TB-500 (Thymosin Beta-4 Fragment): An Evidence-Graded Monograph

Direct answer

TB-500 is a synthetic peptide sold as a tissue-repair compound. It is not the full thymosin beta-4 protein; it is a short fragment — the acetylated heptapeptide Ac-LKKTETQ (residues 17–23), the actin-binding motif of thymosin beta-4 (Tβ4) (Philp et al., FASEB J 2003). That distinction matters, because almost all the human trial data belongs to full Tβ4 (the eye-drop RGN-259 program), not to the TB-500 fragment (SEER-1, PMC9820614). The repair, angiogenesis, and cell-migration findings most often attached to TB-500 come overwhelmingly from animal and cell-culture studies of Tβ4 — no published randomized controlled trials test TB-500 itself in humans (Grade C–D) (Philp & Kleinman, 2004). As of June 2026, TB-500 is not an FDA-approved drug; it is scheduled for an FDA Pharmacy Compounding Advisory Committee vote on July 23–24, 2026, and it is prohibited at all times in sport by WADA, which names thymosin-β4 and its derivatives under Section S2.3 (Growth Factors and Growth Factor Modulators) (FDA PCAC calendar; WADA Prohibited List).

What TB-500 is — and how it differs from full thymosin beta-4

The first thing to get straight is what molecule we are talking about, because vendor copy and the scientific literature are not describing the same thing.

Thymosin beta-4 (Tβ4) is a naturally occurring 43-amino-acid, ~5 kDa polypeptide found in nearly every human cell and in body fluids including blood, tears, and saliva. It is the most abundant member of the beta-thymosin family and is regarded as the principal G-actin–sequestering peptide in mammalian cells (Philp et al., FASEB J 2003; Goldstein et al., review). This full protein is what has actually been put into human clinical trials, in the form of the ophthalmic candidate RGN-259 (SEER-1, PMC9820614).

TB-500, by contrast, is the name given to a much shorter synthetic fragment: the acetylated heptapeptide Ac-LKKTETQ, corresponding to amino acids 17–23 of Tβ4 — the seven-residue actin-binding motif (Philp et al., FASEB J 2003). Researchers isolated this fragment precisely because the actin-binding domain was shown to carry much of Tβ4's angiogenic activity. The reasoning is sound; the leap that follows it often is not.

Why the distinction is load-bearing:

• They are not the same molecule. TB-500 is roughly one-sixth the length of Tβ4. It can reproduce some of Tβ4's activities in assays, but it is not a generic stand-in for the parent protein, and human outcome data for the parent does not transfer to the fragment.
• The human data belongs to the parent. The eye-drop trials below used full thymosin beta-4, not TB-500.
• The active species may not even be the fragment. A 2024 metabolism study reported that the parent Ac-LKKTETQ fragment did not enhance wound healing in vitro, whereas one of its metabolites, Ac-LKKTE, did — raising the possibility that "TB-500's" repair reputation is partly a story about a breakdown product, not the marketed compound (Rahaman et al., J Chromatogr B 2024).

Throughout this monograph we label findings by the exact molecule and species tested. For how Peptevity assigns the letter grades below, see our evidence-grading methodology.

Mechanism of action (Grade D — mechanistic / in-vitro)

The proposed mechanisms are well-characterized cell biology. Almost all of them are demonstrated in cell culture or animal tissue rather than in human outcomes, so we grade the mechanism claims D (in-vitro / mechanistic) even where a downstream tissue claim earns a slightly higher grade.

• Actin sequestration. Tβ4 binds monomeric (G-)actin in a 1:1 complex with high affinity (reported dissociation constant on the order of Kd ~0.7 µM under physiological conditions), holding a reserve of actin monomers and preventing their spontaneous incorporation into filaments until the cell needs them (Carlier et al., actin-binding studies; Goldstein et al., review). This "actin buffer" role is the molecular core of the whole story — the actin-binding motif Ac-LKKTETQ is exactly the TB-500 fragment.
• Cell migration. By regulating the available actin pool, Tβ4 influences the lamellipodia and filopodia at a cell's leading edge — the structures that drive migration. In wound and repair contexts this is invoked to explain faster recruitment of cells to an injury site (Philp & Kleinman, 2004).
• Angiogenesis. In cultured human umbilical-vein endothelial cells and chick aortic-arch models, the seven-amino-acid actin-binding motif was shown to be essential for Tβ4's angiogenic activity: peptides lacking part of that motif were inactive, and the motif alone showed near-identical activity to the full protein (Philp et al., FASEB J 2003). This cell/animal result is the strongest mechanistic case for the TB-500 fragment specifically — and it is still mechanistic.
• Anti-inflammatory signaling. In cell models, Tβ4 inhibited TNF-α–induced NF-κB activation and downstream IL-8 expression (Qiu et al., PMC3101037). This is a plausible route to reduced local inflammation but is, again, in-vitro.

So the mechanistic story is coherent and biologically grounded — it is why researchers expected tissue-repair benefit. What it does not do, on its own, is demonstrate benefit in a living person, least of all from the fragment sold as TB-500.

The evidence, by claim and species

Wound healing and dermal repair — Grade C (animal-dominant)

The "healing peptide" reputation rests overwhelmingly on animal models of full Tβ4, not on human trials of TB-500.

• In rodent dermal wound models, topical or intraperitoneal Tβ4 increased re-epithelialization by roughly 42% over saline controls at 4 days and by as much as 61% at 7 days, with greater wound contraction and increased collagen deposition and angiogenesis in treated wounds (Philp & Kleinman, 2004).
• Tβ4 has been reported to promote angiogenesis, wound healing, and even hair-follicle development in normal and aged rodents (Philp & Kleinman, 2004).

These are consistent, in places robust, animal findings. They are still Grade C: they use the full protein, in animals, and they do not establish that the injected TB-500 fragment heals tendons, ligaments, or muscle in humans — the use case the marketing centers on. There are no qualifying human musculoskeletal RCTs for TB-500 in the literature we rely on.

Corneal / ophthalmic repair — Grade B–C (mixed human trials, full Tβ4, not TB-500)

The only sustained human clinical program for this molecule is ophthalmic, and it uses full thymosin beta-4 as an eye drop (RGN-259), not injectable TB-500. The results are genuinely mixed, which is the honest summary.

• In the SEER-1 Phase 3 trial in neurotrophic keratopathy, 6 of 10 patients (60%) on 0.1% RGN-259 achieved complete corneal epithelial healing versus 1 of 8 (12.5%) on placebo — a positive direction, but in a very small sample the complete-healing comparison only reached p = 0.0656 (short of conventional significance), while a separate "significant healing" endpoint did reach p = 0.0359 (SEER-1, PMC9820614).
• In the larger ARISE-3 Phase 3 dry-eye trial (planned ~700 patients), the pre-specified co-primary endpoints were not met, although the sponsor reported statistically significant improvement in a specific symptom (ocular grittiness) and in some corneal-staining measures in subgroups (Eyewire News — ARISE-3).
• A European Phase 3 neurotrophic-keratitis trial (SEER-3) also missed its primary endpoint, attributed in part to a strong placebo response (Ophthalmology Times — SEER-3).

We grade the eye program B–C: there is real, randomized, placebo-controlled human evidence (which earns above the animal floor), but the pivotal trials have repeatedly missed their primary endpoints, and none of this evidence is for TB-500, the injectable fragment people buy. Full Tβ4 eye drops are not the same product as research-grade TB-500 powder.

Cardiac repair — Grade C–D (animal models plus an early human signal)

Tβ4 has an extensive preclinical cardiac literature and one widely cited human pilot.

• In animal models of myocardial infarction, Tβ4 reduced infarct size, limited fibrosis and cardiomyocyte apoptosis, and increased vessel density, acting through an early protective (anti-apoptotic/anti-inflammatory) phase and a later vascular/progenitor-activation phase (Bock-Marquette et al., review; cardioprotection review, Frontiers 2013).
• A small human pilot in stem-cell-treated heart-attack patients found that higher circulating Tβ4 levels after intracardiac injection were associated with symptom improvement at six months — a correlation in a tiny, non-pivotal study, and one about endogenous Tβ4 rather than administered TB-500 (cardioprotection review, Frontiers 2013).

This is interesting biology and an early human signal, but it is preclinical-dominant and associational on the human side. It does not support cardiac claims for the TB-500 fragment, and we will not present it as if it did.

Musculoskeletal / athletic recovery — Grade D–E (no qualifying human data)

This is the use case TB-500 is actually sold for — faster recovery from tendon, ligament, and muscle injury — and it is the worst-supported. There are no published human RCTs of TB-500 for musculoskeletal repair; the case is mechanistic extrapolation from the angiogenesis and migration assays above, plus animal wound work, plus user anecdote. "Heals injuries fast" as applied to TB-500 in athletes is a Grade E (anecdotal/marketing) claim that borrows a Grade C–D mechanistic story. The 2024 finding that the parent fragment may be less active than its metabolite only widens the gap between the marketing and the molecule (Rahaman et al., 2024).

The "Wolverine stack" (BPC-157 + TB-500), in context

TB-500 is frequently sold and discussed alongside BPC-157 as a tissue-repair pair, marketed under the nickname "wolverine peptide" or the "wolverine stack." That nickname is marketing, not science — there is no compound called wolverine peptide, and the framing borrows a comic-book healing reputation that the human evidence does not earn. We cover the nickname's origin and the BPC-157 side of the pairing in our note on the so-called wolverine peptide, and the companion compound in the BPC-157 monograph.

What can be said plainly: the two compounds have different proposed mechanisms (BPC-157 is a gastric-derived pentadecapeptide; TB-500 is an actin-binding Tβ4 fragment), both rest on animal-dominant evidence with no human RCTs for the stack, and no controlled study has tested the combination in people. Combining two under-studied compounds does not add their evidence together; it multiplies the unknowns. For a side-by-side of where the two diverge, see our comparison of BPC-157 vs TB-500. We mention the stack because people search for it — not because the evidence supports it.

Safety

Safety and evidence grade are separate axes (see our evidence-grading methodology); a molecule can have a tolerable short-term profile in small trials and still be essentially uncharacterized for the use and route people actually choose.

• What the human eye trials show. In the RGN-259 ophthalmic trials, topical thymosin beta-4 was generally well tolerated, with the program's setbacks being efficacy (missed endpoints), not major safety signals (SEER-1, PMC9820614). That is reassuring for an eye drop of the full protein and says little about injecting the TB-500 fragment.
• The injectable fragment is largely uncharacterized in humans. There are no long-term human safety datasets for injected TB-500. The material sold online is research-grade, produced outside Good Manufacturing Practice, with no guaranteed identity, potency, or purity — so even the known biology is layered over an unknown product (DoD OPSS).
• Plausible cautions, not scare warnings. Because Tβ4's signature activities are angiogenesis and cell migration, a reasonable theoretical concern — flagged in the research literature rather than demonstrated in humans — is the effect of a pro-angiogenic agent in the presence of occult tumor tissue, since tumors also depend on new blood vessels (Goldstein et al., review). This is a hypothesis worth a clinician's attention, not a proven harm.

We do not issue a blanket "just don't." We state the specific, sourced picture: the full-protein eye drop has a manageable short-term profile in small trials; the injectable TB-500 fragment that people actually buy is uncharacterized in humans and is an unregulated research chemical.

Legal, FDA, and anti-doping status, in plain terms (as of 2026-06-09)

The standing Regulatory status block above carries the dated summary; this section explains the nuance.

• It is not an FDA-approved drug. No TB-500 product is approved to treat, cure, or prevent any condition, and full thymosin beta-4 has not been approved either. Vendor pages claiming therapeutic effects are making unapproved drug claims.
• Compounding = volatile lane. TB-500 was on the FDA's interim 503A Category 2 list; the April 2026 removal of a peptide group from that interim list followed withdrawn nominations, which is explicitly not a safety finding or an authorization to compound. TB-500 (free base / acetate) is scheduled for a Pharmacy Compounding Advisory Committee vote on July 23–24, 2026, alongside BPC-157, KPV, MOTS-c, DSIP, Epitalon, and Semax, under docket FDA-2025-N-6895. The pathway is under active review, not affirmatively open (FDA PCAC calendar; FDA — 503A bulks).
• Banned in sport. WADA prohibits thymosin-β4 and its derivatives at all times; the 2026 Prohibited List names them under Section S2.3 (Growth Factors and Growth Factor Modulators), within the growth-factor language covering tendon/ligament/muscle protein synthesis, vascularisation, and regenerative capacity. Athletes subject to testing — and military personnel under the DoD's adoption of the WADA categories — should treat TB-500 as prohibited (WADA Prohibited List; DoD OPSS).
• Research-grade = "RUO." TB-500 sold online is labeled "research use only — not for human consumption." That label is a legal category, not a wink. For the broader framing, see our notes on what "research use only" means and whether peptides are legal, and the distinction between investigational and approved status.

Because this lane shifts — and the July 2026 PCAC vote could move it — the date matters. We review this page on the same cadence as our living 2026 regulatory tracker; if the PCAC outcome changes the status, this monograph is updated and the change is logged under our corrections policy.

Honest bottom line

TB-500 is a case study in the gap between a marketed product and its evidence. The strongest mechanistic case — actin sequestration driving cell migration and angiogenesis — is real but in-vitro (Grade D). The wound-healing reputation is animal-dominant and mostly belongs to full thymosin beta-4, not the TB-500 fragment (Grade C). The only sustained human trials use the full protein as an eye drop and have repeatedly missed their primary endpoints (Grade B–C). For the musculoskeletal recovery people actually buy it for, there are no human RCTs at all (Grade D–E) — and a 2024 study even questions whether the marketed fragment, rather than a metabolite, is the active species. TB-500 is not an FDA-approved drug, its compounding status is under active FDA review with a July 23–24, 2026 PCAC vote pending, and it is banned in sport by WADA under Section S2.3. If you read one thing into this page, read the distance between "thymosin beta-4 does interesting things in cells and animals" and "the injectable fragment heals human injuries" — and treat marketing that collapses the two, including the "wolverine stack" framing, as exactly that.

For neighboring compounds where the same animal-vs-human gap appears, compare our monograph on the healing peptide BPC-157, the copper peptide GHK-Cu, and the category overview of peptides for health and longevity. For the framing that runs through all of these, see animal vs human evidence and are peptides safe.

How we graded this page

Every claim above is tied to its strongest primary source and labeled by molecule (full Tβ4 vs the TB-500 fragment) and by species, per our evidence-grading methodology and sourcing and citation policy. Peptevity carries no advertising, no affiliate links, and sells nothing — see our conflict-of-interest and funding statement.

Primary sources

• Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. The actin binding site on thymosin β4 promotes angiogenesis. FASEB J. 2003;17(14):2103–5. PubMed 14500546
• Philp D, Kleinman HK. Thymosin beta4 promotes angiogenesis, wound healing, and hair follicle development. Mech Ageing Dev. 2004;125(2):113–5. PubMed 15037013
• Sosne G, et al. 0.1% RGN-259 (Thymosin β4) Ophthalmic Solution Promotes Healing in Neurotrophic Keratopathy: a Randomized, Placebo-Controlled, Double-Masked Phase III Trial (SEER-1). PMC9820614
• Rahaman M, et al. Simultaneous quantification of TB-500 and its metabolites… and their screening by wound-healing activities in vitro. J Chromatogr B. 2024. ScienceDirect
• Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide (angiogenesis review). Angiogenesis. 2007. SpringerLink
• Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury. Front Pharmacol. 2013. Frontiers
• U.S. Food and Drug Administration. July 23–24, 2026 Meeting of the Pharmacy Compounding Advisory Committee. FDA
• U.S. Food and Drug Administration. Bulk Drug Substances Used in Compounding Under Section 503A. FDA
• World Anti-Doping Agency. The 2026 Prohibited List (Section S2.3 — Growth Factors and Growth Factor Modulators; thymosin-β4 and its derivatives). WADA

External references appear as citations only; none of the cited institutions endorse, review, or are affiliated with Peptevity.