The 30-second answer: TB-500 is not thymosin beta-4. It's a 7-amino-acid fragment copied from that 43-amino-acid protein. Most studies people cite for TB-500 used the full protein. In 2026, FDA found no human data on TB-500 itself. It is not an approved drug.
Search "TB-500 research" and you'll find rat wound studies, a heart paper in Nature and human eye-drop trials. Here's the twist: almost none of them used TB-500. They used its much bigger parent protein.
This guide sorts out which evidence belongs to which molecule. It covers laboratory, animal and clinical research only. It is not guidance on using anything.
In this article you'll learn:
- How TB-500 differs from thymosin beta-4, with a Lego analogy that makes it stick
- What the animal and human studies found, and which molecule each one used
- What the 2026 FDA vote and the new HHS policy do and don't mean
What is thymosin beta-4?
Thymosin beta-4 (Tβ4) is a 43-amino-acid protein found in nearly every human cell. Its job involves actin, the protein that forms each cell's internal scaffolding.
Think of actin as a pile of building blocks. A cell snaps them together to change shape and crawl. Tβ4 is the main protein in mammal cells that holds spare actin blocks in reserve. By holding them, it controls how fast a cell can rebuild its scaffold and move. [1]
That's why researchers got interested. Cell movement matters in wound closure, the eye's surface and the heart.
So what is TB-500?
Picture Tβ4 as a Lego castle with 43 bricks. A short stretch of six bricks, LKKTET, is the part that grips actin. TB-500 is a synthetic copy of just that stretch, positions 17 to 23, plus a small chemical cap called an acetyl group on the front. [3]
So TB-500 is the castle's front door, sold under the castle's name. Its sequence is written Ac-LKKTETQ. It weighs 889.01 g/mol. Full Tβ4 is about 4.9 kDa, so TB-500 is roughly one-fifth the size. [1]
"TB-500" is a market name, not a scientific one. A 2012 doping-control lab tested a product sold as TB-500. It found the capped 17–23 fragment, not the full protein. [3] Some sellers still use the name for full-length Tβ4.
Did you know? The human trials people cite for "TB-500" used a molecule more than five times heavier. In July 2026, FDA said it "did not find any information where TB-500 was administered to patients." [1]
What did the animal studies find?
Most animal work used full-length Tβ4. Here are the landmark results. Full details are in "The evidence in detail" below.
- Rat skin wounds (1999): Tβ4 sped up regrowth of the skin's top layer. It beat saline by 42% at day 4 and by up to 61% at day 7. Wounds also closed in more, with more collagen and new blood vessels. [4]
- Mice with slow repair (2003): in diabetic mice and in 26-month-old mice, Tβ4 increased wound contraction and collagen. [5]
- Mouse hearts (2004): after researchers tied off a heart artery, Tβ4 improved early heart-muscle cell survival and heart function. [6]
One fragment result stands out. The 2003 study also tested a 7-amino-acid peptide, LKKTETQ. In aged mice, it promoted repair "comparable to that observed with the parent molecule." But that peptide had no acetyl cap. TB-500 has one. So this is a close cousin of TB-500, not a direct test of it.
Has anyone studied TB-500 itself?
Barely. A 2024 rat study tracked what happens to TB-500 as the body breaks it into smaller pieces, called metabolites. [7]
- The main breakdown piece, Ac-LK, peaked in the first 6 hours.
- Another piece, Ac-LKK, was still detectable at 72 hours.
- None of the compounds harmed cells in culture.
- In a dish test of wound closure, only one piece, Ac-LKKTE, showed significant activity. TB-500 itself did not.
The authors concluded that activity credited to TB-500 tracks to that breakdown piece, not the parent.
FDA's 2026 review came at it from the other side. It said it "did not identify" any published animal studies of TB-500 on wounds. [1]
Did you know? In a 2024 study, TB-500 did nothing measurable in a dish wound-closure test. One of its breakdown fragments did. [7]
What this means for you: If you design a TB-500 study, you're working near the edge of the evidence. The strong animal data belongs to the full protein. The fragment has chemistry, one metabolism study and little else.
What did the human trials find?
Every controlled human study used full-length Tβ4, including an eye-drop version called RGN-259. None used TB-500. [11]
Here's the short version:
- Safety studies (IV, healthy adults): two phase 1 trials found mild or moderate side effects and no serious ones. A phase 1 trial is the first, small safety step in people. [8] [12]
- Venous skin ulcers (gel, 73 patients): safety looked like placebo. The authors called the efficacy findings preliminary. [9]
- Dry eye (72 adults): the trial missed both of its main goals. Some secondary measures improved. [10]
- An eye-surface disorder called neurotrophic keratopathy (18 patients): at 4 weeks, 6 of 10 on Tβ4 had full surface closure, vs 1 of 8 on placebo. With so few patients, that gap wasn't statistically significant. [11]
"Statistically significant" means the gap is big enough that chance is an unlikely explanation. With 18 people, even a big-looking gap can fall short.
What this means for you: Full Tβ4 has a modest human safety record and small, mixed signals of benefit. TB-500 has no human record at all. In FDA's words, the nomination "did not include, and FDA has not identified, any clinical studies or human exposure data for TB-500 via any ROA." (ROA means route of administration.)
Compare: BPC-157 research overview · BPC-157 vs. TB-500 compared
What's the legal status in 2026? (checked October 29, 2026)
The short version: TB-500 is not an FDA-approved drug. Neither is Tβ4. Here's how 2026 unfolded.
- April 15: FDA removed TB-500 and other peptides from 503A "Category 2" ahead of committee review. (503A is the part of federal law that covers pharmacies mixing drugs for one patient's prescription.) That did not authorize compounding.
- July: FDA staff recommended against adding TB-500 to the 503A bulks list. They cited no human data, no animal wound studies, no toxicity studies, immune-reaction risk for injected peptides, and thin quality data. [1]
- July 23: the Pharmacy Compounding Advisory Committee (PCAC), FDA's outside advisers, voted 8–6 to recommend TB-500 anyway. BPC-157 and KPV got the same 8–6 result; MOTS-c got 7–5. [2]
- October 28: HHS issued an interim enforcement-discretion policy. It covers 503A compounding of BPC-157, TB-500, KPV, MOTS-c, epitalon and semax, for named forms and routes, by prescription only. It excludes 503B outsourcing facilities. [14]
"Enforcement discretion" means HHS says it won't act against licensed pharmacies and physicians compounding these peptides while rulemaking continues. HHS dates the end of Category 2 status to April 22, 2026. HHS says it can revisit the policy if a safety or quality problem appears. [14]
It is not FDA approval. It does not cover research-use-only products. And WADA, the World Anti-Doping Agency, prohibits "thymosin-β4 and its derivatives e.g. TB-500" at all times. [13]
Did you know? FDA's own staff recommended against TB-500. Its advisory committee then voted 8–6 for it. [1]
Full timeline: The FDA's July 2026 peptide vote, explained
Myth vs fact
| Myth | Fact |
|---|---|
| "TB-500 is thymosin beta-4." | It's a 7-amino-acid fragment of the 43-amino-acid protein. |
| "TB-500 has human trials." | FDA found none as of July 2026. The human trials used full Tβ4. |
| "The 2026 vote or HHS policy means FDA approved it." | Neither is approval. Both concern prescription pharmacy compounding only. |
| "The HHS policy covers research peptides." | It does not cover research-use-only products. |
| "It's fine in sport." | WADA prohibits it at all times. |
What should a TB-500 certificate of analysis show?
FDA's reviewers criticized the nomination's certificates of analysis (COAs). They lacked impurity limits, aggregation data, bioburden (bacterial count) and endotoxin results. That critique doubles as a checklist for research material:
- [ ] Mass identity. Mass spectrometry weighs the molecule. Expect a main peak near 889 Da (free base). A peak near 4.9 kDa means full-length Tβ4, not TB-500.
- [ ] Sequence stated: Ac-LKKTETQ, with the acetyl cap. Without it, you have plain LKKTETQ, the 2003 mouse-study peptide.
- [ ] HPLC purity per lot, with the chromatogram.
- [ ] Impurity profile: short or missing-brick versions left over from synthesis.
- [ ] Endotoxin (LAL) result for any cell or animal work.
- [ ] Lot match between vial and COA, plus a named third-party lab.
ProGrade publishes a lot-matched COA for research-grade TB-500.
Read next: how to read a COA · Wolverine stack: BPC-157 + TB-500 · best peptides for recovery research
The evidence in detail
For readers who want the specifics.
The two molecules
| Thymosin beta-4 (Tβ4) | TB-500 | |
|---|---|---|
| What it is | Naturally occurring protein | Synthetic fragment of Tβ4 (residues 17–23) |
| Length and sequence | 43 amino acids | 7 amino acids: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH (Ac-LKKTETQ) |
| Molecular weight | ~4.9 kDa | 889.01 g/mol (free base); 949.1 g/mol (acetate salt) |
| Human trial data | Phase 1–3 trials of eye drops, topical gel and IV infusion | None identified by FDA as of July 2026 |
| Main research focus | Cell migration, wound closure, cornea, heart | Doping-control detection, metabolism, a handful of in vitro studies |
Animal studies
Malinda et al., 1999 (USUHS and George Washington University). Rat full-thickness wound model. Topical or intraperitoneal Tβ4 increased re-epithelialization by 42% over saline at day 4 and by up to 61% at day 7. Wounds contracted at least 11% more by day 7, with more collagen deposition and new blood vessels. In cell assays, as little as 10 pg of Tβ4 raised keratinocyte migration 2–3-fold. [4]
Philp et al., 2003. In diabetic (db/db) mice, Tβ4 increased wound contraction and collagen deposition. In 26-month-old mice, it increased keratinocyte migration, contraction and collagen. The unacetylated LKKTETQ peptide promoted repair in aged mice "comparable to that observed with the parent molecule." [5]
**Bock-Marquette et al., 2004 (UT Southwestern, Nature).** Tβ4 forms a complex with PINCH and integrin-linked kinase (ILK), activating the survival kinase Akt. After coronary artery ligation in mice, Tβ4 raised ILK and Akt activity, improved early cardiomyocyte survival and improved cardiac function. [6]
Rahaman et al., 2024. Assay for TB-500 and its metabolites in rats. Main metabolite Ac-LK, highest in the first 6 hours. Ac-LKK detectable up to 72 hours. No cytotoxicity. Only Ac-LKKTE was active in an in vitro wound-closure assay. FDA's 2026 briefing: "the nominator did not submit, and FDA did not identify, published nonclinical in-vivo studies assessing the potential effects of TB-500 on wounds." [7] [1]
Human trials (all full-length Tβ4)
| Study | Design | Participants | Reported result |
|---|---|---|---|
| IV Tβ4, phase 1 (Ruff et al., 2010) | Randomized, placebo-controlled; single and 14-day multiple ascending doses | 4 cohorts of 10 healthy adults | Adverse events infrequent, mild or moderate; no dose-limiting toxicities or serious adverse events |
| Topical Tβ4, venous ulcers, phase 2 (Guarnera et al., 2010) | Double-blind, placebo-controlled, dose escalation, 8 European sites | 73 patients | Safety comparable to placebo; efficacy described by the authors as preliminary, with complete wound closure within 3 months in about 25% of patients |
| RGN-259 eye drops, dry eye, phase 2 (Sosne & Ousler, 2015) | Double-masked, placebo-controlled, 28 days, controlled adverse environment model | 72 adults | Neither primary endpoint met. Secondary: 27% lower discomfort in the environment chamber at day 28 (P=0.0244); better central and superior corneal staining; no adverse events observed |
| RGN-259 eye drops, neurotrophic keratopathy, phase 3 (Sosne et al., 2022) | Double-masked, placebo-controlled | 18 (10 Tβ4, 8 placebo) | Complete epithelial closure at 4 weeks: 6 of 10 vs 1 of 8 (P=0.0656, not significant). Significant difference at day 43 (P=0.0359) |
| Recombinant Tβ4 (NL005), IV, phase 1 (Wang et al., 2021) | Randomized, double-blind; single and 10-day multiple ascending doses | 54 single-dose + 30 multiple-dose healthy adults | Adverse events mild to moderate; no dose-limiting toxicities or serious adverse events; no obvious accumulation |
Sources: [8] · [9] · [10] · [11] · [12]
Regulatory detail
| Item | Status (checked Oct 29, 2026) |
|---|---|
| FDA staff recommendation (July 2026) | "FDA is proposing that TB-500 (free base) and TB-500 acetate NOT be included on the 503A Bulks List." Reasons: no human data, no in vivo wound studies, no toxicity studies, immunogenicity risk for injected peptides, nomination COAs lacking impurity, aggregation and endotoxin data |
| PCAC vote (July 23, 2026) | 8–6 to recommend TB-500 (free base and acetate) for the 503A bulks list, for the nominated use of wounds. Epitalon and semax were also recommended at the Jul 23–24 meeting |
| HHS policy (Oct 28, 2026) | Interim enforcement discretion for 503A compounding of six named peptides; named forms and routes; prescription only; excludes 503B; rulemaking continues. Filed Oct 28, published in the Federal Register Oct 30, 2026 |
| WADA Prohibited List | Prohibited at all times under S2: "Thymosin-β4 and its derivatives e.g. TB-500" |
For research use only. Not for human consumption. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Products are sold for research purposes only. This article summarizes published laboratory, animal and clinical research and is not medical advice.
References
- FDA. July 23–24, 2026 Pharmacy Compounding Advisory Committee briefing document (TB-500 evaluation). www.fda.gov/media/193773/download
- FDA. July 23–24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24…
- Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. 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 potential. Drug Test Anal. 2012;4(9). pubmed.ncbi.nlm.nih.gov/22962027/
- Malinda KM, Sidhu GS, Mani H, et al. Thymosin β4 accelerates wound healing. J Invest Dermatol. 1999;113(3):364–368. doi.org/10.1046/j.1523-1747.1999.00708.x
- Philp D, Badamchian M, Scheremeta B, Nguyen M, Goldstein AL, Kleinman HK. Thymosin β4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair Regen. 2003;11(1):19–24. doi.org/10.1046/j.1524-475X.2003.11105.x
- Bock-Marquette I, Saxena A, White MD, DiMaio JM, Srivastava D. Thymosin β4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432:466–472. www.nature.com/articles/nature03000
- Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS. J Chromatogr B. 2024;1235:124033. pubmed.ncbi.nlm.nih.gov/38382158/
- Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin β4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223–229. pubmed.ncbi.nlm.nih.gov/20536472/
- Guarnera G, DeRosa A, Camerini R. The effect of thymosin treatment of venous ulcers. Ann N Y Acad Sci. 2010;1194:207–212. pubmed.ncbi.nlm.nih.gov/20536470/
- Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE) model. Clin Ophthalmol. 2015;9:877–884. pubmed.ncbi.nlm.nih.gov/26056426/
- Sosne G, Kleinman HK, Springs C, Gross RH, Sung J, Kang S. 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. Int J Mol Sci. 2022;24(1):554. pubmed.ncbi.nlm.nih.gov/36613994/
- Wang X, Liu L, Qi L, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17). pubmed.ncbi.nlm.nih.gov/34346165/
- World Anti-Doping Agency. The Prohibited List (S2: thymosin-β4 and its derivatives e.g. TB-500). www.wada-ama.org/en/prohibited-list
- HHS. Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances. Federal Register doc 2026-22192, Docket HHS-OASH-2026-0496; filed for public inspection Oct 28, 2026, published Oct 30, 2026. www.federalregister.gov/d/2026-22192. Policy text with appendices: www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretio…
Research use only
This article is provided for educational and informational purposes and summarizes published laboratory and preclinical research. All ProGrade Peptides products are sold strictly for in-vitro laboratory and research use only (RUO). Nothing here is medical advice, a therapeutic claim, or a protocol for human or animal use. These compounds are not intended to diagnose, treat, cure, or prevent any disease.
Frequently asked questions
No. Thymosin beta-4 is a 43-amino-acid protein of about 4.9 kDa. TB-500 is a 7-amino-acid synthetic fragment, Ac-LKKTETQ, of 889 Da. It copies the actin-binding region of Tβ4.
FDA found no published human studies or human exposure data for TB-500 as of its July 2026 review. The human trials people cite used full-length thymosin beta-4.
Phase 1 IV trials reported no dose-limiting toxicities. A phase 2 dry-eye trial missed both primary endpoints but improved some secondary measures. A small phase 3 trial in neurotrophic keratopathy showed 6 of 10 vs 1 of 8 complete closures at 4 weeks. That gap was not statistically significant.
No. On July 23, 2026, FDA's advisory committee voted 8–6 to recommend TB-500 for the 503A bulks list, against FDA staff's recommendation. On Oct 28, 2026, HHS issued an interim enforcement-discretion policy for prescription 503A compounding while rulemaking continues, which is not approval.
No. It covers prescription compounding by licensed 503A pharmacies and physicians, for named forms and routes, and excludes 503B facilities. It does not cover research-use-only products.
Yes. WADA lists "thymosin-β4 and its derivatives e.g. TB-500" as prohibited at all times under S2.
Drafted with AI assistance and fact-checked against the cited sources by The ProGrade Research Desk. See our editorial policy and sourcing policy. Spot an error? Report it.
