitioner reference, runs the compound at a fraction of its intended effect.
The maintenance phase steps down once the loading target has been reached, matching cadence to the residual repair need rather than a fixed calendar.
Preparing the Solution
Turning the freeze-dried powder into a measurable liquid.
Documented preparation
The documented research protocol is based on this preparation concentration.
Freeze-dried powder: 10 mg vial
Diluent: 2.0 mL bacteriostatic water
Final concentration: 5 mg/mL
Vial and volume from the practitioner reference; concentration calculated · Research-practitioner guide
Your vial
Matching preparation
Bacteriostatic water
2mL
Resulting concentration
5 mg/mL
Equivalent volume
The reported research amount of 2.5–5 mg is contained within
0.5–1.0mL
of the prepared solution now in your vial.
Show calculation
- Documented concentration
- 10 mg ÷ 2 mL = 5 mg/mL
- Bacteriostatic water to match the documented concentration
- 10 mg ÷ 5 mg/mL = 2 mL
- Equivalent volume at this concentration
- 2.5–5 mg ÷ 5 mg/mL = 0.5–1 mL
This tool performs arithmetic conversions using the preparation example and reported research amount shown on this page. It does not recommend an amount, route, preparation method, or use.
This tool performs arithmetic conversions using the preparation example and reported research amount shown on this page. It does not recommend an amount, route, preparation method, or use.Sources for these values
- Documented in the practitioner referenceResearch-practitioner guide
This example explains how concentration and volume are calculated for the standard RUO preparation. It is not a preparation guide.
How It's Given
Method used for this format
Subcutaneous injection, twice weekly (loading) then 1–2× weekly (maintenance)
Documented in the practitioner reference · Research-practitioner guide
Why this method
TB-500 is a 17-amino-acid peptide fragment; the subcutaneous route delivers it into circulation without the gastrointestinal degradation that would break the molecule down.
Systemic subcutaneous dosing is used because the mechanism relies on cell-migration signalling to reach injury sites throughout the body, not on a localised depot.
Injection sites reported
- Abdomen (rotate sites)
- Front of the thigh
- Back of the upper arm
- Avoid scarred, bruised, inflamed, or infected skin
Storage
Before mixing
- Refrigerate 2–8 °C
- Protect from light
- Do not freeze
General RUO practice · Research-practitioner guide
After mixing
- Refrigerate 2–8 °C
- Use within 7–10 days
- Do not freeze
- Discard if cloudy or discoloured
General RUO practice · Research-practitioner guide
Handling
- Direct diluent slowly down the vial wall
- Gently swirl until dissolved — do not shake
- New sterile needle each draw
- Do not share vials
General RUO practice · Research-practitioner guide
Storage guidance summarises standard RUO peptide handling. TB-500 (the 17-amino-acid fragment) is separately WADA-prohibited in athletes; check the specific vial's supplied instructions before use.
Common Cycle
The practitioner reference frames TB-500 as injury-driven — 4–6 weeks of loading followed by maintenance for as long as the injury needs support. It is not a calendar-fixed cycle.
- Cycle Length
- 4–6 week loading phase + injury-driven maintenance
- Break Before the Next Cycle
- Not calendar-cycled; stop when the injury has resolved
- What the Research Shows
- No large controlled follow-up trial of the fragment specifically exists; parent Tβ4 trials ran ≤6 months
Documented in the practitioner reference · Research-practitioner guide
Published human trials of the intact Tβ4 protein (RegeneRx phase-1/2) are not the same as trials of the 17-amino-acid TB-500 fragment.
Compound Overview
Current areas of research
The following are effects reported in preclinical research and (for the parent Tβ4 protein) in limited human phase-1/2 data. The TB-500 fragment specifically has not been characterised in a controlled human trial.
- Actin cytoskeleton modulation and cell-migration effects (mechanistic, via parent Tβ4)
- Wound-healing acceleration in animal models (Malinda 1999, in Tβ4)
- Cardiac cell migration and modest repair signals in myocardial infarction models (Tβ4 phase 1/2)
- Corneal defect and ophthalmic wound-healing indications (Tβ4 phase 1/2)
- Historical equine soft-tissue injury recovery (veterinary use, now prohibited by racing authorities)
Mechanism of action
Before anything else about this compound, the identity question needs to be settled: TB-500 is not thymosin β4. It is a synthetic 17-amino-acid fragment (LKKTETQEKNPLPSKETI) corresponding to the N-terminal actin-binding region of the parent 43-amino-acid Tβ4 protein. Popular sources — including many that present themselves as authoritative — treat 'TB-500' and 'thymosin β4' as interchangeable names. They are not. The distinction has real consequences for how the evidence base should be read.
Thymosin β4 is an endogenous protein present in essentially every mammalian cell, first isolated from calf thymus in the 1980s. Its actin-sequestering role — binding G-actin monomers and modulating their availability for polymerisation — is one of the most-cited functions of the peptide. Beginning in the 2000s, RegeneRx Biopharmaceuticals developed the intact Tβ4 protein through phase-1 and phase-2 human trials for cardiac repair after myocardial infarction, chronic wound healing, and corneal defects. Those trials produced real human safety data and modest efficacy signals across several indications. That evidence base belongs to Tβ4, not to TB-500.
TB-500 as an identifiable product emerged from a different context: equine veterinary medicine. The 17-amino-acid fragment was marketed as an intramuscular anti-inflammatory and tissue-repair injection for racing horses recovering from soft-tissue injuries. When multiple racing authorities and the World Anti-Doping Agency added it to their prohibited lists in the 2010s, the veterinary market largely receded. What remained is a compound with a research-supply presence, no completed human trial of the fragment specifically, and a popular reputation that borrows heavily from the parent Tβ4 literature.
This does not mean TB-500 is a scam or that its proposed mechanism is nonsense. The actin-binding region is the mechanistically active part of Tβ4 for cell migration and cytoskeleton modulation, and the argument that the fragment alone can produce a subset of the parent protein's effects is biologically defensible. It means that when someone cites 'the phase-1 safety data for TB-500,' the honest reading is that they are almost certainly quoting Tβ4 data. Understanding the difference is what allows an informed reading of the compound.
- TB-500 is NOT thymosin β4 — it is a 17-amino-acid synthetic fragment of the 43-amino-acid parent protein
- The impressive Tβ4 human evidence base (RegeneRx phase-1/2 in cardiac, wound, and corneal indications) does not automatically transfer to the TB-500 fragment
- Originated in equine veterinary medicine; now on the WADA prohibited list under S2 (peptide hormones and growth factors)
Human research
Reading the TB-500 evidence base requires holding two categories separate: what has been characterised for the parent thymosin β4 protein (substantial), and what has been characterised for the TB-500 fragment specifically (essentially nothing at the human clinical trial level). Most popular sources merge these categories, which is what allows the fragment to inherit the parent protein's clinical credibility without earning it.
The parent Tβ4 literature is anchored by Goldstein's foundational work (originally isolating the protein from calf thymus in the 1980s, and Goldstein Trends Mol Med 2005 for the modern mechanistic framing). Malinda 1999 in J Invest Dermatol demonstrated wound-healing acceleration in animal models. Crockford 2010 in Ann NY Acad Sci is the consolidating review of RegeneRx-era phase-1/2 human development across cardiac, wound, and corneal indications. Ruff 2010 characterises the phase-1 safety profile at IV doses up to 1260 mg.
For the TB-500 fragment specifically, the published record is largely restricted to preclinical mechanistic studies confirming that the actin-binding N-terminal region alone recapitulates a subset of parent-protein effects on cell migration in vitro. There is no controlled human dose-response trial, no phase-2 randomised trial, and no post-marketing surveillance dataset. The Chang 2011 tendon-cell study cited elsewhere on Healthy Mango is a BPC-157 paper, not a TB-500 paper — another common source of literature-navigation confusion.
Goldstein Trends Mol Med 2005
Consolidating review of thymosin β4's actin-sequestering role and tissue-repair effects. Foundational for understanding the parent protein — from which TB-500 is derived — but not TB-500-specific evidence.
Malinda J Invest Dermatol 1999
Preclinical demonstration that thymosin β4 accelerates dermal wound healing in animal models. The mechanistic foundation for the parent-protein wound-healing indications later pursued through RegeneRx. Again, Tβ4-specific evidence, not TB-500-specific.
Crockford Ann NY Acad Sci 2010
Consolidating review of the RegeneRx-era Tβ4 phase-1/2 human development program: cardiac repair after MI, chronic wound healing, corneal defects. Human trial data — but for the full-length 43-amino-acid protein, not the 17-amino-acid TB-500 fragment.
Ruff Ann NY Acad Sci 2010
Preclinical safety assessment supporting the Tβ4 phase-1 program at IV doses up to 1260 mg. The safety profile most commonly cited in TB-500 discussions belongs to this Tβ4 paper — a different molecule at a different dose range and route.
TB-500 has never had FDA approval for human use, has never completed a phase-1 or phase-2 randomised human trial of the fragment specifically, and has never been an active pharmaceutical development program under any human-medicine sponsor. That regulatory position needs to be stated clearly because the compound's popular reputation borrows so heavily from the parent Tβ4 protein's more substantive record.
The parent thymosin β4 (43-amino-acid protein) HAS had phase-1 and phase-2 human development, primarily through RegeneRx Biopharmaceuticals starting in the mid-2000s. Indications included cardiac repair after myocardial infarction, chronic non-healing wounds, and corneal defects. Those programs produced safety data and modest efficacy signals but did not culminate in FDA approval, and RegeneRx's active development has substantially wound down. That evidence base is characterised in Crockford 2010 and Ruff 2010 — and it is a Tβ4 evidence base, not a TB-500 evidence base.
TB-500's identifiable history is in equine veterinary medicine. It was marketed and used as an anti-inflammatory / soft-tissue-repair injection for racing horses through the 2000s and early 2010s. When racing authorities and WADA formalised it as prohibited, the veterinary market receded significantly. What remains is a compound available through research-supply and compounding channels, with a popular human-use reputation that outruns its actual human evidence base.
Safety considerations
Human tolerability data for the TB-500 fragment specifically are essentially absent. The following draws on parent-Tβ4 phase-1 tolerability (Ruff 2010) and research-context observation.
- Injection-site reactions
- Parent Tβ4 IV phase-1 tolerability generally good (Ruff 2010) — But this is not TB-500-specific data
- Long-term safety of the TB-500 fragment in humans is uncharacterised — No post-marketing surveillance dataset exists — the fragment has not been marketed for human use
- Theoretical cell-migration considerations — A compound that modulates cell migration warrants caution in oncology contexts
There is no approved-label list of contraindications for human use because there is no approved human indication. The considerations below draw on the compound's mechanistic profile and its specific regulatory-and-athletic context.
- Active or recent malignancy — theoretical caution given cell-migration and actin-modulation effects
- Pregnancy and breastfeeding — no human safety data
- Known hypersensitivity to the compound or excipients
- Competitive athletes: TB-500 is on the WADA prohibited list (S2 category, peptide hormones and growth factors) — a positive test carries the standard doping sanctions
- Concurrent use with anti-migration or anti-metastatic cancer therapies is mechanistically counter-directional
Monitoring
- Injection-site reactions across rotation sites
- Response within a defined recovery window rather than open-ended use
- Any new symptoms suggesting hypersensitivity or unexpected inflammation
Frequently asked questions
Is TB-500 the same as thymosin β4?
No, and this is the single most important thing to understand about the compound. Thymosin β4 is a 43-amino-acid endogenous protein with real preclinical and (limited) human clinical trial data, primarily through RegeneRx. TB-500 is a 17-amino-acid synthetic fragment corresponding to Tβ4's actin-binding N-terminal region. The fragment shares an important active region but is not the same molecule. Popular sources that cite 'Ruff 2010 safety data for TB-500' are almost always quoting Tβ4 data — same laboratory family, different molecule.
If Tβ4 had real human trials, does that mean TB-500 is safe?
It means something, but less than it seems. The parent Tβ4 phase-1 program (Ruff 2010) characterised safety at IV doses up to 1260 mg for the full-length protein. The TB-500 fragment is a different molecule at a different dose range and a different route (typically 2–5 mg subcutaneous). Extrapolating safety from parent to fragment is defensible mechanistically but is not the same as having actually characterised the fragment in humans. If safety is the primary concern, the honest framing is that TB-500-specific human safety data is essentially absent.
Why is TB-500 mostly found through veterinary suppliers?
Because equine veterinary medicine was the original identifiable use of the compound. Racing-horse recovery from soft-tissue injuries was where TB-500 as a marketed product first appeared, with intramuscular loading protocols used across the racing industry through the 2000s and early 2010s. When racing authorities and WADA formalised TB-500 as prohibited, the veterinary market largely receded, but the supply-chain memory of that origin persists.
How does TB-500 compare to BPC-157?
They are frequently discussed together but come from entirely different origins. BPC-157 is a 15-amino-acid fragment from a human gastric-juice protein, with its evidence base concentrated in the Sikiric laboratory. TB-500 is a 17-amino-acid fragment of thymosin β4, with its evidence base largely borrowed from the parent Tβ4 protein's more substantive human trial record. Their mechanisms are distinct: BPC-157 works largely through proposed VEGF and NO-system pathways; TB-500 works through actin cytoskeleton modulation. See the BPC-157 vs TB-500 comparison for a structured contrast.
What is TB-500's regulatory and anti-doping status?
Not FDA-approved for human use. Not EMA-authorised. On the WADA prohibited list under the S2 category (peptide hormones, growth factors, and related substances). Prohibited under most major racing-authority anti-doping rules. For competitive athletes in any sport under WADA jurisdiction, a positive test carries the standard doping sanctions regardless of intent.
References
- [1]
Thymosin beta 4: actin-sequestering protein moonlights to repair injured tissues — Goldstein AL, Hannappel E, Kleinman HK, Trends in Molecular Medicine (2005)
- [2]
Thymosin beta4 accelerates wound healing — Malinda KM, Sidhu GS, Mani H, et al., Journal of Investigative Dermatology (1999)
- [3]
Thymosin beta4: structure, function, and biological properties supporting current and future clinical applications — Crockford D, Turjman N, Allan C, Angel J, Annals of the New York Academy of Sciences (2010)
- [4]
Preclinical safety assessment of Thymosin β4 for the treatment of patients with damaged heart tissue — Ruff D, Crockford D, Girardi G, Zhang Y, Annals of the New York Academy of Sciences (2010)
- [5]
World Anti-Doping Agency (WADA) Prohibited List — S2 peptide hormones, growth factors, related substances, and mimetics — World Anti-Doping Agency (2024)
- [6]
Peptides & Compounds — The No-Jargon Guide (v5) — Healthy Mango Editorial, Healthy Mango practitioner reference (2026)
Laboratory Reference Notice
This section summarizes procedures and study parameters reported in published scientific literature and laboratory protocols. It is provided for educational and research reference only and must not be interpreted as medical advice, clinical guidance, or instructions for personal use.
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