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Peptide profile

TB-500 and Thymosin Beta-4: FDA Status, Research and Uses

By Living+. Updated October 28, 2026.

Key takeaway

TB-500 is a lab-made 7 amino acid piece of thymosin beta-4, a natural 43 amino acid peptide. TB-500 is not FDA approved, and FDA found no human studies of it. Full-length thymosin beta-4 was tested in small human trials of eye drops, a topical skin treatment and IV doses. WADA bans both in sport [1, 7, 6].

At a glance

Where it stands

Checked

  • FDA approvedNoNo approved product
  • Pharmacy compounding (503A)HHS interim policyOn HHS's interim enforcement policy (Appendix A), released Oct 28, 2026. HHS does not intend to take action against a state-licensed pharmacy, federal facility or licensed physician compounding TB-500 acetate for subcutaneous or intramuscular injection, with a patient-specific prescription and the policy's other conditions (FDA-registered source with a certificate of analysis, single ingredient, adverse event reporting). It is not FDA approval and not a place on the 503A bulks list; HHS may revisit it if a safety or quality problem arises. The July 2026 advisory committee voted in favor of listing it, and FDA's final rule is still pending.
  • Outsourcing facilities (503B)Not nominatedNeither TB-500 nor thymosin beta-4 appears in any 503B category on FDA's 503B list updated March 21, 2025.
  • WADA (sport)ProhibitedS2.3 Growth factors and growth factor modulators (thymosin-β4 and its derivatives, e.g. TB-500)
Same data as the Status Tracker. Checked against 11 sources

Key facts

Class
TB-500: synthetic fragment of thymosin beta-4. Thymosin beta-4: natural actin-binding peptide [1, 7]
Length
TB-500: 7 amino acids (acetylated LKKTETQ). Thymosin beta-4: 43 amino acids [1, 7]
Half-life
Not established in humans for TB-500. For IV thymosin beta-4, half-life rose as the dose rose in a phase 1 study [1, 10]
Route in studies
TB-500: under the skin in horses and intraperitoneal in rats. Thymosin beta-4: eye drops, topical on skin ulcers and IV in human trials [1, 10, 11, 12]
First studied
Thymosin beta-4 sequenced in 1981. TB-500 first made from it around 2003 [7, 1]

How it works

Thymosin beta-4 is a 43 amino acid peptide first isolated from calf thymus and sequenced in 1981 [7]. It is found in many cell types and in body fluids such as blood, saliva, tears and wound fluid [1]. One of its known roles is to bind G-actin, a building block of the cell's internal skeleton. This helps control cell shape and movement [1].

TB-500 is not the same molecule. It is a synthetic 7 amino acid copy of amino acids 17 to 23 of thymosin beta-4, with an acetyl group added at one end [1]. This short stretch, LKKTETQ, holds the actin-binding site [8]. FDA notes that adding the acetyl group can change how a peptide behaves, so results for the natural fragment cannot simply be applied to TB-500 [1].

In mice, both thymosin beta-4 and the unmodified LKKTETQ fragment were linked to faster skin wound repair [9]. Thymosin beta-4 was also linked to heart cell survival after induced heart attacks in mice [14]. In contrast, a 2024 lab study found TB-500 itself did not speed closure of scratched fibroblast cultures, while one of its breakdown products had a small effect [1, 18]. In horses and rats, TB-500 is broken down into shorter pieces that show up in blood and urine [1, 8].

What the research shows

4 human trials3 animal studies1 lab study

  1. 2022Human trial

    RGN-259 eye drops for neurotrophic keratopathy (Sosne et al.)

    18 adults with neurotrophic keratopathy Phase 3, randomized, double-masked, placebo-controlled

    Full closure of the corneal defect at 4 weeks in 6 of 10 on drops vs 1 of 8 on placebo. This difference was not statistically significant (p = 0.0656) [13].

    Read the study
  2. 2015Human trial

    RGN-259 eye drops for dry eye (Sosne and Ousler)

    72 adults with moderate to severe dry eye Phase 2, randomized, double-masked, placebo-controlled, 28 days

    0.1% thymosin beta-4 eye drops missed both primary endpoints. Some secondary measures improved, and no adverse events were seen [11].

    Read the study
  3. 2010Human trial

    IV thymosin beta-4 phase 1 (Ruff et al.)

    40 healthy adults (4 cohorts of 10) Randomized, placebo-controlled, single dose then 14 daily IV doses

    Full-length thymosin beta-4, not TB-500, was tested for safety. Adverse events were infrequent and mild or moderate, with no dose-limiting toxicity [10].

    Read the study
  4. 2010Human trial

    Topical thymosin beta-4 for venous ulcers (Guarnera et al.)

    Studied for venous ulcers

    73 adults with venous leg ulcers Phase 2, double-blind, placebo-controlled, dose escalation, 8 European sites

    Safety was similar to placebo. Authors suggested a 0.03% dose may speed wound closure [12].

    Read the study
  5. 2012Animal study

    TB-500 detection in horses (Ho et al.)

    Horses Doping-control method study after a single 10 mg dose of TB-500

    TB-500 and its breakdown products were found in horse plasma and urine [8].

    Read the study
  6. 2004Animal study

    Heart repair in mice (Bock-Marquette et al.)

    Mice and cultured heart cells Coronary artery tie model plus cell culture

    Thymosin beta-4 was linked to better early heart cell survival and heart function after injury [14].

    Read the study
  7. 2003Animal study

    Skin wounds in diabetic and aged mice (Philp et al.)

    Mice and rats Full-thickness skin wound models, topical thymosin beta-4 or LKKTETQ fragment

    Thymosin beta-4 and the unmodified 7 amino acid fragment were linked to faster wound repair in aged mice [9].

    Read the study
  8. 2024Lab study

    TB-500 metabolism and fibroblast scratch test (Rahaman et al.)

    Cell culture, human serum and rats Lab metabolism study plus fibroblast wound-closure assay

    TB-500 at 50 micrograms per mL did not speed scratch closure vs control. One metabolite caused a small closure [1, 18].

    Read the study

Doses used in studies

No human dose of TB-500 has been established, because FDA found no human studies or human exposure data for it by any route [1]. Animal doses include a single 10 mg dose under the skin in horses and 50 mg per kg into the abdomen in rats [1]. The lab study used 50 micrograms per mL in cell culture [1].

Full-length thymosin beta-4 is a different molecule with its own trial doses. A phase 1 study gave 42, 140, 420 or 1260 mg IV daily for 14 days to healthy adults [10]. Eye drop trials used a 0.1% solution [11, 13], and a venous ulcer trial suggested 0.03% as a topical dose [12].

Dosing is set by a licensed provider.

Side effects and safety

FDA says TB-500 may cause immune reactions, especially as an injection, because peptides can clump and may carry impurities [1, 2]. FDA found no clinical studies or human exposure data for TB-500, so its risks in people are unknown [1]. FDA also found no animal toxicity studies of TB-500 [1].

FDA's drug adverse event database (FAERS) had no reports for TB-500. FDA's food and supplement complaint system had two reports about blended TB-500 and BPC-157 products, but they had no safety assessments [1]. There is no FDA label or boxed warning because no TB-500 product is approved [1].

In trials of full-length thymosin beta-4, IV doses up to 1260 mg daily for 14 days had infrequent mild or moderate adverse events [10]. Topical and eye drop trials reported safety similar to placebo or no adverse events [11, 12, 13]. These results apply to thymosin beta-4 under trial conditions, not to TB-500.

Common questions

Is TB-500 the same as thymosin beta-4?

No. Thymosin beta-4 has 43 amino acids. TB-500 is a synthetic 7 amino acid fragment of it with an acetyl group added [1, 7].

Is TB-500 FDA approved?

No. FDA says TB-500 is not part of any FDA-approved drug and has no USP monograph [1].

Can a US pharmacy compound TB-500?

TB-500 is still not on the 503A bulks list and is not FDA approved, and FDA's final rule is pending [1, 3, 19]. FDA staff proposed against adding it in July 2026 [5]. Since October 28, 2026, an HHS interim policy says HHS does not intend to take action against state-licensed pharmacies, federal facilities or licensed physicians who compound TB-500 acetate under set conditions [19]. It covers subcutaneous or intramuscular injectable forms [19]. The policy is not FDA approval, and HHS may revisit it [19].

Has TB-500 been tested in humans?

FDA found no articles in which TB-500 was given to humans [1]. Human trials used full-length thymosin beta-4 instead [10, 11, 12, 13].

Is TB-500 banned in sports?

Yes. WADA's 2026 list names thymosin beta-4 and derivatives such as TB-500 under S2.3, banned in and out of competition [6].

What is TB-500 promoted for online?

FDA found sites promoting it for tendon, muscle and wound repair, endurance and more, with no human studies behind those uses [1].

Where did TB-500 come from?

FDA says it appears to have first been made from thymosin beta-4 in 2003. A veterinary version appeared in 2011 for horse and greyhound racing [1].

What are the side effects of TB-500?

They are unknown in humans. FDA found no clinical studies and is concerned about immune reactions to injected peptides [1, 2].

Sources

  1. FDA: Evaluation of TB-500-related bulk drug substances, PCAC briefing, July 2026
  2. FDA: Certain bulk drug substances for use in compounding that may present significant safety risks
  3. FDA: Bulk drug substances nominated for use in compounding under section 503A (updated May 14, 2026)
  4. FDA: July 23-24, 2026 meeting of the Pharmacy Compounding Advisory Committee
  5. FDA: PCAC briefing document introduction, July 23-24, 2026
  6. WADA: 2026 Prohibited List
  7. Low et al. 1981, PNAS (PubMed)
  8. Ho et al. 2012, J Chromatogr A (PubMed)
  9. Philp et al. 2003, Wound Repair Regen (PubMed)
  10. Ruff et al. 2010, Ann N Y Acad Sci (PubMed)
  11. Sosne and Ousler 2015, Clin Ophthalmol (PubMed)
  12. Guarnera et al. 2010, Ann N Y Acad Sci (PubMed)
  13. Sosne et al. 2022, Int J Mol Sci (PubMed)
  14. Bock-Marquette et al. 2004, Nature (PubMed)
  15. Federal Register: PCAC notice of meeting, April 16, 2026 (91 FR 20465)
  16. FDA: Bulk drug substances nominated for use in compounding under section 503B (updated March 21, 2025)
  17. Treadwell et al. 2012, Ann N Y Acad Sci, review (PubMed)
  18. Rahaman et al. 2024, J Chromatogr B (PubMed)
  19. HHS: Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances (Oct 28, 2026)
  20. Federal Register: HHS notice of availability, FR Doc. 2026-22192 (publishes Oct 30, 2026)

Updated October 28, 2026. Educational information, not medical advice.