TB-500
Research PeptideAlso known as: Thymosin Beta-4 · Thymosin β4 · Tβ4 · TB4 · Timbetasin · Thymosin Beta-4 Fragment (17-23) · Ac-LKKTETQ · TB4-Frag · RGN-137 · RGN-259
Preliminary Human
"TB-500" refers to either a 7-amino-acid heptapeptide (Ac-LKKTETQ) or full-length 43-residue thymosin beta-4 depending on the product — research peptide vendors typically sell the latter under the former name. Human evidence is preliminary at best: topical wound-healing Phase 2 RCTs (RGN-137), ophthalmic Phase 3 SEER-1 (n=18) which missed its primary endpoint, and IV safety studies in healthy volunteers — all of which are RegeneRx-sponsored except the 2021 Chinese Phase 1 recombinant-hTβ4 study. The musculoskeletal repair claim dominating the research peptide market has zero human RCT evidence.
Two different compounds are sold as 'TB-500'
"TB-500" historically referred to a 7-amino acid heptapeptide (Ac-LKKTETQ, MW ~809 Da) — the compound sold as a veterinary product for horses and greyhounds in the early 2010s. The research peptide market now overwhelmingly sells full-length thymosin beta-4 (43 amino acids, MW ~4,964 Da) under the same "TB-500" label, even though the two are structurally distinct molecules with different pharmacokinetics and activity spectra. Virtually all human clinical trial data is for the full-length protein. Without ESI-MS confirmation on a product COA, you cannot tell which compound is in the vial.
Research use only. Not approved for human consumption in any jurisdiction listed here unless the Regulatory Status table below explicitly states otherwise.
Evidence Tier
Preliminary Human
Human Studies
4
FDA Status
503A Category 2
WADA Status
Prohibited (S2)
Mol. Weight
4963.5 Da
Last Reviewed
Apr 20, 2026
Claimed benefits by evidence tier
Column header colour matches the tier
Preliminary Human4
- Accelerates wound healing in chronic ulcers (topical)
- Treats neurotrophic keratopathy (ophthalmic, RGN-259)
- Improves dry eye symptoms (ophthalmic, RGN-259)
- Cardiac protection / heart-attack recovery
Animal Only4
- Accelerates soft-tissue injury repair (tendon, ligament, muscle)
- Reduces scar formation
- Promotes hair growth
- Neuroprotection / stroke recovery
Anecdotal1
- General athletic performance enhancement
Unsupported1
- Anti-aging / longevity
Regulatory watch
FDA Pharmacy Compounding Advisory Committee meeting — TB-500 / Thymosin Beta-4 on the agenda for wound-healing indication review. Meeting July 23–24, 2026 at FDA White Oak Campus, Silver Spring, MD. Public docket FDA-2025-N-6895 open through July 22, 2026.
Most consequential near-term regulatory event for TB-500 in the US. PCAC could recommend: (a) adding Tβ4 to the 503A Bulk Drug Substances List — giving compounding pharmacies a legal pathway for prescription-based preparation; (b) maintaining Category 2 restriction; or (c) further study. Reclassification to 503A permission is NOT the same as FDA drug approval, but would meaningfully change the US legal landscape for compounded Tβ4.
Expected 2026-07-24 · Docket FDA-2025-N-6895 · FDA-2025-N-6895
Phase 3 SEER-2 and SEER-3 ophthalmic trials enrolling (RGN-259, RegeneRx)
SEER-2 and SEER-3 are designed to replicate the underpowered SEER-1 primary-endpoint result. If either succeeds, this would be the first pathway to FDA approval for any Tβ4 formulation — but for ophthalmic (topical-to-eye) use only, not systemic injectable research-market use.
· Source
Vendors selling TB-500
Found 12 vendors currently offering TB-500 in their catalog.
🇪🇺Particle Peptides
Slovakia
COA Coverage
25/25
100%
✓ HPLC✓ MS✓ Endo✓ Ster✓ Metals
Verified Peptides
COA Coverage
138/138
100%
✓ HPLC✓ MS✓ Endo✓ Ster— Metals
🇺🇸Soma Chems
USA
COA Coverage
60/64
94%
✓ HPLC✓ MS✓ Endo— Ster— Metals
🇺🇸Sports Technology Labs
USA
COA Coverage
57/61
93%
✓ HPLC✓ MS— Endo— Ster— Metals
Vida Labz
COA Coverage
48/49
98%
✓ HPLC— MS— Endo— Ster— Metals
Panda Peptides
COA Coverage
33/37
89%
✓ HPLC— MS— Endo— Ster— Metals
Amino Amigos
COA Coverage
10/39
26%
✓ HPLC✓ MS— Endo— Ster— Metals
🇺🇸BioLongevityLabs
USA
COA Coverage
43/89
48%
✓ HPLC✓ MS✓ Endo✓ Ster— Metals
SwissChems
COA Coverage
23/52
44%
✓ HPLC✓ MS— Endo— Ster— Metals
🇺🇸Core Peptides
USA
COA Coverage
18/103
17%
✓ HPLC✓ MS— Endo— Ster— Metals
Pure Tested Peptides
COA Coverage
3/27
11%
✓ HPLC— MS✓ Endo— Ster— Metals
Blue Sky Peptide
No verified COAs
COA Coverage
0/45
0%
— HPLC— MS— Endo— Ster— Metals
All TB-500 products
Every TB-500 product across 12 verified vendors — sorted by vendor trust tier, then by COA purity (quantified reports beat unquantified), then by most recent COA date.
About this peptide
Plain English
The human body produces a protein called thymosin beta-4 in almost every cell, and when tissues are injured, this protein helps orchestrate the repair process — it encourages cells to migrate into the damaged area, promotes the growth of new blood vessels, and damps down inflammation. "TB-500" is the name given to either a fragment of that protein (a 7-amino-acid piece) or the full protein itself, depending on which product you are looking at. Research into thymosin beta-4 spans decades and multiple clinical trials, mostly focused on wound healing and eye conditions. None of this research has yet resulted in an approved drug for human use anywhere in the world, and the compound sold in research peptide markets is not regulated as a medicine.
Technical
Thymosin beta-4 (Tβ4) is a 43-residue, N-terminally acetylated polypeptide constitutively expressed at high concentrations in the cytosol of most mammalian cell types. Its primary structural feature — the conserved LKKTET motif at residues 17–22 — confers high-affinity binding to monomeric G-actin (Kd ~0.5–0.7 μM), making Tβ4 the principal G-actin sequestering protein in many tissues. Beyond actin regulation, Tβ4 modulates NF-κB, VEGF, and ILK/AKT signaling, producing pleiotropic effects on cell migration, angiogenesis, stem-cell mobilization, and inflammation suppression. The synthetic heptapeptide TB-500 (Ac-LKKTETQ, residues 17–23) retains the core actin-binding domain and has been shown to independently promote angiogenesis and cell migration in vitro and in animal models, though its activity spectrum differs from full-length Tβ4. Clinical development of full-length Tβ4 (under INN timbetasin) has been conducted primarily by RegeneRx Biopharmaceuticals across wound-healing (RGN-137 topical gel), ophthalmic (RGN-259 eye drops), and cardiovascular indications through Phase 2 and limited Phase 3 trials; no formulation has achieved regulatory approval in any jurisdiction.
Mechanism of action
G-actin sequestration / cytoskeletal regulation
Tβ4 binds monomeric G-actin with high affinity via the LKKTET motif, sequestering it from polymerization into F-actin. The resulting shift in G-actin/F-actin ratio affects lamellipodium formation, cell polarity, and directional migration. The LKKTETQ sequence must adopt a non-helical conformation to bind actin.
Angiogenesis via VEGF upregulation
Tβ4 upregulates VEGF expression in endothelial cells and promotes endothelial differentiation, migration, and tube formation. In animal models, Tβ4 administration increases blood-vessel density at wound sites. The angiogenic effect is preserved in the heptapeptide fragment (LKKTETQ), indicating the actin-binding domain itself drives this activity.
Anti-inflammatory / NF-κB suppression
Tβ4 downregulates NF-κB signaling and reduces pro-inflammatory cytokine production (TNF-α, IL-1β, IL-6) in macrophages and other immune cells. In animal wound models, Tβ4 application reduces inflammatory infiltrate and shifts the microenvironment toward repair.
Cardiac progenitor cell mobilization / ILK-AKT survival signaling
In rodent myocardial infarction models, Tβ4 activates quiescent epicardial progenitor cells, induces their migration into the myocardium, and promotes differentiation into cardiomyocytes and smooth muscle. Tβ4 also activates ILK and AKT survival signaling, reducing post-ischemic cardiomyocyte apoptosis. The human correlate is observational only (REGENERATIVE-IHD).
The majority of mechanistic evidence derives from cell-culture systems and rodent models. Rodent wound-healing, angiogenesis, and cardiac-repair models do not reliably predict human outcomes. Phase 1 human IV studies confirm the compound is bioavailable and tolerated intravenously but do not validate these specific mechanistic pathways in humans. Extrapolating from rodent cardiac repair (which involves epicardial activation not well-characterized in adult humans) to claims of cardiac regeneration in people is speculative. Additionally, all human clinical data uses full-length Tβ4; whether the heptapeptide TB-500 activates the same pathways in humans is unconfirmed.
Key studies
A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers (2010)
Ruff D, Crockford D, Girardi G, Zhang Y · Annals of the New York Academy of Sciences
- Participants
- Healthy adult volunteers (n not specified in abstracts; multiple ascending-dose cohorts)
- Methodology
- Randomized, double-blind, placebo-controlled Phase 1a/1b. Single IV doses: 42, 140, 420, 1260 mg. Multiple doses: same range, once daily for 14 days.
- Result
- No dose-limiting toxicities or serious adverse events. Most common AEs (headache, upper respiratory infection) at rates similar to placebo. Dose-proportional pharmacokinetics with increasing half-life at higher doses.
Honest read
This is the most important safety study for IV administration of full-length Tβ4 in humans. Limitations: sample size per cohort not reported in accessible summary; short follow-up; no immunogenicity assessment reported; dosed from 42 mg (very high compared to common research peptide usage). This study does not address subcutaneous administration pharmacokinetics or sub-therapeutic dosing safety.
Thymosin beta-4 and venous ulcers: clinical remarks on a European prospective, randomized study on safety, tolerability, and enhancement on healing (2007)
Guarnera G, DeRosa A, Camerini R (Italian Wound Healing Association) · Journal of Wound Care
- Participants
- 72 patients with chronic venous stasis or pressure ulcers across 8 sites in Italy and Poland
- Methodology
- Randomized, double-blind, placebo-controlled. Three escalating concentrations of topical RGN-137 gel (0.01%, 0.03%, 0.1%) vs placebo, once daily up to 84 days, on background standard of care.
- Result
- All doses safe and well-tolerated. No drug-related SAEs. Mid-dose (0.03%) appeared most active, showing accelerated wound healing onset vs placebo. Approximately 25% of patients achieved complete healing within 3 months (small-to-moderate wound subgroup).
Honest read
This is the strongest human wound-healing evidence for Tβ4. However: (1) n=72 is underpowered for definitive efficacy claims; (2) no independent replication by separate research groups; (3) sponsor (RegeneRx) has a commercial conflict of interest; (4) topical gel formulation — cannot be extrapolated to injectable TB-500 sold in research markets; (5) full peer-reviewed publication came later (Goldstein 2012, PMID 23050815); the 2007 reference is a clinical proceedings paper.
0.1% RGN-259 (Thymosin ß4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial (2023)
Sosne G et al. · International Journal of Molecular Sciences 24(1):554
- Participants
- 18 adults with neurotrophic keratopathy (Stage 2 or 3)
- Methodology
- Randomized, double-blind, placebo-controlled Phase 3. RGN-259 (0.1% ophthalmic solution) vs placebo eye drops for 4 weeks.
- Result
- 6/10 RGN-259 patients vs 1/8 placebo patients achieved complete corneal healing at 4 weeks. Primary endpoint (p=0.0656) MISSED statistical significance. Secondary endpoint at day 43 met (p=0.0359). Ocular comfort significantly improved vs placebo.
Honest read
The most rigorous human trial of Tβ4. Key limitations: n=18 is very small — the trial was almost certainly underpowered for the primary endpoint; the p=0.0656 miss is clinically meaningful but statistically not significant by conventional thresholds; single-center/sponsor (RegeneRx) with conflict of interest; ophthalmic route — cannot be extrapolated to systemic injectable use; SEER-2 and SEER-3 currently enrolling to confirm.
A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers (2021)
Wang et al. · Journal of Cellular and Molecular Medicine
- Participants
- 54 healthy subjects (single-dose cohorts); 30 healthy subjects (multiple-dose cohorts)
- Methodology
- Randomized, double-blind, placebo-controlled Phase 1. Single IV doses: 0.05, 0.25, 0.5, 2.0, 5.0, 12.5, 25.0 μg/kg (7 cohorts). Multiple dose: 0.5, 2.0, 5.0 μg/kg daily × 10 days (3 cohorts).
- Result
- All doses safe and well-tolerated. No dose-limiting toxicities or SAEs. Adverse events mild to moderate. Dose-proportional PK; no obvious accumulation after multiple doses.
Honest read
Used recombinant (bacterially-expressed) Tβ4 which differs from synthetic Tβ4 in potential glycosylation and folding. The dose range (μg/kg) is far lower than the Ruff 2010 study (mg range IV), making direct comparison difficult. China-only healthy-volunteer study; ethnic and population diversity considerations apply. Independently important because it confirms IV safety in a second population by a non-RegeneRx group.
The actin binding site on thymosin beta4 promotes angiogenesis (2003)
Dominguez JN, de la Rosa A, Navarro F et al. · FASEB Journal
- Participants
- In vitro endothelial cells; mouse matrigel angiogenesis model
- Methodology
- Cell-culture migration assay; Matrigel tube-formation assay; mouse dorsal-sac angiogenesis model. Used full-length Tβ4 and truncated peptide fragments.
- Result
- The heptapeptide Ac-LKKTETQ (TB-500) independently promotes angiogenesis and endothelial cell migration; deletion mutants that cannot bind actin lose angiogenic activity. Establishes that TB-500 (the heptapeptide) has independent biological activity.
Honest read
Key mechanistic study confirming the heptapeptide has real biological activity, not just the full-length protein. However, all data is in vitro/animal — does not establish clinical efficacy of the heptapeptide in humans.
Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography–mass spectrometry (2012)
Teale P et al. · Journal of Chromatography A
- Participants
- Equine (horses, in vivo dosing study)
- Methodology
- Horses given TB-500 (heptapeptide); urine and plasma sampled; LC-MS/MS method developed for detection.
- Result
- Validated LC-MS/MS method capable of detecting TB-500 (Ac-LKKTETQ) in equine urine and plasma. Detection window established.
Honest read
This study confirms (a) TB-500 the heptapeptide was a commercially available product administered to horses, (b) the compound is detectable by mass spec, and (c) doping in equine sport was sufficiently widespread to merit a dedicated analytical method paper. This is not efficacy evidence.
Role of thymosin beta4 in tumor metastasis and angiogenesis (2003)
Goldstein AL, Hannappel E, Sosne G, Bhatt DL et al. (editorial review context; original paper Sharp et al.) · Journal of the National Cancer Institute 95(22):1674
- Participants
- B16-F10 melanoma mouse xenograft model
- Methodology
- B16-F10 melanoma cells transfected to overexpress Tβ4; tumor growth and metastatic lung nodules compared to controls.
- Result
- Tβ4 overexpression significantly increased tumor size, number of metastatic lung nodules, and blood-vessel density in solid tumors (4.4-fold increase in vessels). VEGF upregulation identified as key mediator.
Honest read
This is the primary animal-model evidence for the cancer-growth concern associated with Tβ4's pro-angiogenic mechanism. Important limitations: overexpression model (forced supraphysiological levels) ≠ exogenous peptide administration; mouse xenograft ≠ human oncology; this specific risk has not been studied in human TB-500 users or clinical trials. The finding does not mean administered TB-500 causes cancer — it means the biological mechanism has a plausible oncological risk that has not been adequately evaluated.
Research timeline
- 1965
Thymosin fraction isolated from bovine thymus by Goldstein, White et al. at Albert Einstein College of Medicine. Heterogeneous initial fractions.
- 1981
Thymosin beta-4 identified and sequenced as a distinct 43-amino acid peptide (Low et al.).
- 1991
Safer & Bhatt (Science) identify Tβ4 as the principal G-actin sequestering protein in mammalian cells.
- 1999
Malinda et al. demonstrate Tβ4 accelerates wound healing in corneal and dermal animal models.
- 2003
First documented cancer-concern signal: Goldstein group editorial on Tβ4 overexpression driving tumor growth and metastasis in B16-F10 mouse xenografts (JNCI).
- 2003
Dominguez et al. (FASEB J) show the heptapeptide Ac-LKKTETQ independently promotes angiogenesis — basis for marketing the fragment as biologically active.
- 2004
Crystal structure of the Tβ4–G-actin complex solved (Irobi et al.).
- 2007
European Phase 2 RCT of topical RGN-137 gel in venous-stasis and pressure ulcers published (n=72). First meaningful human trial data for Tβ4.
- 2009
RegeneRx reports Phase 2 results for NCT00832091 (72 patients, venous-stasis ulcers). Mid-dose most active; safe and well-tolerated.
- 2010
Ruff et al. Phase 1 IV safety in healthy volunteers — single doses 42–1260 mg plus 14-day multiple dose. No SAEs.
- 2010
Smart/Riley/Bhatt groups publish cardiac-epicardial-progenitor rodent studies — beginning of the cardiovascular research pipeline.
- 2011
WADA adds thymosin beta-4 and derivatives (including TB-500) to the Prohibited List under S2. Basis: equine doping market and plausible performance-enhancing mechanism.
- 2012
Teale et al. publish equine LC-MS doping-control method for TB-500 (Ac-LKKTETQ). Confirms the compound was widely administered to racehorses and greyhounds.
- 2012
Full peer-reviewed publication of the RGN-137 Phase 2 dermal healing data (Goldstein & Bhatt).
- 2015
REGENERATIVE-IHD UK stem-cell trial reports correlative finding — endogenous Tβ4 elevated in stem-cell responders. Observational only; exogenous Tβ4 not administered.
- 2021
Wang et al. first-in-human Phase 1 of recombinant human Tβ4 in healthy Chinese volunteers (0.05–25 μg/kg IV). Independent (non-RegeneRx) confirmation of IV safety.
- 2023
SEER-1 Phase 3 results published (RGN-259, ophthalmic, n=18). Primary endpoint missed (p=0.0656); secondary endpoint met (p=0.0359). SEER-2 and SEER-3 enrolling.
- 2024
FDA places thymosin beta-4 / TB-500 on Category 2 of the 503A bulk drug substances interim list, citing immunogenicity and insufficient human safety data.
- 2026
April 16, 2026: FDA Federal Register notice of PCAC meeting — TB-500 / Thymosin Beta-4 among 7 peptides scheduled for review. Docket FDA-2025-N-6895. July 23–24 2026 meeting will decide on potential reclassification.
What we don't know
- Pharmacokinetics of the heptapeptide TB-500 (Ac-LKKTETQ) in humans — all published PK is for full-length Tβ4. The two molecules have MW ~809 vs ~4,964 Da, different absorption, distribution, and clearance.
- Subcutaneous and intramuscular bioavailability — all Phase 1 trials used IV administration, but the research peptide market overwhelmingly uses subcutaneous injection. SC Tmax, Cmax, and duration are unestablished.
- Long-term safety in humans — the longest published human exposure is 14 days IV (Ruff 2010). No long-term human safety data at any dose or route.
- Immunogenicity — the FDA cited immunogenicity concerns in the Category 2 decision. No published human anti-Tβ4 antibody induction studies; cross-reactivity with endogenous Tβ4 is uncharacterized.
- Cancer risk in humans — the pro-angiogenic mechanism has a plausible tumor-promotion pathway confirmed in mouse overexpression models. No human epidemiological or clinical trial data on cancer incidence with exogenous Tβ4 or TB-500.
- Efficacy for musculoskeletal injuries (tendon, ligament, muscle) — the primary use case in the research peptide market. No published human RCTs for any orthopedic or sports-injury indication.
- Optimal dose, route, and schedule for any indication — even in wound healing, Phase 2 data suggests a mid-dose sweet spot with a non-monotonic dose-response curve, but definitive dosing is unresolved.
- Drug interactions — no published human studies with NSAIDs, corticosteroids, immunosuppressants, anticoagulants, or growth factors.
- Whether the heptapeptide and full-length Tβ4 are therapeutically interchangeable — most vendors sell them under the same "TB-500" label; they are structurally different compounds with different MWs and activity spectra.
- Oral bioavailability — not established. Peptides of this size are generally not orally bioavailable without specific formulation technology, but neither compound has been formally studied orally.
Regulatory status
| Jurisdiction | Status | Details | Last Verified | Source |
|---|---|---|---|---|
| United States (FDA) | 503A Category 2 | FDA 503A Bulk Drug Substances Interim List — Category 2 (presenting potential significant safety risks). Compounding under 503A currently restricted pending PCAC review. Cited FDA safety concerns: immunogenicity and insufficient human safety data. Docket FDA-2025-N-6895 is open ahead of the Pharmacy Compounding Advisory Committee meeting scheduled July 23–24, 2026 at FDA White Oak Campus; the committee will consider wound-healing indications. PCAC review is a step toward potential reclassification, not FDA drug approval. | 2026-04-20 | |
| Canada (Health Canada) | Not Authorized | Unauthorized injectable drug — not approved or authorized for human use. Health Canada has actively issued warnings against injectable peptide products including Tβ4 / TB-500. April 2025 warning targeting "Prime Research" peptide products specifically. Health Canada does not recognize "research use only" as a carve-out for injectable unapproved drugs. | 2026-04-20 | |
| United Kingdom (MHRA) | Not Authorized | Not licensed as a medicine — no UK Marketing Authorization or PLPI exists for any Tβ4 / TB-500 product. Sold under "research chemical" labeling only. Illegal to supply for human consumption without a prescription or manufacturer's license. Subject to the Medicines Act 1968 as an unlicensed medicinal product if sold for human use. | 2026-04-20 | |
| European Union (EMA) | Not Authorized | No EMA-approved product. No centralized Marketing Authorization identified for any Tβ4 / TB-500 formulation. No EMA orphan designation or CHMP scientific opinion identified. Compounding varies by member state and generally requires national medicines agency authorization; EMA does not regulate compounding centrally. | 2026-04-20 | |
| Australia (TGA) | Prescription Only | Schedule 4 (Prescription Only Medicine), Appendix D Item 5. Prescription required for legal possession; "research use only" labeling does not create a carve-out under Australian law, and possession without a valid prescription is a criminal offense. Compounding permitted under TGA exemptions only with prescription and strict clinical justification. TGA rationale: growth factor affecting muscle, tendon, ligament, and vascularisation — experimental in humans with carcinogenic and cardiovascular concerns explicitly cited. The TGA also maintains an active safety alert on unapproved peptides as a class. | 2026-04-20 | |
| WADA | Prohibited (S2) | Prohibited at all times (in- and out-of-competition) under Section S2 — Peptide Hormones, Growth Factors, Related Substances and Mimetics — as a non-specified substance (higher severity for violations). Prohibited since 2011, following documented equine doping use and plausible human performance-enhancing mechanism. The 2026 Prohibited List maintains S2 status. Both the Ac-LKKTETQ heptapeptide and full-length thymosin beta-4 are covered by this prohibition. Validated LC-MS detection methods exist for both forms; athletes subject to WADA testing should consider the compound detectable. | 2026-04-20 |
Safety profile
Reported side effects
- Headache (Ruff 2010 IV, incidence similar to placebo in several cohorts)
- Upper respiratory infection (Ruff 2010 IV)
- Mild-to-moderate adverse events (Wang 2021 IV recombinant hTβ4)
- No dose-limiting toxicities or SAEs in any published human trial
- No published safety data for subcutaneous injection of synthetic TB-500 (heptapeptide) in humans — the route most common in research peptide use
Theoretical concerns
Cancer growth promotion via VEGF-mediated angiogenesis
Tβ4 upregulates VEGF, driving new blood-vessel formation. Mouse overexpression studies (Sharp et al. / Goldstein 2003 JNCI) show forced supraphysiological Tβ4 increases tumor size and metastatic lung nodules 4.4-fold. Overexpression ≠ exogenous administration, and mouse oncology ≠ human outcomes — but the mechanism is real and the risk in humans has not been quantified. Anyone with active or suspected malignancy, or a family history of angiogenesis-dependent cancers, should treat this as a genuine concern. TGA cited carcinogenicity explicitly in its Schedule 4 rationale.
Severity: possible
Autoimmunogenicity against endogenous Tβ4
Exogenous administration of a peptide that mimics an endogenous protein carries theoretical risk of anti-drug antibodies that cross-react with endogenous Tβ4, potentially disrupting normal actin-cytoskeletal regulation and tissue maintenance. The FDA cited immunogenicity concerns in the Category 2 decision. No published human anti-drug antibody data.
Severity: theoretical
Methionine-sulfoxide impurity from oxidation of Met6
The Met residue at position 6 of full-length Tβ4 is susceptible to oxidation to Met-sulfoxide — a chemically distinct, likely biologically inactive form. Systemic injection of oxidized peptide introduces an incompletely characterized impurity. HPLC purity alone cannot distinguish Met-Tβ4 from Met(O)-Tβ4; MS confirmation is required. This is an analytical / product-quality concern, not an adverse-event signal.
Severity: possible
Interaction with anticoagulants
Tβ4 promotes angiogenesis and new blood-vessel formation. Theoretical augmentation of bleeding risk in the context of anticoagulation (warfarin, heparin, NOACs). Uncharacterized in any human study.
Severity: theoretical
Contraindications
- Active malignancy, personal history of cancer, or family history of angiogenesis-dependent cancers (mechanistic pro-angiogenic concern + TGA rationale)
- Pregnancy and lactation (no safety data; constitutes unauthorized unapproved drug in all jurisdictions)
- Competitive sport under WADA jurisdiction (prohibited at all times under S2)
Interactions
- No published human drug-interaction studies exist. Theoretical concerns: anticoagulants (bleeding risk augmentation via new vessel formation), immunosuppressants (unknown interaction as immune-modulatory peptide), and other growth factors / peptides commonly co-administered in research settings (no PK or PD data).
Dosing observed in the literature
These are doses from published human trials only — IV full-length Tβ4 and topical formulations (gel and ophthalmic solution). No subcutaneous injection doses appear in any published human study; the SC route and doses circulating in research peptide communities are not drawn from published clinical research. TB-500 / thymosin beta-4 is not approved for human use in any jurisdiction. Content is for research reference only and is not medical advice.
| Route | Range | Context | Source |
|---|---|---|---|
| intravenous | 42, 140, 420, 1260 mg single dose (full-length Tβ4) | Phase 1a IV safety, RegeneRx, healthy adult volunteers. | PMID:20536472 |
| intravenous | 42–1260 mg once daily × 14 days (full-length Tβ4) | Phase 1b multiple-dose IV safety, healthy adults. | PMID:20536472 |
| intravenous | 0.05–25 μg/kg single dose (recombinant hTβ4) | Phase 1 safety in healthy Chinese adults (7 ascending-dose cohorts). | PMC8419156 |
| intravenous | 0.5–5.0 μg/kg once daily × 10 days (recombinant hTβ4) | Phase 1 multiple-dose, healthy Chinese adults (3 cohorts). | PMC8419156 |
| topical | 0.01%, 0.03%, 0.1% gel once daily × up to 84 days (RGN-137) | Phase 2 RCT, chronic venous stasis / pressure ulcers. | PMID:17495250 |
| topical | 0.1% ophthalmic solution (RGN-259) | Phase 3 SEER-1 RCT, neurotrophic keratopathy — topical to the eye. | Source |
Stability & handling
- Lyophilized shelf life
- Up to 24 months at −20°C; up to 36 months at −80°C (vendor consensus; no peer-reviewed TB-500 stability study identified)
- Lyophilized storage
- −20°C routine; −80°C preferred for long-term; amber or foil-wrapped vials to protect Met6 from photo-oxidation
- Reconstitution diluents
- Bacteriostatic water (0.9% benzyl alcohol) — preferred for multi-use research aliquoting, Sterile water for injection — single-use, Acetic acid 0.1–1% — improves solubility for some peptide batches
- Reconstituted (refrigerated)
- 28–42 days at 2–8°C (vendor literature; no published analytical stability validation specific to TB-500)
- Reconstituted (room temp)
- Avoid; degradation expected within hours to 1–2 days at ambient temperature
- OK to refreeze
- No
- Light sensitive
- Yes — protect from light
Moderate-to-high light-sensitivity concern: the methionine residue at position 6 (Met6) of full-length Tβ4 is susceptible to photo-oxidation to Met-sulfoxide, more UV-sensitive than most research peptides. Store in amber vials or foil-wrapped. Aggregation / insoluble particulates are a real concern at higher concentrations — reconstitute by gentle swirling rather than vortexing, and visually inspect for turbidity or particulates before use. Reconstitution-volume accuracy matters at common research-market vial sizes (5 mg, 10 mg in 1–2 mL); pipetting errors are a leading real-world potency issue.
Frequently asked questions
What's the difference between TB-500, TB4, and thymosin beta-4?
Thymosin beta-4 (TB4 or Tβ4) is a 43-amino acid protein naturally made in human cells. "TB-500" originally referred specifically to a synthetic 7-amino acid fragment (Ac-LKKTETQ) of that protein, sold as a veterinary product for horses. Today, most research peptide vendors sell the full 43-amino acid thymosin beta-4 under the "TB-500" brand name, making the labels effectively interchangeable in the market despite being structurally different compounds with different molecular weights (~809 vs ~4,964 Da). Virtually all human clinical trial data is for the full-length protein. If you are buying "TB-500," request mass-spectrometry confirmation of which compound you actually have.
Is TB-500 approved by the FDA?
No. No form of thymosin beta-4 or TB-500 is FDA-approved for any human indication. The closest it has come is a Phase 3 ophthalmic trial (RGN-259 for neurotrophic keratopathy) that missed its primary statistical endpoint; follow-up trials are ongoing. The FDA currently places the compound in Category 2 of the 503A bulk drug substances interim list, with an advisory committee review scheduled for July 23–24, 2026. A favorable PCAC recommendation would open a compounding pathway — not a drug approval.
Is TB-500 detectable in a drug test?
Yes. WADA has prohibited thymosin beta-4 and TB-500 since 2011, and validated LC-MS detection methods exist for both the heptapeptide and full-length Tβ4 in urine and plasma. Equine sports methods were published in 2012; human sports anti-doping methods are maintained by WADA-accredited labs. Athletes subject to WADA testing — which includes virtually all professional sports globally — should consider the compound detectable and prohibited.
What is the actual human evidence for muscle and tendon repair?
There is none from controlled human trials. The musculoskeletal repair claims dominating the research peptide market are based exclusively on animal and cell studies. The only human clinical trials involve wound healing (topical gel), dry eye, and neurotrophic keratopathy (ophthalmic drops), plus IV safety studies in healthy volunteers. None of those routes or indications is the same as subcutaneous injection for tendon or muscle repair. The claim that TB-500 heals tendons and muscles in humans is animal-data extrapolation marketed as established fact.
Can TB-500 promote cancer?
Mechanistically, the concern is plausible: Tβ4 promotes VEGF-mediated angiogenesis, and new blood-vessel formation can support tumor growth. Mouse overexpression studies show increased tumor size and metastatic burden. However, overexpression models ≠ exogenous peptide administration, and mouse oncology ≠ human outcomes. No human cancer-incidence data exists for TB-500 use. The risk is unquantified, not zero. Anyone with active cancer, a history of cancer, or a family history of angiogenesis-dependent cancers should treat this concern seriously until human data exists. The TGA (Australia) specifically cited carcinogenicity in its Schedule 4 rationale.
What does the "research use only" label mean legally?
In most jurisdictions, very little. In the United States, the label defers potential FDA enforcement but does not create a legal right to purchase, use, or administer the compound as a human therapeutic. In Australia, it has no legal effect — possession without a prescription is a criminal offense regardless of label. In Canada, Health Canada does not recognize it as a carve-out for injectable unapproved drugs. In the UK, if the substance is represented as suitable for human use (or the purchaser's intent is human use), MHRA regulations may apply. The label is a vendor legal strategy, not a regulatory category.
What is the "Wolverine Stack" and is there evidence for it?
The "Wolverine Stack" refers to co-administration of BPC-157 and TB-500, a practice popular in performance and recovery communities. There is no published human clinical evidence for this combination. No pharmacokinetic interaction studies exist. No safety data for the combination exists. The theoretical rationale (both have wound-healing properties via different mechanisms) is mechanistically plausible but entirely unsupported by controlled data. The combination label is a marketing construct.
Why was TB-500 originally developed for horses?
TB-500 the heptapeptide was commercially developed and marketed as a veterinary product for racehorses and greyhounds in the early 2010s, promoted as a recovery and performance aid. It entered human use from the equine market — not through clinical development. This origin matters because: (a) the original compound was the heptapeptide, not full-length Tβ4; (b) the compound had no human clinical trial data when it entered research peptide markets; (c) WADA banned it in 2011 based on equine doping prevalence, not established human performance effects. Subsequent Tβ4 interest from wound-healing researchers provided a different — and more scientifically grounded — development path for the full-length molecule.
What should I look for on a TB-500 COA?
Four things, separately: (1) ESI-MS or MALDI-TOF confirmation of the molecular ion — ~4,964 Da for full-length Tβ4 or ~809 Da for the heptapeptide. Without mass spec you cannot verify which compound is in the vial. (2) Methionine-oxidation check: the full-length Tβ4 Met6 residue oxidizes readily to Met-sulfoxide (+16 Da), and HPLC purity alone cannot distinguish Met-Tβ4 from Met(O)-Tβ4 — MS is required. (3) Peptide content (%) distinct from HPLC chromatographic purity — stated vial masses often represent salt weight, not net peptide. Counterion identity (TFA vs acetate) should be reported; acetate is preferred for injectable research use. (4) Endotoxin (LAL) testing is standard for any injectable-intended peptide but is routinely omitted from research-grade COAs. A COA reporting only "HPLC purity ≥98%" without the above has not demonstrated what is in the vial.
Last researched: Apr 20, 2026