TB-500

A synthetic N-acetylated fragment associated with thymosin beta-4.

Preclinical-heavyPeptide research profile

Also known as: Ac-LKKTETQ, Thymosin beta-4 fragment

Sources reviewed October 1, 2026 (how we review)

Dosing & scaling, explained

The 1-2 mg entries summarize source-library conventions; they are not supported by a validated human TB-500 dosing program. This is educational source context, not a protocol or recommendation.

How sourced amounts are organized

Starting pointNot clinically establishedNo validated titration window
There is no regulator-approved starting dose for this research use. A low-looking number is not automatically safe.
Recorded preset1-2 mg per administrationCalculator library reference
This is the range represented in the in-app protocol library. It describes the source record; it does not validate the regimen.
Higher exposureAbove 2 mg is not characterizedRisk and uncertainty increase
Higher exposure is not established as more effective. Human pharmacokinetic and long-term safety data may be absent.

Drug amount and device markings are different quantities. The calculator converts mass into volume, syringe units, or pen clicks.

Patterns described in source material

Every 3 days to twice monthly in presets
The cadence represented by the recorded calculator presets.
Full-length Tβ4 studies use different formulations
Published experiments may use a different route, formulation, timing, or population and should not be treated as interchangeable.
No universal schedule
No single schedule has been validated across products or research contexts.

Clinical context

No randomized human dose-ranging trial establishes systemic TB-500 exposure, schedule, or long-term safety.

Storage, handling and interpretation

Lyophilized material

Keep cold, dry, and protected from light according to the manufacturer certificate or validated lab SOP.

After reconstitution

Use sterile technique, refrigerate as validated, and avoid repeated freeze-thaw cycles.

Traceability

Record lot, concentration, preparation date, and the identity/purity documentation used by the lab.

Reported protocols for TB-500

What published studies and recent community write-ups report about amounts, timing and course length. 4 clinical, 3 preclinical and 3 community-reported rows, each linked to its source. These are descriptions of what others report, not instructions, and nothing here is medical advice.

Context	Dose	Frequency	Route	Course	Source
Clinical4 rows
Phase 1 intravenous thymosin beta-4 in healthy volunteers (full-length protein)40 healthy adults in four cohorts of 10	42, 140, 420 or 1,260 mg	Single dose, then the same dose once daily for 14 days	Intravenous	14 daysNot applicable	Annals of the New York Academy of Sciences (PubMed)2010
Adverse events were infrequent and mild to moderate, with no dose-limiting toxicity or serious events across a 30-fold dose range, and single-dose pharmacokinetics were dose proportional with a half-life that lengthened at higher doses. This is the only systemic human dosing study of thymosin beta-4 and it used the 43-residue protein, not the TB-500 fragment.
Phase 2 topical gel for pressure ulcers (RGN-137, full-length protein)72 adults aged 19-85 with a stable stage III or IV pressure ulcer of 5-70 cm2	0.01%, 0.02% or 0.1% thymosin beta-4 gel	Once daily	Topical to the wound	Up to 84 daysNone	ClinicalTrials.gov2008
The gel was safe and well tolerated at every strength, which was the primary objective, but none of the three concentrations differed significantly from placebo on complete healing or healing rate. The sponsor reported that the 0.02% strength started healing sooner without reaching significance.
Phase 3 ARISE-3 eye drops for dry eye (RGN-259, full-length protein)700 adults with dry eye syndrome at 20 US sites	0.1% thymosin beta-4 preservative-free ophthalmic solution, one drop per eye	Four times daily	Topical to both eyes	14 daysNone	ClinicalTrials.gov2021
The trial missed its primary sign and symptom endpoints; a prespecified secondary symptom, ocular grittiness, improved significantly at one and two weeks. ARISE-1, -2 and -3 together have produced scattered significant findings but no approval, and the product remains investigational.
Phase 3 SEER-1 eye drops for neurotrophic keratopathy (RGN-259, full-length protein)18 adults with stage 2 or 3 neurotrophic keratopathy (10 treated, 8 placebo)	0.1% thymosin beta-4 (timbetasin acetate) ophthalmic solution	Five times daily	Topical to the eye	4 weeks, with follow-up to day 43None	International Journal of Molecular Sciences (PubMed Central)2023
Complete healing of the epithelial defect at 4 weeks occurred in 6 of 10 treated patients versus 1 of 8 on placebo, a trend that did not reach significance (p = 0.0656), with a significant difference at day 43 and no safety signals. Eighteen patients, with an older placebo group that started with larger defects, is far too few for a definitive result.
Preclinical3 rows
Preclinical rat full-thickness wound model (full-length protein)Rats with 8 mm dorsal punch wounds	5 mcg in 50 mcL topically per wound; 60 mcg in 300 mcL intraperitoneally	Topical at wounding and again at 48 hours; intraperitoneal at wounding and every other day	Topical or intraperitoneal	7 daysNot applicable	Journal of Investigative Dermatology (PubMed)1999
Both routes increased re-epithelialization by 42% at day 4 and about 61% at day 7 compared with saline, with more wound contraction, collagen deposition and new vessels. The experiment used three rats per condition and the whole 43-residue peptide.
Preclinical aged and diabetic mouse wounds, including the LKKTETQ fragmentdb/db diabetic mice and 26-month-old aged mice with full-thickness dermal wounds	Thymosin beta-4 or the LKKTETQ heptapeptide at 0.01% (5 mcg in 50 mcL) per wound	At wounding and again at 48 hours	Topical in saline or a hydrogel	8 days of observationNot applicable	Wound Repair and Regeneration (PubMed)2003
The seven-residue actin-binding fragment promoted repair in aged mice to a degree comparable with the parent molecule, which is the origin of the TB-500 concept. This is the closest published evidence for the fragment itself, and it involved two topical applications to a skin wound rather than systemic injection.
Preclinical cell and tissue assays of the actin-binding motifHuman umbilical vein endothelial cells and chick aortic arch explants	About 50 nM of thymosin beta-4 or the seven-residue motif	Single exposure in culture	In vitro	Hours to days in cultureNot applicable	FASEB Journal (PubMed)2003
The intact peptide and the seven-amino-acid actin-binding motif produced near-identical endothelial migration and vessel sprouting at about 50 nM, while peptides missing any part of the motif were inactive. Culture-dish activity establishes which part of the molecule works, not what dose would do anything in a person.
Community-reported3 rows
Community loading and maintenance protocol	2-2.5 mg	Twice weekly for 4-6 weeks (loading), then once weekly (maintenance)	Subcutaneous from a 10 mg vial reconstituted in 2 mL (5 mg/mL; 0.4-0.5 mL or 40-50 units per dose)	4-6 weeks of loading plus 6-8 optional weeks of maintenancePause and re-evaluate after the loading phase in some plans	Community resource2026
This 2026 guide describes the two-phase schedule that circulates in the research-chemical community and states that it has not been validated in any human trial of the fragment. It also records that the FDA's compounding committee reviewed TB-500 in July 2026 and that the compound is not approved.
Vendor-affiliated protocol with a 12-week cap and BPC-157 stack	2.5 mg (5 mg vial in 1 mL, 0.5 mL per draw); 5 mg twice weekly described as an unsupported higher load	Twice weekly (for example Monday and Thursday) for 4-6 weeks, then once weekly for 4-8 weeks	Subcutaneous, with intramuscular described as an alternative	Up to 12 weeks totalStop at 12 weeks; the guide cites anti-thymosin antibodies in long animal exposures as its reason	Community resource2026
A vendor-affiliated 2026 article pairs 2.5 mg weekly TB-500 with 250-500 mcg daily BPC-157 for 4 weeks and argues the loading phase should match the first six weeks of tissue repair. It admits that the rodent studies behind the rationale ran 14-28 days and that there are no human trials, and it mislabels the fragment as 17 amino acids, an example of how loosely the term TB-500 is used.
Monograph table of community dose tiers	2-2.5 mg (standard loading); 2-4 mg per week (maintenance); 5-10 mg per week (aggressive); 1.5 mg reported as a minimum	Twice weekly loading; once or twice weekly maintenance; 2-3 times weekly in aggressive plans	Subcutaneous	4-6 weeks loading; 6-8 weeks total in the 2026 cycling pattern4 or more weeks off, increasingly favored over continuous use	Community resource2026
This monograph marks every subcutaneous injection row as having no human validation and sets them beside the real thymosin beta-4 trials, which used eye drops, wound gel or intravenous infusion. Its 2026 update notes that community practice has stabilized, that cycling is emphasized over continuous dosing, and that some users report results at 1.5 mg twice weekly.

How a course is commonly described

Weeks 1-6: loadingCommunity-reported
Community protocols describe 2-2.5 mg subcutaneously twice a week, often on fixed days, for 4-6 weeks, about 4-5 mg per week. Guides describe this as building systemic levels during the active repair window, a rationale borrowed from rodent wound models rather than any human data.
Weeks 7-12: maintenanceCommunity-reported
The dose drops to 2-2.5 mg once a week for a further 4-8 weeks, or the course ends after loading. One guide caps the whole course at 12 weeks and cites antibody formation in long-duration animal studies as its reason, a concern that has not been examined for the fragment in humans.
BreakCommunity-reported
A break of at least 4 weeks after a 6-8 week course is the pattern described in 2026, with continuous dosing falling out of favor and some users testing lower 1.5 mg doses. No source gives a tested reason for the length of the break.
Clinical comparison: full-length thymosin beta-4Clinical
Every human study used the 43-residue protein: 42-1,260 mg intravenously once daily for 14 days in healthy volunteers, 0.01-0.1% gel once daily for up to 84 days on ulcers, and 0.1% eye drops four or five times a day for 2-4 weeks. The two phase 2 ulcer trials were reported to shorten healing by nearly a month only among patients who healed, and no study has used a subcutaneous twice-weekly schedule.
Regulatory checkClinical
The FDA's 2026 review for the compounding committee found no article in which TB-500 had been given to humans, noted that vendors use the names TB-500 and thymosin beta-4 interchangeably although they are different substances, and recorded that the nominated product was a 3 mg/mL powder for subcutaneous or intramuscular injection. The committee's favorable vote is advisory and FDA reviewers had proposed non-inclusion.

No human study has ever administered the TB-500 heptapeptide by any route, so the loading and maintenance schedule above is entirely community convention. The published rodent work on the fragment consisted of two topical applications to a skin wound.
Vials labeled TB-500 may contain the 889 g/mol fragment or the 4963 g/mol full-length protein, a 5.6-fold difference in molar amount per milligram. The FDA has flagged this naming confusion as a patient safety risk, and only mass spectrometry settles what is in a given vial.
Thymosin beta-4 and its derivatives including TB-500 are prohibited at all times under WADA section S2.3, and validated detection methods exist. The July 2026 advisory committee recommendation does not make TB-500 legal to compound; FDA must still complete notice-and-comment rulemaking.

Sources for this section (14)

FDA Briefing Document: TB-500-related bulk drug substances, Pharmacy Compounding Advisory Committee, July 23, 2026U.S. Food and Drug Administration2026Clinical
A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteersAnnals of the New York Academy of Sciences (PubMed)2010Clinical
Study of Thymosin Beta 4 in Patients With Pressure Ulcers (NCT00382174)ClinicalTrials.gov2008Clinical
The regenerative peptide thymosin beta4 accelerates the rate of dermal healing in preclinical animal models and in patientsAnnals of the New York Academy of Sciences (PubMed)2012Clinical
Assessment of the Safety and Efficacy of RGN-259 Ophthalmic Solutions for Dry Eye Syndrome: ARISE-3 (NCT03937882)ClinicalTrials.gov2021Clinical
RegeneRx Reports Topline Results of ARISE-3 Dry Eye TrialRegeneRx Biopharmaceuticals2021Clinical
0.1% RGN-259 (Thymosin beta4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical TrialInternational Journal of Molecular Sciences (PubMed Central)2023Clinical
Thymosin beta4 accelerates wound healingJournal of Investigative Dermatology (PubMed)1999Preclinical
Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged miceWound Repair and Regeneration (PubMed)2003Preclinical
The actin binding site on thymosin beta4 promotes angiogenesisFASEB Journal (PubMed)2003Preclinical
Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potentialDrug Testing and Analysis (PubMed)2012Preclinical

Plus 3 community resources (dosing guides, forum threads and vendor write-ups), reported above but not linked.

Overview

TB-500 is the trade name under which a synthetic seven-residue fragment of thymosin beta-4, Ac-LKKTETQ (residues 17-23, the actin-binding motif), was identified in a veterinary product aimed at racehorses and greyhounds around 2011. Thymosin beta-4 itself is a 43-amino-acid protein found in nearly every cell, which RegeneRx has tested in people as an intravenous solution, a wound gel (RGN-137) and eye drops (RGN-259), while the fragment has never been given to humans in any published study according to the FDA's 2026 literature search. Research-chemical vendors sell both the fragment and the full protein as TB-500, so a vial's contents cannot be assumed from its label. Thymosin beta-4 and its derivatives including TB-500 are prohibited at all times under section S2.3 of the WADA list, and in July 2026 the FDA's Pharmacy Compounding Advisory Committee voted 8 to 6 to recommend adding TB-500 to the 503A bulks list against the agency reviewers' advice, a recommendation that has no legal effect until FDA completes rulemaking.

What researchers are exploring

These themes describe recurring questions in published research. They are not claims of effectiveness or recommendations for use.

1
Fragment metabolism
Recent analytical work identifies TB-500 metabolites in serum systems and rats.
2
Cell migration
In-vitro wound assays examine the parent fragment and selected metabolites.
3
Thymosin beta-4 repair biology
Full-length Tβ4 literature covers wound, corneal, vascular, and cardiac models.
4
Anti-doping detection
Analytical methods focus on parent peptide and urinary metabolites.

What the current evidence can support

Study models remain visible so laboratory and animal findings are not mistaken for established human outcomes.

In vitro
Direct fragment assay
A 2024 study compared TB-500 and metabolites in fibroblast wound-healing assays.
Animal
Rat metabolism work
The same study characterized metabolites after administration in rats.
Review
Evidence is often conflated
Findings for 43-amino-acid thymosin beta-4 cannot be assigned automatically to the seven-residue TB-500 fragment.

Amounts recorded for TB-500

These amount records are independent from vial strength, reconstitution volume and measuring device. A recorded source is not the same as study backing, and these values are not recommendations.

1
Standard Dose Range · lower endpointSign in for schedule, duration and source context.
300 mcg
2
Lower maintenance recordSign in for schedule, duration and source context.
1 mg
3
Recorded cycleSign in for schedule, duration and source context.
1.5 mg

Chemistry identifiers

Sequence, synonyms and registry identifiers as recorded in PubChem, the National Library of Medicine's open chemistry database. Formula, mass and CAS number are summarized at the top of the page.

Sequence

Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH

Also listed as

TB-500, TB500, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, Thymosin beta-4 fragment (17-23), N-acetylated, UNII QHK6Z47GTG, TB 500 acetate (salt form sold by vendors), HY-P0170, Full-length thymosin beta-4 is a different record: timbetasin, PubChem CID 16132341

InChIKey

ADKDNDYYIZUVCZ-ZQNQAVPYSA-N

Origin / design

N-acetylated LKKTETQ actin-binding region

IUPAC name

(2S)-2-[[(2S,3R)-2-[[(2S)-2-[[(2S,3R)-2-[[(2S)-2-[[(2S)-2-[[(2S)-2-acetamido-4-methylpentanoyl]amino]-6-aminohexanoyl]amino]-6-aminohexanoyl]amino]-3-hydroxybutanoyl]amino]-4-carboxybutanoyl]amino]-3-hydroxybutanoyl]amino]-5-amino-5-oxopentanoic acid

Limitations and unknowns

Important limitations

Direct human efficacy trials of TB-500 are not established.
Full-length thymosin beta-4 and TB-500 are distinct in both chemistry and evidence.
Sport anti-doping rules may prohibit thymosin-beta-4-related substances.
A calculator preset is a recorded research convention, not a recommendation or evidence of clinical benefit.
Identity, purity, sterility, and stability can vary substantially outside regulated manufacturing.
Route, formulation, and population can make results from one study inapplicable to another use.

Sources

2 curated references, each with its journal, year and study model, plus 3 community resources reported but not linked.

Simultaneous quantification of TB-500 and its metabolites and screening by wound-healing activitiesJournal of Pharmaceutical and Biomedical Analysis2024Animal
Thymosin beta 4 accelerates wound healingJournal of Investigative Dermatology1999Animal

How sourced amounts are organized

Patterns described in source material

Storage, handling and interpretation

How a course is commonly described

What researchers are exploring

Fragment metabolism

Cell migration

Thymosin beta-4 repair biology

Anti-doping detection

Direct fragment assay

Rat metabolism work

Evidence is often conflated

Sequence

Also listed as

InChIKey

Origin / design

Important limitations