Peptide / SubQ / 2-5mg 2x per week

TB-500 / TB4*

Thymosin beta-4 was isolated from calf thymus and named as a thymic hormone, then reclassified a decade later as the main actin-sequestering peptide of the cell. TB-500 is not that protein but a seven-residue piece of it, and it reached animals and people through veterinary preparations and online sellers, with pharmacy compounding a third route that the US regulator reviewed and flagged as a possible safety risk rather than approved.

In plain words

TB-500 is the name sold for a seven-amino-acid piece cut out of thymosin beta-4, a protein present in nearly every cell that helps organize the cell's internal scaffolding, and people buy it hoping it will speed up healing. The honest starting point is that no published human study has ever given anyone the molecule sold as TB-500. The three human studies on record used the whole 43-amino-acid parent protein instead, given into a vein or as eye drops, not the short fragment injected under the skin that is actually sold; the closest published result for the fragment itself is a single pair of laboratory dish and tissue experiments. Animal work with the parent protein did speed wound closure in rats and improve heart function in mice, but bench work also showed that the parent uses two separate structural parts to do that job and the fragment carries only one of them, which is a concrete reason not to assume the parent's results carry over. It is not authorized as a medicine anywhere and is on the prohibited lists of racing, equestrian and anti-doping authorities. The honest summary of its safety is neither safe nor unsafe but that nobody has looked, and because sellers offer either molecule under the one name, a vial with this label may not even contain the fragment.

At a glance

Half-life	0.1 days
Tmax	0.03 days
Route(s)	SubQ
Published dosing range	2-5mg 2x per week
Vial strengths	5, 2, 10 mg

Reference data from the DosePlot canon -- not a protocol recommendation.

Serum curve

Single 3.5 mg dose by SubQ, rendered from the same engine that powers the interactive chart. Relative levels, not lab values.

Chart this compound

What does the evidence show?

Two things are labeled separately here because they answer different questions. The tier is how a study was built. The distance chips are whether that study touched this molecule, by this route, in a population resembling the reader. A randomized trial of a different molecule keeps its tier and still says nothing about this compound.

Finding	Tier	Distance from use	Study
Intravenous thymosin beta-4 was well tolerated in a randomized, placebo-controlled Phase 1 study. Four cohorts of ten healthy adults each received a single dose of placebo or synthetic peptide at 42, 140, 420, or 1260 mg, then the same regimen daily for 14 days. Adverse events were infrequent and mild to moderate, with no dose-limiting toxicity and no serious adverse events. Single-dose kinetics were dose proportional, and half-life rose as the dose rose. This was the full 43-residue protein given intravenously, not the seven-residue fragment sold as TB-500.Full-length 43-residue thymosin beta-4, given intravenously to healthy adults. The product sold as TB-500 is a seven-residue acetylated fragment injected under the skin.	rct	molecule: differentroute: differentpopulation: same	Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers.Annals of the New York Academy of Sciences 1194:223-229, 2010
Thymosin beta-4 eye drops improved severe dry eye in a randomized, double-masked, vehicle-controlled Phase 2 trial. Nine patients with severe dry eye were randomized to either 0.1 percent drops or vehicle control, six times daily for 28 days, within a 56-day study. Results are reported by eye: at day 56 the treated group (12 eyes) showed a 35.1 percent reduction in ocular discomfort compared with vehicle control (6 eyes) (P = 0.0141) and a 59.1 percent reduction in total corneal fluorescein staining (P = 0.0108). Twelve treated eyes is about six patients, so nine is the randomized total and not the number who received the peptide. The authors describe the trial as small. Topical, and again the full-length protein.Full-length protein as eye drops, in patients with severe dry eye. Neither the molecule, the route, nor the tissue matches injected use of the fragment.	rct	molecule: differentroute: differentpopulation: different	Sosne G, Dunn SP, Kim C. Thymosin beta4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial.Cornea 34(5):491-496, 2015
Nine patients aged 37 to 84 with chronic nonhealing neurotrophic corneal epithelial defects were treated with thymosin beta-4 eye drops for 28 or 49 days under compassionate use. The six with geographic defects healed; the three with punctate defects did not change; one developed stromal thinning. There was no control group, no blinding, and no randomization.Full-length protein as eye drops, in patients with nonhealing corneal defects, uncontrolled and unblinded.	clinical	molecule: differentroute: differentpopulation: different	Dunn SP, Heidemann DG, Chow CY, et al. Treatment of chronic nonhealing neurotrophic corneal epithelial defects with thymosin beta4.Annals of the New York Academy of Sciences 1194:199-206, 2010
The seven-residue actin-binding peptide matched the whole protein in two angiogenesis assays. Using natural thymosin beta-4, proteolytic fragments, and synthetic peptides, the parent and the seven-residue motif showed near-identical activity at about 50 nM in human endothelial cell migration and in chick aortic arch sprouting, while peptides missing any part of the motif were inactive. This is the closest thing to direct evidence for the molecule sold as TB-500, and it is a cell and tissue assay, not an animal or human outcome.The seven-residue actin-binding motif itself, which is the sequence sold as TB-500, but the report does not describe it as acetylated at the amino terminus, and the acetyl cap is what defines the marketed product. Cells and excised tissue, so no route applies. This is the closest published result to the marketed molecule.	preclinical	molecule: relatedroute: n/apopulation: different	Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. The actin binding site on thymosin beta4 promotes angiogenesis.FASEB Journal 17(14):2103-2105, 2003
Actin binding by the parent protein uses two separate structural elements, and the fragment carries only one of them. Mutational analysis of synthetic full-length variants mapped the interaction to an N-terminal segment (residues 1-16), which must fold into an alpha-helix and contributes a hydrophobic patch at Met6, Ile9 and Phe12 plus an electrostatic contact at Lys14, and to a hexapeptide motif at residues 17-22 contributing a contact at Lys18. A peptide spanning only residues 17-23 keeps the second element and drops the first.Synthetic full-length variants, mapped in vitro. Relevant to the fragment only as the reason to expect it behaves differently: it keeps one of the two structural elements the parent uses to bind actin.	preclinical	molecule: relatedroute: n/apopulation: different	Van Troys M, Dewitte D, Goethals M, Carlier MF, Vandekerckhove J, Ampe C. The actin binding site of thymosin beta 4 mapped by mutational analysis.The EMBO Journal 15(2):201-210, 1996
In a rat full-thickness wound model, thymosin beta-4 applied topically or given intraperitoneally increased reepithelialization by 42 percent at 4 days and by as much as 61 percent at 7 days over saline controls, with at least 11 percent more wound contraction by day 7 and more collagen deposition and new vessel growth. Keratinocyte migration in a Boyden chamber rose two to three fold with as little as 10 pg of peptide. Full-length protein, in rats.Full-length protein, applied topically or into the abdominal cavity, in rats.	preclinical	molecule: differentroute: differentpopulation: different	Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta4 accelerates wound healing.The Journal of Investigative Dermatology 113(3):364-368, 1999
Thymosin beta-4 formed a complex with PINCH and integrin-linked kinase and activated Akt. After coronary artery ligation in mice, treatment raised integrin-linked kinase and Akt activity in the heart, improved early myocyte survival, and improved cardiac function. This animal result is what pushed the compound into human drug development, and it used the whole protein.Full-length protein, in mice, after surgical coronary artery ligation.	preclinical	molecule: differentroute: differentpopulation: different	Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair.Nature 432(7016):466-472, 2004
Community protocols converge on 2-5 mg subcutaneously twice a week, usually a higher loading phase for four to six weeks followed by a lower maintenance dose, matching the range DosePlot's reference record carries for this compound. Nothing in the published human record stands behind that schedule. The three published human studies all used the full-length 43-residue protein, none of them by subcutaneous injection, so the dosing rests on animal work with a different molecule and on self-report.Molecule, route and population all match how the marketed product is actually used. No study stands behind it.	anecdotal	molecule: sameroute: samepopulation: same	community reports aggregated from reddit, MESO-Rx, and similar forumsno study

What the published record supports

No published human study has administered the molecule sold as TB-500. The three published human studies used the full 43-residue parent protein, by intravenous infusion or as eye drops; the marketed product is a seven-residue acetylated fragment injected under the skin. The closest published result for the fragment sequence is a single pair of cell and tissue assays, and the only description of the product as people actually use it is uncontrolled self-report.

What it supports

That the PARENT protein is tolerated intravenously over two weeks. Forty healthy adults received 42 to 1260 mg daily with no dose-limiting toxicity and no serious adverse events. This is real human safety data, and it is about a different molecule by a different route.
That the seven-residue motif carries angiogenic activity in vitro. In endothelial cell migration and chick aortic arch sprouting it matched the parent at about 50 nM, and peptides missing part of the motif were inactive. This is the only published result obtained with the marketed sequence.
That the parent protein speeds wound closure in rats and improves cardiac function in mice after coronary ligation. Animal outcomes, parent molecule.
That the two molecules are not interchangeable on the bench. Actin binding in the parent uses two structural elements, and the fragment carries only one of them.

What it cannot support

That TB-500 helps any human injury, at any dose, by any route. Nothing in the human record was obtained with it.
That results from the parent protein transfer to the fragment. The one in-vitro match is a single assay pair, and the mapping work gives a specific structural reason to expect divergence in a body.
That TB-500 is unsafe. No human exposure data exists for the fragment, and absence of data is not evidence of harm any more than it is evidence of safety. The honest statement is that nobody has looked.
That a vial labeled TB-500 contains the fragment. Vendors claim either molecule under the one name, and no regulator has authorized either.

Never measured

Human pharmacokinetics of the fragment: absorption, half-life, distribution, or clearance after subcutaneous injection. None published.
Any dose-response in a person. The community schedule of 2 to 5 mg twice weekly has no published basis in humans at all.
Exposure beyond two weeks. The longest human dosing on record is 14 days, of the other molecule.
Whether the acetyl cap that defines the product survives in circulation, and what the fragment is broken down into.

How did it get here?

preclinical1981: Low, Hu and Goldstein report the complete amino acid sequence of thymosin beta-4 purified from calf thymus: 43 residues, acetylated at the front. It is called a thymic hormone because it induces terminal deoxynucleotidyl transferase activity in thymocyte populations. The same sequence is later found in humans.
preclinical1991: Safer, Elzinga and Nachmias show that thymosin beta-4 and Fx, the major actin-sequestering peptide of platelets and other cells, are indistinguishable. The thymic hormone turns out to be an abundant intracellular cytoskeletal protein present in essentially every cell. Reference databases still carry Fx as an alternate name for it.
preclinical1996-2004: The molecule gets taken apart. Van Troys and colleagues map actin binding to two separate structural elements, an N-terminal helix and a hexapeptide at residues 17 to 22. Malinda shows the full protein speeds wound closure in rats. Philp shows the short actin motif on its own reproduces the angiogenic activity. A Nature paper on cardiac repair after coronary ligation in mice moves the full protein toward the clinic.
first-human2010-2015: The human program runs entirely on the 43-residue protein. Forty healthy adults receive placebo or the peptide intravenously at 42 to 1260 mg, daily for two weeks, in a Phase 1 safety study. Nine patients with nonhealing corneal defects receive it as eye drops under compassionate use. A nine-patient Phase 2 trial in severe dry eye meets its endpoints. Nothing is approved, anywhere.
grey-market2012: While the human program on the parent protein is still running, two doping-control laboratories establish what is actually being sold. A Ghent group identifies N-terminally acetylated LKKTETQ, the 17-23 fragment of human thymosin beta-4, in TB-500 material using high-resolution mass spectrometry. A Hong Kong racing laboratory describes TB-500 as an emerging veterinary preparation, publishes a method for the peptide and its metabolites in equine urine and plasma, and reports what it calls the first identification of TB-500 and its metabolites in post-administration samples from horses, after a single dose containing 10 mg of the acetylated peptide. The marketed product is the fragment, not the protein the human trials used.
grey-market2025-2026: Thymosin beta-4 is prohibited by the IFHA, the FEI and WADA, and products sold online claim either the acetylated fragment or the whole protein. A French racing laboratory publishes the first baseline blood concentrations in racehorses and shows why the obvious test fails: the peptide is endogenous, and its measured level climbs in a blood tube left unseparated as cells break open. Detection has to key on a synthesis impurity the animal cannot make. A second supply route runs through pharmacies. The US Food and Drug Administration lists Thymosin beta-4, fragment (LKKTETQ), also known as TB-500, among bulk substances nominated for use in compounding that it placed in the category presenting significant safety risks, states that it has identified no human exposure data for drug products containing the fragment, and records the nomination as later withdrawn by its nominator.

How is it made?

Production happens in three stages.

1. Building the chain. The peptide sold as TB-500 is seven residues long, assembled by solid-phase peptide synthesis. The C-terminal glutamine is anchored to a resin bead, and the other six residues are added one at a time, each cycle unmasking the growing end and coupling the next protected residue. Six couplings is a short run by peptide standards; the two lysines stay side-chain protected throughout. The protein this sequence is copied out of is 43 residues, a far longer and more expensive synthesis, and both are sold under the same name.

2. Capping and cleaving. The finished chain is deliberately acetylated at its free amino end. That cap defines the product: acetylated LKKTETQ is what analytical laboratories have identified in actual TB-500 material, and the uncapped peptide is a different substance. Strong acid then releases the chain from the resin and strips the side-chain protecting groups in one step. The crude peptide is precipitated and separated from deletion products by reversed-phase chromatography, with identity confirmed by high-resolution mass spectrometry.

3. Filling the vial. The purified peptide is dissolved, sterile-filtered, dispensed, and freeze-dried to a white cake, then sealed and stored cold. Sterile fill and batch testing are what vary outside regulated manufacturing. This compound adds a second variable: the name does not fix the molecule. Products sold online claim either the acetylated fragment or the whole protein, and no regulator has authorized either, so nothing official stands behind the claim.

Worth knowing

The name records a mistaken address. Thymosin beta-4 was named for the thymus and classed as a hormone, and ten years later Safer and colleagues showed it was indistinguishable from Fx, the actin-sequestering peptide already known from platelets. It is neither thymic nor a hormone but one of the most abundant proteins inside ordinary cells. Sequence databases still list Fx as an alternate name for the human protein, which is the fossil of the reclassification.

Safer D, Elzinga M, Nachmias VT. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable.The Journal of Biological Chemistry 266(7):4029-4032, 1991

Racing laboratories cannot test for thymosin beta-4 by measuring thymosin beta-4. The peptide is endogenous, highly conserved across mammals, and abundant inside cells, so a blood tube left unseparated grows a rising apparent concentration as the cells lyse, and a mishandled sample reads like an administered dose. A 2025 population study of racehorse blood found baseline levels did not vary meaningfully with sex, age, or breed, and concluded that the workable approach is detecting a non-natural synthesis impurity, a molecule the animal has no way to make.

Delcourt V, Garcia P, Chabot B, et al. Equine doping controls of thymosin beta 4: a population study and strategy for misuse detection.Drug Testing and Analysis 17(7):1071-1077, 2025

The clinical literature has stopped treating the two as one entry. A 2026 sports-medicine review of peptides marketed direct to patients lists thymosin beta-4 and TB-500, the thymosin beta-4 fragment, as separate entries in the same review, alongside BPC-157, AOD-9604 and CJC-1295. Its summary judgment on the unapproved group is that favorable tissue-repair results in animal models are common and rigorous human safety data are scarce.

Mendias CL, Awan TM. Safety and efficacy of approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance.Sports Medicine 56(8):1921-1935, 2026

Reconstitution

TB-500 / TB4* ships lyophilized and is mixed before use; the published vial strengths are 5, 2, 10 mg. The water volume you add sets the concentration, not the dose -- the calculator turns a vial size and a water volume into mg/mL, draw volume, and units on an insulin syringe.

Open in the reconstitution calculator

Written and reviewed by Evan Marlow, developer of DosePlot · Updated 2026-08-27

Not medical advice. DosePlot is an informational tool, not a healthcare provider, and using it creates no provider-patient relationship. Do not start, stop, or change any protocol without the approval of a licensed healthcare professional.

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