peptide

TB-500 (thymosin β4 fragment)

A small lab-made piece of the natural protein thymosin beta-4; it has never been tested in people and is not approved anywhere.

A synthetic 7-amino-acid piece of the natural protein thymosin β4; the clinical trials belong to full-length thymosin β4, not to TB-500, which has no genuine human trial of its own and no approval anywhere.

Data refreshed 2026-11-01 · Based on 9 published references

At a glance

FDA approved

No.

Potential results

No study in people has tested TB-500 itself
Full-protein eye drops no better than placebo for dry eye (large trials)
Eye sores healed in 6 of 10 vs 1 of 8 (tiny trial of the full protein)
Stronger tendon healing in rats (animal study only)

Unverified, online reports only: shoulder or hip pain and joint pain, usually alongside BPC-157.

Dose

Study doses: see the Scientific view
Converter: mg, mL and syringe units

Storage

Powder: fridge (2–8 °C) for the short term, freezer (−20 °C) for the long term; after mixing, fridge for up to 28 days (general guidance, not tested for this compound).

A summary of the sources on this page, not medical advice.

What else trials studied for injury, healing and muscle growth: see the research quiz.

Names

Also called: TB500, TB 500, thymosin beta-4 fragment (17-23), Ac-LKKTETQ, Tβ4 (17-23)

Regulatory (US)

FDA approval: none

503A compounding: restricted
Compounding is limited to the circumstances described under Regulatory picture; not a general permission.

Molecule

Formula: C38H68N10O14

MW: 889.0 g/mol

CAS: 885340-08-9

PubChem entry

Sequence: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH (residues 17–23 of thymosin β4, N-acetylated)

Origin

Discovered by: Parent peptide thymosin β4 sequenced by Teresa Low, Shu-Kuang Hu and Allan Goldstein (George Washington University); the originator of the TB-500 fragment is not documented in the literature

Year: 1981

What it is

Thymosin β4 is a small natural protein. It is 43 amino acids long. It is found in almost every cell in the body. Its main job is to hold spare actin. Actin is a protein cells use to build their inner frame and to move. Because of this job, thymosin β4 shows up wherever the body is repairing tissue.

TB-500 is not the same as thymosin β4. It is a lab-made copy of just seven of those 43 amino acids. This short piece (positions 17 to 23) is the part that grabs actin. Sellers often mix up the two names. Some sell the full protein with a TB-500 label.

This matters. Every clinical trial in this article used the full protein, not TB-500. A drug company made it under the code RGN-259 or NL005. No real human study of the seven-amino-acid piece was found. There is one 2026 trial listing that names TB-500. But that listing says it is a made-up example.

Thymosin β4 (Tβ4) is a 43-residue, 4,963 g/mol G-actin-sequestering peptide encoded by TMSB4X, present at high intracellular concentrations and released at wound sites. Its actin-binding motif, LKKTET (residues 17–22), is the basis for TB-500: the synthetic heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ, C38H68N10O14, 889.0 g/mol, CAS 885340-08-9), N-acetylated to slow aminopeptidase cleavage.

Full-length Tβ4 has been reported in preclinical models to promote keratinocyte and endothelial migration, angiogenesis, reduced inflammatory cytokine release, and cardiomyocyte survival after infarction (Goldstein et al., 2005). Whether the isolated 17–23 fragment reproduces those effects is unsettled: some in-vitro and animal work attributes migratory activity to the actin-binding region, while other activities of Tβ4 (for example the N-terminal tetrapeptide Ac-SDKP, a cleavage product with its own biology) reside elsewhere in the molecule. No human pharmacokinetic data for TB-500 have been published.

Who made it and when

Thymosin β4 was first pulled out and mapped in 1981. This was done by Allan Goldstein’s lab at George Washington University. It first came from the thymus gland of calves.

Goldstein later started a company called RegeneRx Biopharmaceuticals. It has run the human trials of the full protein. These include eye drops (RGN-259) for dry eye and for a nerve-damage problem of the clear front of the eye (the cornea). They also include a shot (RGN-352) for heart attack and a gel (RGN-137) for wounds. A Chinese company, Beijing Northland Biotech, is testing its own lab-made version (NL005) after heart attacks.

No one has claimed to have made the TB-500 piece. In science papers and anti-doping papers, it shows up mostly as a product sold by research-chemical sellers. In 2026 a company called Hudson Biotech posted the only trial listing that names it. That listing says it is a made-up example study. So it is not counted as a trial.

Low, Hu and Goldstein published the complete sequence of bovine Tβ4 in PNAS in 1981. RegeneRx (later through the ReGenTree joint venture with HLB Therapeutics for ophthalmology) advanced Tβ4 as RGN-259 (ophthalmic), RGN-352 (systemic injection; a Phase 2 AMI trial was withdrawn) and RGN-137 (dermal gel, Phase 2 in pressure and venous ulcers and epidermolysis bullosa). The fragment’s origin is not documented in peer-reviewed literature; its CAS registration (885340-08-9) and PubChem record exist, but no developer, patent or IND could be verified for it. The only ClinicalTrials.gov record naming the 17–23 fragment, NCT07487363 (Hudson Biotech, posted 2026), states in its own summary that it is “a fictional study” and an example record; this article does not treat it as a trial.

What the data say

For the full protein, human results are mixed. Two large dry-eye trials had about 600 and 700 people. In both, thymosin β4 eye drops did no better than a dummy treatment (placebo) on the main measures.

One very small trial looked at a nerve-damage problem of the cornea. 6 of 10 people on the drops healed fully. Only 1 of 8 on placebo did. A larger follow-up trial is still running. A similar European trial is reported to have missed its main goal.

Wound-healing gels were tested in the 2000s. They were safe but showed only small signs of better healing. A Chinese heart-attack trial ended in 2023. Its results have not been published.

For TB-500 itself, there are no human results of any kind. There is very little animal data on the short piece. Most of what people quote about TB-500 is really data on the full protein.

Full-length Tβ4: ARISE-2 (n=601, 0.1% four times daily, 28 days) and ARISE-3 (n=700, 14 days) did not meet primary endpoints for corneal staining or ocular discomfort. SEER-1 (n=18) reported complete healing of persistent epithelial defects in 60% vs 12.5% at day 29 (p=0.0656), reaching significance at day 43; SEER-2 (n=70 planned) is recruiting. Earlier RGN-137 gel trials (NCT00382174, pressure ulcers, n=72, 0.01–0.1% daily up to 84 days) reported 8 healed on active versus 3 on placebo, a secondary outcome in a safety study. NL005 Phase IIb (NCT05984134, IV 0.5 or 1.0 µg/kg daily for 7 days after PCI) is completed without posted results.

TB-500 fragment: no genuine trial was found. The only registry record naming it, NCT07487363 (a Phase 1/2 design in stable atherosclerotic cardiovascular disease), describes itself as “a fictional study” and discloses no doses. No efficacy, pharmacokinetic or adverse-event data for the fragment have been published. FDA stated in 2023 that it had “not identified any human exposure data” for the fragment.

Regulatory picture

Approval: No product with thymosin β4 or TB-500 is approved anywhere. The full protein is still being tested in company trials. The short piece is not part of any plan for approval.

Pharmacy mixing (compounding): In September 2023 the FDA put the seven-amino-acid piece in Category 2. This is the group of substances the FDA said carry serious safety risks. Pharmacies that mix drugs with it could face FDA action. The FDA said it had found no data at all on people being exposed to it.

By April 2026 the FDA’s page listed it as taken out of that group. The one who first put it forward to the FDA had withdrawn it. In July 2026 an FDA expert panel voted narrowly to advise allowing it for wound healing. That vote does not have to be followed. The FDA had not made a final decision when this was written.

In October 2026, the US health department (HHS) announced a draft policy. It said it does not intend to take enforcement action against licensed pharmacies or doctors who make single-ingredient TB-500 products, as long as they follow set conditions, while the FDA writes its final rule. The policy is not binding, and it is not FDA approval. TB-500 is still not on the official list of allowed ingredients. Comments on the draft are due in mid-November 2026. This page will be updated when a final policy is published.

Sport: The World Anti-Doping Agency (WADA) bans thymosin β4 and its pieces, including TB-500. The ban applies at all times.

Approval: none. Full-length Tβ4 is investigational under RegeneRx/ReGenTree and Northland programmes; that status does not extend to the 17–23 fragment, which has no IND that could be verified.

Compounding: FDA placed “Thymosin beta-4, fragment (LKKTETQ), also known as TB-500” in Category 2 of the interim 503A policy on 2023-09-29, citing aggregation-related immunogenicity, peptide impurities and the absence of human exposure data. The safety-risk page updated 2026-04-22 lists it among substances withdrawn from Category 2 by the nominators. It is not on the 503A bulks list (21 CFR 216.23), so this article records compounding status as restricted. On 2026-07-23 the Pharmacy Compounding Advisory Committee reviewed TB-500 free base and acetate for wound healing and voted narrowly in favour of inclusion; a final FDA rule is required before that changes anything.

On 2026-10-30 HHS published a notice of availability of a draft interim Enforcement Discretion Policy (docket HHS-OASH-2026-0496) covering 503A compounding of TB-500 and five other peptides. HHS states it does not intend to take enforcement action against state-licensed pharmacies, federal facilities or licensed physicians compounding single-active-ingredient products from bulk substance sourced from an FDA-registered manufacturer with a certificate of analysis, dispensed on patient-specific prescriptions with MedWatch adverse-event reporting, pending rulemaking (the list of peptides and these conditions are taken from the Alliance for Pharmacy Compounding’s summary, because the HHS appendices could not be retrieved for this article). The notice says it is not binding and does not add TB-500 to 21 CFR 216.23; 503B outsourcing facilities and products sold for “research use” are outside it. FDA staff had recommended against listing. Comments are due about 2026-11-13; no final policy had been published when this was written.

Anti-doping: thymosin β4 and its derivatives such as TB-500 have been named examples under S2 (peptide hormones, growth factors, related substances and mimetics) of the WADA Prohibited List since 2018.

Dose

Doses reported in trials and studies

How dosing worked in the studies

No human study has tested TB-500 itself. All of them used the full protein, thymosin β4. In ARISE-2 and ARISE-3, 601 and 700 adults with dry eye were assigned by chance to RGN-259 eye drops or a dummy treatment (placebo). They used the drops four times a day. ARISE-2 lasted 28 days and ARISE-3 lasted 14 days. In SEER-1, 18 adults with a nerve-damage problem of the cornea (neurotrophic keratopathy) were assigned by chance to 0.1% drops or placebo. They used them five times a day for 28 days. SEER-2 is testing this against an inactive liquid (vehicle) in a planned 70 adults. In the NL005 Phase IIb trial, 90 adults with a type of serious heart attack (acute anterior STEMI) were assigned by chance to 0.5 µg/kg or 1.0 µg/kg into a vein, or placebo. The first dose came within 12 hours after a procedure to open the blocked artery (PCI). Then they got a dose each day on days 2–7.

Doses used in the studies are in the Scientific view.

Study doses are not personal dosing instructions. Reading doses safely: how concentration and syringe markings work.

Doses reported in studies, exactly as the cited trial reported them. They are not personal dosing instructions. Population, route and schedule matter more than the number.

Trial	Phase	Status	Population	Dose	Result
ARISE-2 (full-length thymosin β4 as RGN-259, not TB-500) NCT02974907	3	Completed	601 adults with dry eye disease of at least 6 months	0.1% RGN-259 ophthalmic solution, one drop in each eye four times daily for 28 days, versus placebo	Neither primary endpoint met: ocular discomfort change 0.07 vs −0.04 placebo, corneal fluorescein staining change 0.07 vs −0.01 placebo at day 29
ARISE-3 (full-length thymosin β4 as RGN-259, not TB-500) NCT03937882	3	Completed	700 adults with dry eye disease	Preservative-free RGN-259 eye drops containing thymosin β4, both eyes four times daily for 14 days, versus placebo	Primary endpoints not met: inferior corneal staining change −0.41 vs −0.46 placebo; ocular discomfort change −0.4 in both arms at day 15
SEER-1 (full-length thymosin β4 as RGN-259, not TB-500) NCT02600429	3	Terminated (business decision; study completion March 2020)	18 adults with stage 2 or 3 neurotrophic keratopathy	0.1% RGN-259 ophthalmic solution five times daily for 28 days, versus placebo	Complete corneal healing at day 29 in 6 of 10 on RGN-259 vs 1 of 8 on placebo (p=0.0656); difference significant at day 43 (Sosne et al., Int J Mol Sci 2022)
SEER-2 (full-length thymosin β4 as RGN-259, not TB-500) NCT05555589	3	Recruiting (started April 2023)	70 adults with stage 2 or 3 neurotrophic keratopathy, planned	0.1% preservative-free RGN-259 ophthalmic solution five times daily for 28 days, versus vehicle	—
NL005 Phase IIb (recombinant full-length thymosin β4, not TB-500) NCT05984134	2	Completed (results not posted)	90 adults aged 18–75 with acute anterior STEMI treated with PCI; Beijing Northland Biotech, China	Intravenous NL005 0.5 µg/kg or 1.0 µg/kg or placebo, first dose within 12 hours after PCI, then daily on days 2–7	—
NL005 (recombinant full-length thymosin β4) in anterior STEMI NCT07586865	2	Not yet recruiting (posted May 2026)	189 adults with anterior ST-elevation myocardial infarction, planned; Beijing Northland	10 or 20 µg/kg intravenously once daily for 7 days	Primary endpoint is infarct size at day 90; no results posted. This is the full-length protein, not the TB-500 fragment.

Doses in other published studies

Published studies not listed in the trials table above: smaller or unregistered human studies first, then animal and cell studies. Doses are shown exactly as each study reported them. Animal studies report weight-based doses, absolute amounts or concentrations; none translates directly to people, and none is converted here.

Subjects	Design	Dose	Finding	Source
Humans: 9 patients with severe dry eye (the trial was designed for severe dry eye disease, including dry eye associated with graft-versus-host disease); full-length thymosin β4 as RGN-259, not TB-500	Small phase 2, multicentre (2 US sites), randomized, double-masked, placebo (vehicle)-controlled trial lasting 56 days (28 days' treatment plus 28 days' follow-up); registered NCT01393132, which is not in the article's trials list	RGN-259 (thymosin β4) 0.1% eye drops or vehicle, 6 times daily for 28 days	At day 56 the RGN-259 group (12 eyes) had a 35.1% reduction in ocular discomfort (P = 0.0141) and a 59.1% reduction in total corneal fluorescein staining (P = 0.0108) compared with vehicle (6 eyes), and the authors report the drops were safe and well tolerated in this small trial.	Sosne G et al., Cornea, 2015
Humans: 84 healthy Chinese volunteers (54 randomized to the single-dose part, 30 to the multiple-dose part); recombinant human thymosin β4 (NL005), not TB-500	First-in-human, single-centre, randomized, double-blind, placebo-controlled, dose-escalating phase I study with single- and multiple-dose parts (registration numbers CTR20170766 and CTR20181784 as listed in the paper)	Single intravenous dose of 0.05, 0.25, 0.5, 2.0, 5.0, 12.5 or 25.0 µg/kg, or placebo; multiple-dose cohorts received 0.5, 2.0 or 5.0 µg/kg intravenously once daily for 10 days; both parts were observed for 28 days	Adverse events were mild to moderate and equal in incidence and severity to placebo, with no dose-limiting toxicities or serious adverse events; plasma concentration, Cmax and AUC rose with dose without obvious accumulation, and the few anti-drug-antibody-positive samples became negative at follow-up.	Wang X et al., J Cell Mol Med, 2021
Humans: 40 healthy volunteers in 4 cohorts of 10; synthetic thymosin β4 (full-length), not TB-500	Randomized, placebo-controlled, single- and multiple-dose ascending study in healthy volunteers at a US clinical research unit (San Antonio, Texas)	Single intravenous dose of placebo or 42, 140, 420 or 1260 mg synthetic Tβ4; after safety review, the same dose given intravenously daily for 14 days	Adverse events were infrequent and mild or moderate, with no dose-limiting toxicities or serious adverse events; single-dose pharmacokinetics were dose-proportional, with half-life increasing as dose increased.	Ruff D et al., Ann N Y Acad Sci, 2010
Humans: 73 patients with venous stasis ulcers at 8 European sites (5 in Italy, 3 in Poland); synthetic thymosin β4 (a copy of the 43-amino-acid peptide), not TB-500	Phase 2 double-blind, placebo-controlled, dose-escalation study. The 2007 protocol report (Guarnera G et al., Ann N Y Acad Sci 2007, PMID 17495250) describes three sequentially enrolled groups randomized 3:1 to Tβ4 or placebo, treated for 84 days with standard class 2 compression stockings and followed for 14 days	Topical Tβ4 at increasing doses across three groups, for 84 days. The 2010 abstract names only 0.03% (the dose with a possible healing signal); the other concentrations and how often it was applied are not given in either abstract	The safety profile of all doses was deemed acceptable and comparable to placebo; the authors suggest 0.03% may have the potential to accelerate healing and report complete healing within 3 months in about 25% of patients, especially those whose wounds were small to moderate in size or mild to moderate in severity.	Guarnera G et al., Ann N Y Acad Sci, 2010
Rats: 32 male Sprague-Dawley rats (12 weeks old, about 330 g) after Achilles tendon transection and repair; 8 per group, with 4 tendons per group for biomechanics and 4 for histology	Randomized (simple randomization) controlled animal study with four groups (vehicle, BPC-157, TB-500, BPC-157 + TB-500) and biomechanical and histological outcomes at 30 days; blinding was not feasible during surgery or daily dosing. The TB-500 was a commercially purchased product identified by catalogue number; the paper describes it only as a synthetic peptide derived from Tβ4 and does not state its sequence (17–23 fragment or full-length)	TB-500 60 µg/kg/day intraperitoneally, once daily beginning on the first postoperative day, for 30 days. The combination group received BPC-157 10 µg/kg/day plus TB-500 60 µg/kg/day by the same route and schedule	The TB-500 group had higher maximum load to failure than controls (adjusted p = 0.0406) and lower total Bonar (p = 0.016) and Movin (p = 0.017) histology scores; the combination did not confer additional benefit over either agent alone.	Biçer O et al., Joint Diseases and Related Surgery, 2026
Horses: 2 Thoroughbred geldings	Doping-control analytical method study (LC-MS detection of seven peptides in horse plasma); TB-500 was given to two horses to show the method worked on real post-administration samples	Single subcutaneous administration of TB-500 containing 10 mg N-acetylated LKKTETQ	N-acetylated LKKTETQ and its metabolite N-acetylated LK were detected in plasma after administration; the study measured detection only, not efficacy or safety.	Kwok WH et al., Analytical and Bioanalytical Chemistry, 2013

Mixing examples reported by protocol websites

Examples for the freeze-dried powder, as reported by protocol websites, not taken from studies. The water amount only sets the concentration (how much is in each mL); it does not change how much of the compound is in the vial. Each concentration assumes the vial really holds its labelled amount and the final liquid volume equals the water added.

Vial	Water added	Concentration
10 mg	2.0 mL	5.0 mg/mL
10 mg	3.0 mL	3.33 mg/mL

Clean the rubber tops of both vials with an alcohol swab.
Add the water slowly, letting it run down the inside wall of the vial rather than onto the powder.
Swirl or roll gently until the powder dissolves; protocol sites advise against shaking.
The liquid should be clear. If it is cloudy or has specks in it, do not use it. Clear liquid does not show that the product is pure, the right strength or sterile.
Write the date and the concentration on the vial, and keep it in the fridge (2–8 °C). No safe storage time after mixing has been established for these products.

Products sold as "research peptides" have not gone through FDA review for safety, effectiveness or quality. Bacteriostatic water does not sterilize a contaminated powder. It contains benzyl alcohol, and its label says it is not for use in newborns. To work out a volume from your own numbers, use the converter.

Doses described in clinical or compounding practice

From FDA labels and documents, other regulators, published reviews and professional references, as each source states them. Unless a source says otherwise, these describe practice or proposals, not results tested in trials. Reading doses safely: how concentration and syringe markings work.

FDA's 2026 PCAC briefing says the withdrawn nomination (Wells Pharmacy Network) proposed "a 3 mg/mL lyophilized powder for SC and IM injection". FDA evaluated it for wound healing, based on the nomination's stated use. The nomination form reproduced in the briefing gives a strength ("3mg/mL") and route but no dose, frequency or duration. FDA says it found no articles in which TB-500 was given to humans, and no clinical studies or human exposure data by any route. (FDA Briefing Document: TB-500-Related Bulk Drug Substances, Pharmacy Compounding Advisory Committee, July 23-24, 2026, FDA document)
FDA's 2026 PCAC briefing on BPC-157 summarizes a FAERS report. A 40-year-old woman used a "BPC-157 and TB-500 (5mg/5mg) injection product" labelled for "research purposes only", injecting it "SC twice daily" for "joint healing and wound healing support". No amount per injection is stated. She developed diffuse hyperpigmentation and gingival darkening, and the same reactions came back when she used it again. FDA judged the reactions likely due to the product because they recurred on rechallenge. It adds that because the product contained two peptides, it is not possible to assess a relationship between BPC-157 and the reactions. (FDA Briefing Document: BPC-157-Related Bulk Drug Substances, PCAC, July 23-24, 2026 (FAERS report 26053573), FDA document)
This retrospective chart review of one Orlando clinic (2019-2020) found 4 patients who received intra-articular knee injections of BPC-157 plus compounded "thymosin-beta-4 (TB4)", with the two peptides injected separately into the joint. The paper says doses "varied from a low dose of BPC157 of 2 mg" with 3 mg of TB4 "to a high dose of BPC 157 of 4 mg" with 6 mg of TB4. Its Table 2 also lists one patient on 3 mg BPC-157 with 4.5 mg TB4. The paper describes TB4 as the natural thymus peptide and never calls it TB-500 or states the sequence of the compounded product, so this may be full-length thymosin β4 rather than the TB-500 fragment. The paper calls the work an "experimental trial using peptides", and it had no control group. (Lee E, Padgett B. Intra-Articular Injection of BPC 157 for Multiple Types of Knee Pain. Altern Ther Health Med 2021;27(4):8-13, Peer-reviewed)

Doses reported in online communities (untested)

Unverified, and not a recommendation. These are amounts people describe in online forums such as Reddit, collected so researchers can see how practice differs from the evidence. These forum accounts are not clinical evidence, even where they overlap studied doses. Products sold online as "research peptides" are not FDA approved, and their identity, purity and strength are not verified; they can be mislabeled, contaminated or wrongly dosed.

What people report

In the threads reviewed, people describe injecting products sold as TB-500 under the skin, mostly alongside BPC-157. Amounts fall into two broad patterns: about 250–1,000 mcg a day, or about 0.5–3 mg per injection given every other day to once a week. Commenters disagree on whether vials hold the 7-amino-acid fragment or full-length thymosin β4. Reported problems included migraine, fatigue, flu-like symptoms, sore muscles and diarrhoea; night-time heart palpitations; and worsening joint pain. Most reports involve combinations and untested products, so none can be attributed to TB-500 itself.

How this compares with the studies

Published human studies used full-length thymosin β4, not TB-500, given intravenously or topically; material sold as TB-500 has been dosed only in rats and horses. The molecules, routes and species differ and product contents are unverified, so study figures cannot be compared with thread amounts. No one in the threads reviewed cited a study for the long half-life claims used to justify weekly schedules.

Open questions a study would need to answer

With no published human pharmacokinetic data found for N-acetylated LKKTETQ, does it reach measurable levels in human blood after subcutaneous injection, and for how long?
What do products sold as TB-500 actually contain (the 17–23 fragment, full-length thymosin β4, or neither), and at what purity and endotoxin levels?
Are the palpitations, flu-like symptoms and joint pain described in the threads linked to TB-500, to the compounds injected with it, or to contamination?

Threads consulted, checked 2026-09-26: Dosing for TB500 (not TB4) (r/Peptides) · BPC-157 + TB500 for chronic shoulder pain - 30 days tracked data (r/Peptides) · TB500/BPC157 DOSE AND TIMING (r/Peptides) · Opposite Effects of BPC/TB (r/Peptides) · Heart thumping/palpitations from bpc157/tb500 (r/Peptides) · tb-4 vs tb500 (r/Peptides) · TB500 - interesting sides (r/moreplatesmoredates) · BPC 157 and TB500 Dosing (r/moreplatesmoredates)

Enforcement history

2023-09-29 · 503A Category 2 placement: FDA placed thymosin beta-4 fragment (LKKTETQ), also known as TB-500, in Category 2 of the interim 503A bulk drug substances policy, stating it had not identified any human exposure data and citing immunogenicity risk from aggregation and impurities. (source)
2026-04 · Withdrawn from Category 2: FDA's safety-risk page (updated 2026-04-22) now lists the thymosin beta-4 fragment under substances previously in Category 2 that were withdrawn by their nominators. It is not on the 503A bulks list. (source)
2026-07-23 · PCAC advisory vote: The Pharmacy Compounding Advisory Committee discussed TB-500 (free base and acetate) for the 503A bulks list, proposed use wound healing, and voted narrowly in favour. The vote is non-binding and FDA had not issued a final decision as of this article. (source)
2026-10-30 · HHS draft enforcement-discretion policy: HHS published a draft interim policy (docket HHS-OASH-2026-0496) saying it does not intend to take enforcement action against state-licensed pharmacies, federal facilities or licensed physicians that compound single-ingredient TB-500 products under section 503A while FDA rulemaking on the bulks list proceeds, provided conditions are met (bulk substance from an FDA-registered manufacturer with a certificate of analysis, patient-specific prescriptions, adverse-event reporting). The notice states the policy is not binding and does not add TB-500 to the 503A bulks list; comments are due two weeks after publication, about 2026-11-13. (source)

Side effects and warnings

Not catalogued yet.

Full lists are in the Scientific view.

Reported side effects

Not catalogued yet.

Interactions

Not catalogued yet.

Contraindications

Not catalogued yet.

Storage

No approved product exists, so there is no label storage data. Research suppliers generally state that the lyophilized powder is stored frozen or refrigerated and that solutions are refrigerated and used within days to weeks. Those are supplier claims, not verified data.

General storage guidance commonly given for freeze-dried research peptides and powders, not stability data for this substance. Storage conditions and usable life depend on the specific product and formulation; follow its documented instructions.

Condition	Temperature
Temporary (transportation), in powdered form	15 °C – 25 °C / 59 °F – 77 °F
Short term (1–3 years)	2 °C – 8 °C / 36 °F – 46 °F
After reconstitution (28 days)	2 °C – 8 °C / 36 °F – 46 °F
Long term (2–5 years)	−20 °C / −4 °F or below

Product characteristics

Form: Synthetic lyophilized peptide powder (research grade)

Appearance: White to off-white lyophilized powder

Solubility: Water-soluble

Compound information

Synthetic N-acetylated heptapeptide, free base or acetate salt. Vendors sometimes label full-length 43-residue thymosin β4 as "TB-500"; the two are different molecules with different molecular weights (889 vs 4,963 g/mol). No safety data sheet from a regulated drug manufacturer was found.

Molecule, patents, enforcement history, full trial tables and compound details are in the Scientific view.

Common questions

What is TB-500 (thymosin β4 fragment)?

Is TB-500 (thymosin β4 fragment) FDA approved?

Not FDA approved for any use.

What have studies found?

No human study has tested TB-500 itself. In trials of the full protein (thymosin β4), eye drops did no better than placebo for dry eye.
In one very small eye trial, 6 of 10 healed on the drops versus 1 of 8 on placebo. In safety studies of the full protein, side effects were about the same as with placebo.

How was it dosed in studies?

Is it legal to buy as a "research peptide"?

Products sold as "research use only" or "not for human consumption" are not approved for use in people. That label does not make them legal to sell for human use, and their contents are not checked by any regulator.

References

This page summarises the published sources below. PeptideBasics101 does no original research. Trial doses and results are reported as the cited study or label reported them. Sources can themselves be wrong or superseded; if you find a statement here that does not match its source, please tell us through our corrections process. Sources were last checked on 2026-11-01.

Based on 9 published references

FDA: certain bulk drug substances for use in compounding that may present significant safety risks (Category 2 and withdrawn substances) (fda.gov)
FDA: July 23–24, 2026 meeting of the Pharmacy Compounding Advisory Committee (fda.gov)
Low TL, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin beta 4. PNAS 1981 (pubmed.ncbi.nlm.nih.gov)
Goldstein AL, Hannappel E, Kleinman HK. Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues. Trends Mol Med 2005 (pubmed.ncbi.nlm.nih.gov)
Sosne G et al. 0.1% RGN-259 (thymosin β4) ophthalmic solution in neurotrophic keratopathy, Phase III (SEER-1). Int J Mol Sci 2022 (pmc.ncbi.nlm.nih.gov)
ClinicalTrials.gov: NCT02974907, ARISE-2 (RGN-259 in dry eye) (clinicaltrials.gov)
ClinicalTrials.gov: NCT07487363, TB-500 record whose summary describes it as a fictional example study (clinicaltrials.gov)
PubChem: TB-500 (CID 62707662) (pubchem.ncbi.nlm.nih.gov)
HHS: Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances, notice of availability (Federal Register, 2026-10-30) (govinfo.gov)

Clinical trial entries in the table above link to their ClinicalTrials.gov registry records. Spotted an error? See corrections.