Section 01
What it's used for
Heart Repair Claim, Unproven
Vendors call it a heart-repair aid, but no published human trial backs this. The only finished human trial checked safety in healthy volunteers. A 2021 heart-attack trial was withdrawn before enrollment; benefits seen only in animals.
▸Clinical wording
Thymosin beta-4 (RGN-352) is described in vendor and community material as supporting cardiac repair after myocardial infarction, but no published human trial data support this. The only completed human trial tested safety, tolerability, and pharmacokinetics in healthy volunteers rather than efficacy, and a planned phase 2 efficacy trial in acute STEMI patients was withdrawn in 2021 before any subject was enrolled. Reduced infarct size, improved ejection fraction, and activation of cardiac progenitor cells are findings from animal studies only, not from human clinical trials.
Skin and Eye Wound Healing
Studied in human clinical trials for healing skin wounds and eye (corneal) injuries. Researchers believe it speeds healing by helping cells move to the wound, growing new blood vessels, and building collagen, a tissue-building protein.
▸Clinical wording
Clinical trials for dermal wound healing and corneal injuries. Accelerates healing through cell migration, angiogenesis, and collagen deposition.
Eye Drops for Dry Eye, Cornea
RGN-259 eye drops eased dry-eye symptoms in a finished mid-stage trial. A late-stage dry-eye trial is done, unpublished. A corneal-injury trial stopped early for business reasons — its 18-person study beat placebo — a second trial recruits.
▸Clinical wording
RGN-259 (thymosin beta-4 eye drops) has completed phase 2 randomized clinical trials showing improved signs and symptoms of dry eye disease. A phase 3 trial in dry eye disease is listed as completed but has no posted results or matching publication, and a phase 3 trial in neurotrophic keratopathy was terminated early for business reasons rather than completed, though its small dataset (n=18) showed a higher healing rate than placebo; a second neurotrophic keratopathy phase 3 trial is still recruiting.
Muscle, Tendon, Ligament Repair
In animal and lab-cell studies, it sped up muscle repair by attracting muscle-building cells needed for regeneration. No published study on tendon or ligament repair was found, so claims of faster healing are not supported by evidence.
▸Clinical wording
Animal and cell-based studies show thymosin beta-4 accelerates muscle repair, acting as a chemoattractant for myoblasts during regeneration. No publication specific to thymosin beta-4 in tendon or ligament repair was found, so claims of accelerated tendon and ligament repair are not supported by the evidence available.
Section 02
Mechanism of Action
Thymosin β4 (Tβ4) is a 43-amino-acid, roughly 5 kDa peptide found in most eukaryotic cells. Its reported activities start from a single biochemical event — binding of monomeric actin — and branch into separate survival, angiogenic, anti-inflammatory and progenitor-cell arms, characterized mainly in cell culture and animal models.
Holding scaffolding parts in reserve
- It grabs single actin units and holds them in a pool that cannot join the scaffolding.
- A high-resolution structure shows the peptide capping both ends of one actin unit.
- Variants missing a seven-residue stretch lose vessel-sprouting and cell-migration activity, and added actin blocks the same responses.
- In rat full-thickness wounds, resurfacing of the skin rose by 42%.
▸Clinical wording
G-Actin Sequestration and Cytoskeletal Remodeling
Tβ4 binds monomeric actin and holds it in a non-polymerizable pool. A 2 Å structure of a gelsolin-domain-1/Tβ4 hybrid shows the peptide capping both ends of the actin monomer (Irobi 2004). NMR and mutagenesis of the β-thymosin/WH2 module trace sequestration to an amphipathic N-terminal helix that recognizes ATP-bound actin, while weaker C-terminal contacts decide whether the domain blocks or feeds filament assembly (Hertzog 2004). Variants lacking the seven-residue LKKTETQ site lose endothelial migration and vessel-sprouting activity, and added soluble actin blocks the same responses (Philp 2003). In rat full-thickness wounds, Tβ4 raised re-epithelialization by 42% (Malinda 1999).
Keeping heart muscle cells alive in mice
- In embryonic mouse hearts it moved muscle and vessel-lining cells and kept heart cells alive in culture.
- It formed a complex with two scaffold proteins that switches on the survival kinase Akt.
- After a tied-off coronary artery in mice, treated hearts showed more surviving cells and better function.
- These are mouse observations; the same complex has not been mapped in human tissue.
▸Clinical wording
PINCH-ILK-Akt Survival Signaling
In embryonic mouse heart Tβ4 promoted myocardial and endothelial cell migration, kept that effect in postnatal cardiomyocytes, and raised cardiomyocyte survival in culture. Biochemically it formed a functional complex with the adaptor PINCH and integrin-linked kinase (ILK), which activated the survival kinase Akt (protein kinase B). After coronary artery ligation in mice, Tβ4 treatment was followed by upregulated cardiac ILK and Akt activity, greater early myocyte survival and improved cardiac function (Bock-Marquette 2004). These are mouse observations; the complex has not been mapped the same way in human tissue.
Raising vessel-growth signals indirectly
- It does not switch on the VEGF gene directly; instead it stabilises an oxygen-sensing protein (HIF-1α).
- In human vessel cells and mice with starved limbs it raised several vessel-growth markers and capillary density.
- Blocking two of those pathways reversed both the marker changes and the extra vessels.
- In diabetic mice, an antibody against the Tie2 receptor abolished the gain in nerve microvessels.
▸Clinical wording
HIF-1α-VEGF and Angiopoietin-Tie2 Angiogenic Signaling
Tβ4 appears to raise VEGF indirectly. Promoter-luciferase and mRNA-stability assays showed no direct transcriptional effect, whereas HIF-1α protein stability increased, and the two proteins co-localized in colon cancer tissue arrays (Jo 2010). In HUVEC and in mice with critical limb ischemia, Tβ4 overexpression raised Ang2, Tie2, VEGF-A, Notch intracellular domain and phospho-p65, and Notch or NF-κB inhibitors reversed both the marker shifts and the gains in CD31-positive capillary and α-SMA-positive arteriolar density (Lv 2020). In diabetic db/db mice, a Tie2-neutralizing antibody abolished the Tβ4-driven rise in sciatic nerve microvessel density (Wang 2019).
Calming inflamed surface cells of the eye
- In human corneal cells it stopped a master inflammation switch (NF-κB) from entering the nucleus.
- The direction depends on cell type: in vessel-lining cells the same factor was reported to rise.
- The phase III eye trial stopped early: 6 of 10 healed on drops versus 1 of 8 on placebo.
- That trial had only 18 completers, missed its day-29 endpoint, and separated two weeks after dosing.
▸Clinical wording
NF-κB Suppression in Inflamed Epithelium
In transformed and primary human corneal epithelial cells, Tβ4 at 1 µg/ml given before 10 ng/ml TNF-α suppressed NF-κB activation at 30-60 minutes, lowered p65 phosphorylation at Ser276, and blocked p65 nuclear translocation, leaving it perinuclear on immunofluorescence (Sosne 2007). The direction looks cell-context dependent: in endothelium the same factor was reported to rise under Tβ4 (Lv 2020). A phase III trial in neurotrophic keratopathy, stopped early at 18 completers, recorded epithelial defect healing in 6 of 10 on 0.1% Tβ4 drops versus 1 of 8 on placebo — short of the day-29 endpoint (p = 0.0656) but separating at day 43, two weeks after dosing stopped (p = 0.0359) (Sosne 2022).
Dormant repair cells and a released fragment
- In mice it was reported essential for coronary vessel development and drove dormant heart-surface cells to grow out.
- An enzyme clips a four-unit fragment (Ac-SDKP) off the peptide.
- In mice with lung injury that fragment lowered scar collagen and blocked the rise in two fibrosis markers.
- In rat hair follicles and injured mouse muscle it moved stem cells and muscle precursor cells.
▸Clinical wording
Progenitor Mobilization and the Ac-SDKP Cleavage Arm
Tβ4 was reported essential for coronary vessel development in mice; on quiescent adult epicardial explants it drove outgrowth and differentiation into fibroblasts, smooth muscle and endothelial cells, while knockdown lowered the cleavage product Ac-SDKP (Smart 2007). That tetrapeptide is released from Tβ4 mainly by prolyl oligopeptidase (Cavasin 2004), and in bleomycin-treated mice it reduced lung collagen and blocked the rise in TGF-β and α-SMA (Conte 2016). In rat hair follicles, nanomolar Tβ4 increased bulge stem cell migration and MMP-2 secretion (Philp 2004); in injured mouse muscle, Tβ4 mRNA rose early and the peptide chemoattracted satellite-cell-derived myoblasts (Tokura 2011).
Section 03
Biological Pathways
- G-Actin Sequestration & MotilityTβ4 binds monomeric actin and caps both ends via an N-terminal helix, holding a non-polymerizable pool; peptides lacking its LKKTETQ motif lose migration activity, and Tβ4 raised rat re-epithelialization by 42%.
- PINCH-ILK-Akt Survival SignalingIn mouse heart tissue, Tβ4 forms a complex with the adaptor PINCH and integrin-linked kinase, activating Akt; after coronary ligation this brought greater early cardiomyocyte survival and better cardiac function.
- HIF-1α/VEGF & Ang2/Tie2 AngiogenesisTβ4 raises VEGF indirectly by stabilizing HIF-1α protein; in ischemic-limb mice it also increased Ang2, Tie2, and Notch signaling, and blocking Notch or NF-κB reversed the resulting gains in capillary density.
- NF-κB Suppression in Inflamed EpitheliumIn TNF-α-challenged corneal epithelial cells, Tβ4 blocked p65 phosphorylation and nuclear translocation; a phase III keratopathy trial found a healing benefit reaching significance only after dosing stopped.
- Progenitor Mobilization & Ac-SDKP CleavageTβ4 drove epicardial explant outgrowth into vascular and fibroblast lineages in mice; its cleavage product Ac-SDKP reduced lung collagen in bleomycin-treated mice and sped hair-follicle stem cell migration in rats.
Section 04
Dosage Information
Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES| Route / system | Context | Range studied | Limitation |
|---|---|---|---|
| Topical — eye drops | Phase 3 trials — corneal nerve damage and dry eye | 0.1% drops (1 mg/mL) five times a day for 28 days; in dry eye, 0.05% and 0.1% four times a day for 28 days | The fullest human data here is a drop in the eye, and the drug is approved nowhere: 18 people in one trial; the 700-person dry eye trial missed its goals. |
| Intravenous — healthy volunteers | Phase 1 safety study, single dose then 14 days | 42, 140, 420 and 1260 mg — roughly 0.5–18 mg/kg for a 70–90 kg adult; each dose once, then daily for 14 days | Ten healthy people per dose group, and only safety was measured: it shows the range was tolerated and names a working dose for nothing. |
| Intravenous — after a heart attack | Heart trials; the phase 2 was withdrawn before dosing | The withdrawn protocol: 450 or 1200 mg daily for 3 days, then weekly for 4 weeks. Newer trials give 0.5–20 µg/kg daily for 7 days. | Milligrams against micrograms, and neither is an answer: the milligram trial never enrolled a patient, and the microgram trials have not reported. |
| Topical — wound gel | Phase 2 — bedsores and leg ulcers from poor circulation | Gel at 0.01%, 0.02–0.03% and 0.1% on the ulcer for up to 84 days; 72 patients in the leg ulcer trial | The doses did not line up: 33% healed on the middle strength against 24% on placebo, and the highest did worse than both. None can be called effective. |
| Subcutaneous — self-administration | Vials sold as thymosin beta-4, outside any trial | Practice copies TB-500, with no trial dose here: 2–5 mg twice weekly for 4–6 weeks, then 2–2.5 mg weekly — 22–71 µg/kg at 70–90 kg | No human study has injected full-length Tβ4 under the skin, and much sold under this name is TB-500, a seven-amino-acid fragment of a different weight. |
Results
Syringe Fill Level (100u syringe)
Set positive values for: Recommended dose per kg.
Research Use Only. This information is for educational and research purposes only. Not intended for medical advice or self-medication.
Section 05
Protocols
No protocols featuring this peptide yet. Browse All Protocols
Section 06
Stability & Storage
Lyophilised powder
Supplied as a lyophilised powder and kept at −20 °C for long-term stability. The N-terminal acetylation protects it against aminopeptidase degradation. It is reconstituted with bacteriostatic water.
After reconstitution
The reconstituted solution is stored at 2–8 °C and used within 21 days. The peptide's methionine residue remains susceptible to oxidation.
Section 07
Side Effects & Precautions
Generally well-tolerated in clinical trials. Mild injection site reactions. Transient lightheadedness. Theoretical cancer concern due to pro-migratory and pro-angiogenic properties, though no evidence from clinical studies. Limited long-term human safety data.
Section 08
Regulatory Status
The two are tracked separately by the FDA: TB-500 has a live compounding review, while the natural peptide's clinical programme ran — and stalled — through ordinary drug channels.
FDA / United States
Not approved, either form
Neither natural Thymosin Beta-4 nor the TB-500 fragment has cleared FDA approval; RegeneRx pursued the natural peptide through the standard IND pathway (RGN-259, RGN-352), while TB-500 was not on the 503A Bulks List as of 5 August 2026, so pharmacies have no lawful route to compound it.
TB-500 (FDA review)
A committee recommended easing that limit
On 23 July 2026 the Pharmacy Compounding Advisory Committee voted 8 to 6 to add TB-500 — not full-length Thymosin Beta-4 — to the 503A Bulks List; the vote doesn't bind FDA, and the list changes only through formal rulemaking, not complete as of this check.
WADA
Prohibited under category S2
Thymosin Beta-4 and its fragment TB-500 are both named explicitly under Peptide Hormones, Growth Factors, Related Substances and Mimetics — banned at all times, in and out of competition.
Clinical trials
Phase 3 tried and missed twice
RegeneRx's ophthalmic analogue RGN-259 failed to meet co-primary endpoints in both the US ARISE dry-eye trials and the European SEER-3 neurotrophic-keratitis trial; the cardiac analogue RGN-352 has only early-phase IND data.
The fragment sold online as «TB-500» carries its own separate FDA review; neither it nor the natural peptide is close to approval. Regulatory status differs between jurisdictions and changes over time — check the current documents of your own regulator and sport authority before relying on any of this.
Section 09
Research Studies
- [1]Structural basis of actin sequestration by thymosin-β4: implications for WH2 proteinsIrobi E, Aguda AH, Larsson M, Guerin C, Yin HL, Burtnick LD, Blanchoin L, Robinson RC. · The EMBO Journal · 2004
- [2]The β-thymosin/WH2 domain: structural basis for the switch from inhibition to promotion of actin assemblyHertzog M, van Heijenoort C, Didry D, Gaudier M, Coutant J, Gigant B, Didelot G, Préat T, Knossow M, Guittet E, Carlier MF. · Cell · 2004
- [3]The actin binding site on thymosin β4 promotes angiogenesisPhilp D, Huff T, Gho YS, Hannappel E, Kleinman HK. · The FASEB Journal · 2003
- [4]Thymosin β4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repairBock-Marquette I, Saxena A, White MD, DiMaio JM, Srivastava D. · Nature · 2004
- [5]Thymosin β4 induces the expression of vascular endothelial growth factor (VEGF) in a hypoxia-inducible factor (HIF)-1α-dependent mannerJo JO, Kim SR, Bae MK, Kang YJ, Ock MS, Kleinman HK, Cha HJ. · Biochimica et Biophysica Acta - Molecular Cell Research · 2010
- [6]Thymosin-β4 induces angiogenesis in critical limb ischemia mice via regulating Notch/NF-κB pathwayLv S, Cai H, Xu Y, Dai J, Rong X, Zheng L. · International Journal of Molecular Medicine · 2020
- [7]Angiopoietin-1/Tie2 signaling pathway contributes to the therapeutic effect of thymosin β4 on diabetic peripheral neuropathyWang L, Chopp M, Szalad A, Lu X, Lu M, Zhang T, Zhang ZG. · Neuroscience Research · 2019
- [8]Thymosin beta 4 suppression of corneal NFκB: a potential anti-inflammatory pathwaySosne G, Qiu P, Christopherson PL, Wheater MK. · Experimental Eye Research · 2007
- [9]0.1% RGN-259 (thymosin β4) ophthalmic solution promotes healing and improves comfort in neurotrophic keratopathy patients in a randomized, placebo-controlled, double-masked phase III clinical trialSosne G, Kleinman HK, Springs C, Gross RH, Sung J, Kang S. · International Journal of Molecular Sciences · 2022
- [10]Thymosin β4 induces adult epicardial progenitor mobilization and neovascularizationSmart N, Risebro CA, Melville AAD, Moses K, Schwartz RJ, Chien KR, Riley PR. · Nature · 2007
- [11]Prolyl oligopeptidase is involved in release of the antifibrotic peptide Ac-SDKPCavasin MA, Rhaleb NE, Yang XP, Carretero OA. · Hypertension · 2004
- [12]Preventive and therapeutic effects of thymosin β4 N-terminal fragment Ac-SDKP in the bleomycin model of pulmonary fibrosisConte E, Fagone E, Gili E, Fruciano M, Iemmolo M, Pistorio MP, Impellizzeri D, Cordaro M, Cuzzocrea S, Vancheri C. · Oncotarget · 2016
- [13]Thymosin β4 increases hair growth by activation of hair follicle stem cellsPhilp D, Nguyen M, Scheremeta B, St-Surin S, Villa AM, Orgel A, Kleinman HK, Elkin M. · The FASEB Journal · 2004
- [14]Thymosin β4 accelerates wound healingMalinda KM, Sidhu GS, Mani H, Banaudha K, Maheshwari RK, Goldstein AL, Kleinman HK. · Journal of Investigative Dermatology · 1999
- [15]Muscle injury-induced thymosin β4 acts as a chemoattractant for myoblastsTokura Y, Nakayama Y, Fukada S, Nara N, Yamamoto H, Matsuda R, Hara T. · Journal of Biochemistry · 2011
Section 10
Frequently Asked Questions
Clinical trials have run in dermal wounds and corneal injuries. In one phase 2 venous leg-ulcer trial, a middle-strength gel (0.02 to 0.03%) healed 33% of ulcers against 24% on placebo, but the highest strength tested did worse than both — a pattern that does not show a clean dose-response and stops short of establishing that the drug works.
Not in humans, so far. The only completed human trial tested safety and pharmacokinetics in healthy volunteers, not heart-attack patients, and a planned phase 2 efficacy trial in acute heart attack was withdrawn in 2021 before anyone was enrolled. Reduced infarct size and improved heart function are findings from animal studies only.
Not exactly. Thymosin beta-4 is the full 43-amino-acid, roughly 5 kDa native peptide. Much of what is sold as TB-500 is instead a synthetic 7-amino-acid fragment of it, a different and much smaller molecule. No human study has injected the full-length peptide under the skin, so the trial dosing data for one does not carry over to the other.
Phase 1 volunteers received single intravenous doses from 42 to 1,260 mg, then daily dosing for 14 days, purely to test safety. Eye-drop trials used 0.05 to 0.1% solution, four to five times a day. Self-administered subcutaneous use copies TB-500 practice at 2 to 5 mg, a dose that has never been tested for the full-length peptide in any trial.
It has been generally well tolerated in the trials run so far, with mild injection-site reactions and occasional lightheadedness. Because it promotes cell migration and blood vessel growth, there is a theoretical concern about tumor growth, but no clinical study has reported evidence of it, and long-term human safety data are still limited.
It has not been approved by the FDA for any use and remains investigational, with completed phase 2/3 trials only in eye and cardiac applications. WADA prohibits it under category S2, growth factors, so it is banned in and out of competition for tested athletes.
This depends on which trial you look at, since none was designed to measure onset speed. Eye-drop trials assessed outcomes at 28 days, and wound-gel trials at up to 84 days. No study has tracked when an effect begins, and no data at all exist for the self-administered subcutaneous use most people ask about.