Accelerated dermal wound healing (pre-clinical and human topical) [1][2]
Thymosin β4 accelerates wound closure, keratinocyte migration and angiogenesis across animal models, with human clinical evaluation in topical wound and ophthalmic settings.
PrecisePep/Peptide Library/TB-500
Regenerative & Tissue Repair
TB-500
Thymosin β4 fragment · Tβ4 (17–23) acetylated fragment · TB4-Frag
A synthetic fragment marketed as thymosin beta-4 — actin-binding, cell-migration-promoting, anti-fibrotic in pre-clinical work, and routinely conflated with the full-length parent peptide that actually carries the clinical data.
00 Overview
The first thing to be clear about is what TB-500 actually is. Thymosin β4 (Tβ4) is a naturally occurring 43-amino-acid protein, one of the most abundant intracellular peptides in human tissue, and the molecule that carries essentially all of the credible research — including registered human trials for dry eye, corneal wound healing and cardiac repair.[1][4] "TB-500" is a research-chemical product, generally a short synthetic fragment centred on the LKKTETQ actin-binding motif, sold on the premise that the fragment reproduces the parent's activity.
That premise is partially supported: the actin-binding heptapeptide does retain measurable activity in pre-clinical models. But the parent protein has functions the fragment cannot have, and the two are not interchangeable. Vendor material labelled "TB-500" may be the fragment, may be full-length Tβ4, and may be neither — this is one of the least standardised products in the research-peptide market.
The pre-clinical case for Tβ4 is genuinely broad: accelerated dermal and corneal wound healing, cardiac repair after infarction, reduced fibrosis, neurological recovery, and hair-follicle effects.[2][3] Human trials exist for topical and ophthalmic use. There is no human trial evidence for subcutaneous TB-500 in musculoskeletal injury — which is what essentially all real-world use is for.
Fragment ≠ parent molecule
When a claim on this page is sourced to thymosin β4 research, that means the 43-residue protein. Whether a 7-residue fragment sold as TB-500 reproduces that effect at the doses used is an assumption, not a finding. Read every "study" entry below with that substitution in mind.
// Mechanism of action
G-actin sequestration. Thymosin β4 is the principal intracellular G-actin sequestering protein. By binding monomeric actin it regulates the pool available for filament assembly, which governs cytoskeletal remodelling — and therefore the ability of a cell to change shape and move. The LKKTETQ motif is the functional core of this activity and the basis of the TB-500 fragment.
Cell migration. Downstream of actin regulation, Tβ4 promotes migration of endothelial cells, keratinocytes and progenitor populations toward injury. This is why the effect is described as systemic: unlike a locally acting growth factor, it changes the capacity of repair cells to travel to wherever the damage is.
Angiogenesis. Tβ4 promotes endothelial cell migration, tube formation and vessel growth, and upregulates VEGF signalling — mechanistically overlapping with BPC-157 while arriving there by a different route.
Anti-fibrotic and anti-inflammatory activity. Reported downregulation of pro-fibrotic signalling and of inflammatory cytokine production, with reduced scar formation in cardiac and dermal models. The anti-fibrotic property is the most distinctive claim attached to the molecule, and the one most relevant to the community interest in scar tissue and chronic injury.
Stem and progenitor cell activation. Reported activation of epicardial progenitor cells in cardiac models and of hair-follicle stem cells in dermal models.
01 Reported benefits
Effects that have been reported. A study-tier entry means a result was published — not that the effect is established, reproducible, or transferable from a rodent to a person.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Corneal wound healing and dry eye (human trials) [4]
Full-length Tβ4 (as RGN-259) has been evaluated in registered human trials for neurotrophic keratopathy and dry-eye disease — the strongest human evidence in the thymosin β4 space, and topical rather than systemic.
Cardiac repair after ischaemic injury (animal) [2][3]
Reported reduction in infarct size, activation of epicardial progenitors, improved cardiac function and reduced fibrosis in rodent and porcine myocardial infarction models.
Long-term dosing outperformed short-term dosing (rodent chronic ischaemia) [6][7]
The most directly relevant study to the question of how long to run this. In a rat model of chronic myocardial ischaemia, Tβ4 was given on two schedules: short-term (the first three days after injury only) and long-term (the first three days plus every third day to the end of the study). The long-term arm reduced infarct size and significantly improved haemodynamic performance; the short-term arm only tended toward the same. That is a genuine head-to-head favouring sustained dosing in a chronic condition, and it is the strongest published support for running this compound long rather than short. Set against it: systemic Tβ4 given before and after ischaemia failed to attenuate ischaemia-reperfusion injury in pigs — so the effect did not carry from rodent to large animal, which is the step that matters most.
Reduced fibrosis and scar formation [2][3]
Anti-fibrotic effects reported across cardiac, hepatic, renal and dermal models — the most consistently replicated property of the parent peptide.
Repeated human dosing tolerated without accumulation (phase 1) [4]
Recombinant Tβ4 has been through phase 1 and phase 2 human testing under the RGN-352 and RGN-259 programmes. A phase 1 study in healthy volunteers reported that single and multiple intravenous doses were well tolerated, with no dose-limiting toxicities and no obvious drug accumulation on continuous administration. That is real human safety data and it is the most defensible part of the case for extended use. Note the limits: phase 1 measures tolerability rather than benefit, the exposure was weeks rather than years, and the route was intravenous rather than subcutaneous.
Neurological recovery in injury models [3]
Improved functional recovery reported in rodent traumatic brain injury, stroke and peripheral nerve models, associated with oligodendrogenesis and neuroplasticity.
Hair growth and follicle stem-cell activation (rodent) [2]
Reported activation of hair-follicle stem cells and accelerated follicle development in rodent models.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Systemic musculoskeletal repair in humans
The dominant use case and one with no human evidence. The reasoning — actin regulation enables repair-cell migration, so remote injuries benefit from systemic administration — is mechanistically clean and clinically undemonstrated.
Breakdown or remodelling of existing scar and adhesion tissue
Extrapolated from anti-fibrotic findings in acute injury models. Whether an anti-fibrotic signal can remodel established mature scar is a different question and one the literature does not answer.
Widespread myofascial pain in fibromyalgia
The proposal is that anti-inflammatory and tissue-repair signalling eases peripheral pain generators. The premise is the problem: fibromyalgia is a central pain disorder, tender points are not inflamed and inflammatory markers are typically normal. The rationale may hold for coexisting myofascial pain or tendinopathy — a narrower and more defensible claim.
Flexibility and range-of-motion improvement
A very common claim, resting on the anti-fibrotic mechanism. Not measured in any study.
Fragment activity equivalence to full-length Tβ4
The load-bearing assumption of the entire TB-500 market. The actin-binding motif is active in vitro; equivalence at the whole-organism level is assumed rather than shown.
Absence of reported tolerance — and what that does and does not mean [1][4]
As with BPC-157, it is often stated that Tβ4 causes no tachyphylaxis and can be run indefinitely. No study has tested for tachyphylaxis with this compound either. The nearest real evidence is the phase 1 finding above — no accumulation across repeated intravenous doses — which is a pharmacokinetic observation about clearance, not a demonstration that the tissue response is maintained over time. The rodent chronic-ischaemia result above is the better argument for sustained dosing, because it measured an outcome rather than a drug level. Neither establishes that daily administration indefinitely is either necessary or safe.
Concern: pro-angiogenic and pro-migratory signalling in malignancy [5]
Thymosin β4 overexpression has been associated with tumour progression and metastasis in oncology literature — cell migration is precisely what metastasis requires. This is the most substantive theoretical risk attached to the compound and it is rarely mentioned in community discussion.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Whole-body reduction in aches and stiffness
The characteristic community report, distinct from BPC-157: users describe a diffuse systemic effect rather than a localised one, which matches the systemic mechanism.
Improved range of motion in chronically stiff joints
Frequently attributed to the anti-fibrotic mechanism. Unmeasured and confounded by any concurrent mobility work.
Slower onset than BPC-157
Community consensus is that TB-500 takes two to four weeks to produce noticeable effect where BPC-157 is reported to act faster. Consistent with a systemic remodelling mechanism versus a local perfusion one.
Hair and skin quality changes
Occasionally reported, aligning with the follicle and dermal literature. Uncontrolled.
Head-rush or transient lightheadedness after injection
Reported with larger loading doses. Unverified; attributed to vasodilatory effects.
02 Adverse effects & risks
Adverse effects, contraindications and unknowns. The grey-market tier is where under-reporting is worst: uncontrolled use produces no systematic safety surveillance at all, so absence of a reported harm is not evidence of safety.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Favourable safety in human topical/ophthalmic trials [4]
Registered human trials of full-length Tβ4 in ophthalmic use reported good tolerability. This does not characterise repeated systemic subcutaneous administration in a healthy person.
Association between Tβ4 expression and tumour progression [5]
Oncology literature links elevated thymosin β4 expression to invasiveness and metastatic behaviour in several tumour types. This is an association in disease biology, not a demonstration that exogenous administration causes cancer — but it is the single most relevant safety literature that exists.
No systemic human safety data for the TB-500 fragment
No published pharmacokinetics, no chronic dosing study, no long-term follow-up. The safety profile is genuinely unknown rather than known-to-be-good.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Promotion of angiogenesis and migration in occult malignancy [5]
The theoretical concern follows directly from the mechanism and from the oncology association. Nobody using this compound is being screened for it.
Immunogenicity from fragment administration
Short synthetic fragments of endogenous proteins can raise antibodies that cross-react with the parent protein. Given how abundant Tβ4 is in human tissue, this is a non-trivial theoretical concern and has never been examined.
Unpredictable effects from unstandardised product
Because "TB-500" is not a defined chemical entity across suppliers, the risk profile is supplier-specific in a way that is unusual even for this market.
Anti-fibrotic activity where fibrosis is load-bearing
Scar tissue is sometimes structurally necessary. A systemic anti-fibrotic signal does not distinguish between adhesion and repair.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Fatigue and lethargy in the first days of loading
One of the more consistent community reports, typically at higher twice-weekly loading doses.
Injection-site reactions
Generally mild; more prominent in blends.
Head pressure or flushing shortly after injection
Reported at larger doses, attributed to vasoactive effects.
No effect at all
Non-response reports are common, particularly for chronic degenerative problems, and are under-represented because negative results are under-posted.
03 Dosing ranges
Figures below are documented, not recommended. Study ranges come from published protocols in the stated model; grey-market ranges are what the research community reports using and carry no safety validation of any kind.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Human trial dosing is topical or intravenous full-length Tβ4 [4]
Registered human trials used topical ophthalmic formulations or intravenous full-length Tβ4 in cardiac and neurological programmes. Neither route nor molecule matches grey-market subcutaneous TB-500, so no study-derived subcutaneous dose exists.
Animal dosing in repair models [2][3]
Pre-clinical work typically uses milligram-per-kilogram intraperitoneal or intravenous dosing of full-length Tβ4. Community subcutaneous figures are not derived from these by any validated scaling method.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Loading then maintenance
The universal community structure — higher twice-weekly dosing for four to six weeks, then a reduced maintenance frequency. The rationale is achieving tissue saturation before stepping down; there is no pharmacokinetic study supporting either the loading amount or the timing.
Twice-weekly rather than daily
Justified on the longer half-life relative to BPC-157. The actual human half-life of the fragment has not been published.
Systemic administration is sufficient
Because the mechanism is cell migration rather than local signalling, site-specific injection should be unnecessary. This is one of the better-reasoned inferences in the community canon.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
2–2.5 mg twice weekly (loading)
The standard acute-injury loading figure in circulation, typically for four to six weeks, giving 4–5 mg per week.
2–2.5 mg once weekly or every two weeks (maintenance)
The step-down phase after loading.
1–1.5 mg twice weekly (conservative)
Lower-dose approach reported for non-acute use and for blend contexts.
Blend-embedded dosing
Within KLOW, GLOW or Wolverine blends the TB-500 share is set by blend ratio rather than chosen independently — see the blend pages for the arithmetic.
| Phase | Dose per administration | Frequency | Reported duration |
|---|---|---|---|
| Loading (acute injury) | 2 – 2.5 mg | Twice weekly | 4–6 weeks |
| Loading (conservative) | 1 – 1.5 mg | Twice weekly | 4–6 weeks |
| Maintenance | 2 – 2.5 mg | Once weekly → biweekly | 4–8 weeks |
| Blend (Wolverine 1 mg) | Per blend ratio | Daily | Per cycle |
04 Synergy & interactions
Combination effects. Almost no peptide combination has been studied as a combination in humans; stack logic is overwhelmingly mechanistic inference and community practice. Each linked compound has its own page.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
No human combination data exists
There are no combination trials involving TB-500 or thymosin β4 with any other research peptide.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
TB-500 + BPC-157
The canonical pairing. The mechanistic argument is division of labour: BPC-157 establishes local vasculature and signals resident fibroblasts, TB-500 supplies the systemic migratory capacity to populate it. Two different routes to the same repair endpoint, never tested together.
TB-500 + GHK-Cu
Cell mobilisation plus matrix remodelling. GHK-Cu supplies the collagen and elastin signalling that structures whatever TB-500 mobilises.
TB-500 + KPV
Suppressing NF-κB-driven inflammation before driving migration is the stated logic for including KPV in KLOW.
TB-500 with GH secretagogues
Growth-hormone-driven collagen synthesis alongside migration and anti-fibrotic signalling. Plausible and unstudied.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
The Wolverine stack
BPC-157 + TB-500 is the most widely used peptide combination in the research community.
Component of KLOW and GLOW
TB-500 appears in both major repair blends.
Named as a non-cycled component
The Gold Standard protocol names BPC-157 and TB-500 as the two components that never need cycling.
05 Protocols
Whole schedules — dosing, titration, cycle length, and off-time — as documented in trials, as proposed from mechanism, and as circulated in the research community. Reproduced for study and comparison only.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
RGN-259 / RGN-352 clinical programmes [4]
Registered human protocols for full-length thymosin β4 in ophthalmic (topical) and cardiac/neurological (intravenous) indications. The only human protocol context in this space.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Load through the proliferative phase, maintain through remodelling
Aligning the loading phase with the biological window in which cell migration matters most. Standard wound-healing reasoning applied to an unstudied compound.
Pair with progressive mechanical loading
Tissue remodels along lines of applied stress. A migration-promoting peptide with no mechanical stimulus has no information about how to organise the tissue it builds.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
KLOW → Wolverine rotation
Four vials of KLOW, then two vials of Wolverine at 1 mg, then back — TB-500 present throughout as a non-cycled component.
4–6 week loading then maintenance
2–2.5 mg twice weekly, then weekly. The standard circulating injury schedule.
05b Condition-specific interest
TB-500 has an unusual position in this library: the molecule it is derived from, thymosin beta-4, reached genuine human clinical trials in two indications that have nothing to do with why anyone buys TB-500. Both are below, because the gap between them is the most useful thing on this page.
No approval, no trial
TB-500 is not thymosin beta-4. It is a synthetic fragment corresponding to the actin-binding region of the full 43-residue protein. Trial evidence generated with full-length thymosin beta-4 does not transfer automatically to a fragment, and no controlled human trial has been run on TB-500 itself for any indication.
TB-500 received a favourable PCAC vote for the 503A Bulks List in July 2026. A favourable vote is not an approval — see the regulatory status section below.
Theorized — the dominant use, animal evidence only
Tendon, ligament and soft-tissue injury
Pathophysiology
Repair of poorly vascularised connective tissue is limited by cell migration into the injury and by the blood supply available to sustain it. Both are slow in tendon.
Mechanistic rationale
Thymosin beta-4 is the major actin-sequestering protein in most cells, and the actin-binding fragment is proposed to promote cell migration and angiogenesis — precisely the two limiting steps. Animal models of soft-tissue injury support the mechanism. It is a coherent story and it stops at the species boundary.
Community reports
Nearly always used alongside BPC-157 as a Wolverine stack, which makes attribution to either component impossible in community reporting. Weekly loading followed by maintenance is the usual pattern, on pharmacokinetic reasoning rather than on any dose-finding study.
Components carrying the argument: Actin sequestration, cell migration, angiogenesis
Theorized — with a human-trial cousin
Wound healing and scar formation
Pathophysiology
Wound closure requires keratinocyte and endothelial migration into the defect. Chronic wounds fail at exactly that step, and excessive fibrosis in the same process produces hypertrophic scar.
Mechanistic rationale
Full-length thymosin beta-4 has been studied in dermal wound healing including pressure ulcers and epidermolysis bullosa, and reported reduced scarring in animal work alongside accelerated closure. The anti-fibrotic direction is the interesting part — most repair signals push toward more matrix, not better-organised matrix.
Community reports
Post-surgical and post-injury use is widely described, generally focused on scar appearance. Scar maturation continues for a year or more on its own, which makes any short-horizon self-assessment unreliable.
Components carrying the argument: Cell migration, anti-fibrotic signalling, angiogenesis
Study — for the parent molecule, not this fragment
Cardiac injury and ischaemia
Pathophysiology
After myocardial infarction, cardiomyocytes are lost and replaced by scar. Anything that recruits epicardial progenitor cells or limits adverse remodelling is attacking the part of the problem that reperfusion does not solve.
Mechanistic rationale
Thymosin beta-4 produced striking results in animal models of myocardial infarction — epicardial progenitor activation, improved cardiac function — and progressed to human clinical development for acute myocardial infarction. This is real clinical-stage history and it belongs to the full-length protein. Nobody has shown that an actin-binding fragment reproduces it, and nobody is monitoring cardiac function in anyone using TB-500.
Community reports
Essentially absent from community use, which is appropriate. It appears here because vendors sometimes cite the cardiac literature as evidence for a compound that literature is not about.
Components carrying the argument: Progenitor cell activation — attributed to full-length Tβ4
Study — again, the parent molecule
Dry eye and corneal injury
Pathophysiology
The corneal epithelium is avascular, heals by cell migration, and is the tissue where a migration-promoting agent should perform best.
Mechanistic rationale
A thymosin beta-4 ophthalmic formulation reached late-stage clinical trials for dry eye disease and neurotrophic keratopathy, with mixed but genuinely reported results across studies. The mechanism fits the tissue better than almost any other application of this molecule.
Community reports
No community use of TB-500 by this route, and nobody should be inventing one — an ophthalmic preparation is a sterility problem of a different order.
Components carrying the argument: Epithelial cell migration
Theorized — weakest entry here
Osteoarthritis and joint disease
Pathophysiology
Cartilage is avascular and aneural, so an angiogenic, migration-promoting agent has less obvious purchase than it does in tendon or skin.
Mechanistic rationale
The repair rationale is carried over from soft tissue rather than derived from joint-specific work. Intra-articular use is discussed in community spaces; the risk of a septic joint from non-clinical injection is the dominant consideration and it is procedural rather than pharmacological.
Community reports
Usually as part of a KLOW or Wolverine protocol, so no attribution is possible.
Components carrying the argument: Extrapolated from soft-tissue repair
Theorized — the premise is contested
Myofascial pain — the premise problem
Pathophysiology
Fibromyalgia is a disorder of central pain processing. It is not characterised by demonstrable structural damage to muscle or fascia, which is precisely what distinguishes it from a soft-tissue injury.
Mechanistic rationale
The rationale offered for TB-500 in fibromyalgia is tissue repair. Repair of what? If there is no structural lesion, a repair agent has nothing to act on. This is the clearest case in the library of a mechanism being applied to a condition whose defining feature is the absence of the thing that mechanism addresses.
Community reports
Reports exist and are positive, as they are for nearly everything in fibromyalgia — a condition with a large placebo response and a fluctuating natural history.
Components carrying the argument: Actin sequestration, cell migration — wrong target
Theorized — narrower and more defensible
Where the rationale might hold — comorbidity
Pathophysiology
People with fibromyalgia frequently also have genuine musculoskeletal injuries, and central sensitisation amplifies the pain from them.
Mechanistic rationale
A soft-tissue repair agent has a target in the comorbid injury, not in the fibromyalgia. That is a narrower and considerably more defensible claim than treating the syndrome, and it is worth stating clearly because it is the version that survives scrutiny.
Community reports
Users who describe benefit often describe it in a specific region rather than in the diffuse pain that defines the condition — consistent with this reading.
Components carrying the argument: Repair of a real lesion, if one exists
| Condition | Whose evidence? | Tier | The thing to know |
|---|---|---|---|
| Tendon / ligament | TB-500 rationale | Animal | The dominant use; no human trial |
| Wound healing / scar | Full-length Tβ4 | Human, early | Anti-fibrotic direction is the interesting part |
| Cardiac injury | Full-length Tβ4 | Clinical stage | Cited as evidence for a fragment it is not about |
| Dry eye / cornea | Full-length Tβ4 | Late-stage trials | Best tissue match; not a community route |
| Osteoarthritis | Extrapolated | None | Intra-articular injection risks a septic joint |
| Fibromyalgia | Extrapolated | None | No structural lesion for a repair agent to act on |
What actually has evidence for these conditions
For tendinopathy: progressive mechanical loading — heavy slow resistance or eccentric protocols over months — has the best evidence of any intervention and beats every injectable it has been compared against. Load management and time do most of the rest.
For chronic wounds: debridement, offloading, moisture balance, infection control, and glycaemic control where diabetes is present. For scar: silicone, pressure, sun protection and patience — scars remodel for a year or more.
For cardiac disease: reperfusion within its window, then the four pillars of heart failure therapy, each with independent mortality data. Cardiac rehabilitation is under-referred and improves survival.
For fibromyalgia: pregabalin, duloxetine and milnacipran are approved, and graded exercise combined with cognitive behavioural therapy has the strongest evidence of any intervention. The treatments that work act centrally, on pain processing — which is the yardstick a tissue-repair rationale should be held against.
06 Handling, reconstitution & storage
Physical-chemistry reference for laboratory handling of the lyophilised material. Reproduced so that stability and concentration mathematics can be studied — see the calculator for the arithmetic and the reconstitution guide for sterile technique.
Reconstitution
Supplied lyophilised, most commonly 2, 5 or 10 mg per vial. Reconstituted with bacteriostatic water. Because doses are in whole milligrams rather than micrograms, dilution volumes are usually chosen to make a full or half-syringe convenient.
Storage
Lyophilised: −20 °C for long-term, refrigerated for shorter periods. Reconstituted: 2–8 °C.
Common vial sizes
Most commonly 2 mg, 5 mg and 10 mg lyophilised vials.
Stability notes
Note the product-identity problem: vials labelled TB-500 vary between suppliers in whether they contain the short fragment or full-length thymosin β4. Certificates of analysis, where supplied, should state which.
07 Legal & regulatory status
Regulatory status changes and differs by country. This is a summary for orientation, not legal advice — check your own jurisdiction.
Not approved for human use. Sold as a research chemical. Full-length thymosin β4 has been the subject of registered clinical trials but has no marketing approval for systemic use.
TB-500 is not a standardised chemical entity in the grey market — the label covers both the short actin-binding fragment and full-length Tβ4 depending on supplier.
Regulatory update — current as at August 2026
On 23–24 July 2026 the FDA's Pharmacy Compounding Advisory Committee voted to recommend TB-500 for inclusion on the Section 503A Bulks List (8–6, one abstention). It was one of six peptides recommended — alongside BPC-157, KPV, TB-500, MOTS-c, Semax and Epitalon — out of seven considered.
This followed the FDA's announcement of 15 April 2026 removing twelve peptides from Category 2, the designation for substances judged to raise significant safety concerns. That removal stripped away the basis for enforcement against compounders but did not itself authorise anything, leaving these compounds in a regulatory grey area pending the PCAC review.
A PCAC recommendation is not an approval, and the 503A Bulks List is not a drug approval either. It is also worth knowing that July 2026 was the second round: across two sittings in October and December 2024 the same committee reviewed seven substances — among them ipamorelin, kisspeptin-10, AOD-9604, CJC-1295 and thymosin alpha-1 — and rejected all seven. Two separate things are being conflated in almost every write-up of the 2026 decision:
- The vote is advisory. PCAC recommendations are non-binding. The pathway from here runs: removal from Category 2 (done, April 2026) → PCAC recommendation (done, July 2026) → placement in Category 1 through notice-and-comment rulemaking, which commonly takes eight to twelve months → and the HHS Secretary must sign off on any addition to the list. Nothing is lawfully compoundable on the strength of the vote alone.
- Even a successful listing would not make these approved drugs. Inclusion on the 503A Bulks List permits a licensed compounding pharmacy to use the substance in a compounded preparation for an individual patient with a prescription. It says nothing about the compound being demonstrated safe and effective — no efficacy trial is required, and none of these has one.
- It would not legitimise research-chemical supply. A compounding pathway runs through a licensed pharmacy and a prescriber. Grey-market vials labelled "research use only" are not that, and nothing in this decision changes their status.
Regulatory and trial claims re-checked against primary sources on 18 August 2026. Checked: PCAC vote 23-24 July 2026 and the 503A pathway; the rat chronic-ischaemia long-term vs short-term dosing comparison, the negative pig ischaemia-reperfusion study, and phase 1 repeated-dose tolerability. Approvals, trial readouts and compounding decisions move faster than anything else on this page — a date here means someone looked, not that nothing has changed since.
Anti-doping
TB-500 is explicitly prohibited by WADA. Thymosin β4 and its analogues fall under S2 (growth factors and related substances) and TB-500 has been named in anti-doping enforcement actions, notably in equine sport. Prohibited at all times.
§ Sources & further reading
Links resolve to PubMed records, trial registries, publisher pages or primary documents. Where a body of work rather than a single paper is cited, the link opens a PubMed query so the full result set — including newer papers than this page — can be reviewed. Verify every claim against the primary source before relying on it.
- Goldstein AL, Hannappel E, Kleinman HK. Thymosin β4: actin-sequestering protein moonlights to repair injured tissues. Trends Mol Med.Review or meta-analysis
- PubMed: thymosin beta 4 — wound healing, angiogenesis and tissue repair (live query)Database or literature search
- PubMed: thymosin beta 4 — cardiac repair, fibrosis and neurological recovery models (live query)Database or literature search
- ClinicalTrials.gov: registered thymosin beta 4 trials (RGN-259, RGN-352)Registered clinical trial
- PubMed: thymosin beta 4 expression, tumour progression and metastasis (live query)Database or literature search
- Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury — long-term vs short-term dosing schedules.Pre-clinical / animal study
- Systemic Dosing of Thymosin Beta 4 before and after Ischemia Does Not Attenuate Global Myocardial Ischemia-Reperfusion Injury in Pigs. 2016.Pre-clinical / animal study
- WADA Prohibited List (current edition) — S2 growth factorsRegulatory / official document
Reminder
For educational and research reference only. Nothing on this site is medical advice, a recommendation, or an instruction to administer any substance to a human being. Every figure on this page is a record of what has been reported, not a recommendation. Full disclaimer.