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

> TB-500 and thymosin beta-4: how they differ, FDA and compounding status in 2026, WADA status, and what animal and human studies tested.

- Canonical URL: https://livingpluspeptides.com/peptides/tb-500-thymosin-beta-4/
- Last updated: October 28, 2026
- Publisher: Living+

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].

## Regulatory status

- FDA approved: No
- 503A compounding: [HHS interim enforcement policy (may be compounded under its conditions while FDA writes the 503A bulks list rule; not FDA approval)](https://www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretion-policy-appendix-b.pdf). On 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.
- 503B bulks list: [Not nominated](https://www.fda.gov/media/94164/download). Neither TB-500 nor thymosin beta-4 appears in any 503B category on FDA's 503B list updated March 21, 2025.
- WADA prohibited: [Yes](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf) (S2.3 Growth factors and growth factor modulators (thymosin-β4 and its derivatives, e.g. TB-500))
- FDA drug shortage: [Not on the shortage list](https://api.fda.gov/drug/shortages.json?search=generic_name:%22thymosin%22)
- DEA schedule: [Not scheduled](https://www.deadiversion.usdoj.gov/schedules/orangebook/c_cs_alpha.pdf)
- Last verified: October 28, 2026

Checked against: [HHS: Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances (Appendix A and B)](https://www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretion-policy-appendix-b.pdf), [Federal Register: HHS notice of availability, FR Doc. 2026-22192 (filed Oct 28, 2026; publishes Oct 30, 2026)](https://public-inspection.federalregister.gov/2026-22192.pdf), [FDA: Bulk drug substances nominated for use in compounding under section 503A (updated May 14, 2026)](https://www.fda.gov/media/94155/download), [FDA: Certain bulk drug substances for use in compounding that may present significant safety risks](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks), [FDA: Evaluation of TB-500-related bulk drug substances, PCAC briefing, July 2026](https://www.fda.gov/media/193349/download), [FDA: PCAC briefing document introduction, July 23-24, 2026](https://www.fda.gov/media/193342/download), [FDA: Bulk drug substances nominated for use in compounding under section 503B (updated March 21, 2025)](https://www.fda.gov/media/94164/download), [WADA: 2026 Prohibited List](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf), [openFDA Drugs@FDA query: thymosin (no matches)](https://api.fda.gov/drug/drugsfda.json?search=products.active_ingredients.name:%22thymosin%22), [openFDA drug shortages query: thymosin](https://api.fda.gov/drug/shortages.json?search=generic_name:%22thymosin%22), [DEA Diversion: Controlled Substances - Alphabetical Order](https://www.deadiversion.usdoj.gov/schedules/orangebook/c_cs_alpha.pdf)

## Key facts

- Class: TB-500: synthetic fragment of thymosin beta-4. Thymosin beta-4: natural actin-binding peptide [1, 7]
- Amino-acid 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 used 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

| Study | Year | Participants | Design | Result | Link |
| --- | --- | --- | --- | --- | --- |
| Human trial: RGN-259 eye drops for neurotrophic keratopathy (Sosne et al.) | 2022 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/36613994/) |
| Human trial: RGN-259 eye drops for dry eye (Sosne and Ousler) | 2015 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/26056426/) |
| Human trial: IV thymosin beta-4 phase 1 (Ruff et al.) | 2010 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/20536472/) |
| Human trial: Topical thymosin beta-4 for venous ulcers (Guarnera et al.) | 2010 | 73 adults with venous leg ulcers | Phase 2, double-blind, placebo-controlled, dose escalation, 8 European sites | Was studied for venous ulcers. Safety was similar to placebo. Authors suggested a 0.03% dose may speed wound closure [12]. | [Source](https://pubmed.ncbi.nlm.nih.gov/20536470/) |
| Animal study: TB-500 detection in horses (Ho et al.) | 2012 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/23084823/) |
| Animal study: Heart repair in mice (Bock-Marquette et al.) | 2004 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/15565145/) |
| Animal study: Skin wounds in diabetic and aged mice (Philp et al.) | 2003 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/12581423/) |
| Lab study: TB-500 metabolism and fibroblast scratch test (Rahaman et al.) | 2024 | 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]. | [Source](https://pubmed.ncbi.nlm.nih.gov/38382158/) |

## 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.

## Legal and regulatory status

- 2026-10-28: HHS issued an interim enforcement policy for certain peptides used in 503A compounding. Until a final rule decides whether TB-500 goes on the 503A bulks list, HHS does not intend to take action against state-licensed pharmacies, federal facilities or licensed physicians who compound it under the policy's conditions [19]. For TB-500 acetate, the policy covers subcutaneous or intramuscular injectable forms [19]. Conditions include a single active ingredient, bulk substance from an FDA-registered facility with a certificate of analysis, reporting of serious adverse events to FDA and a patient-specific prescription [19]. The policy is not FDA approval and does not place TB-500 on the 503A bulks list [19]. HHS may revisit it if a safety signal or product quality issue arises [19]. A Federal Register notice of availability, which calls the policy a draft, publishes October 30, 2026 [20]. [Source](https://www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretion-policy-appendix-b.pdf)
- 2026-07-23: FDA's Pharmacy Compounding Advisory Committee discussed TB-500 for the 503A bulks list, with wound repair as the use reviewed. FDA staff proposed that TB-500 and TB-500 acetate NOT be added. FDA's final decision comes after the committee process [4, 5]. HHS's October 28, 2026 policy states the committee voted in favor of both forms [19]. [Source](https://www.fda.gov/media/193342/download)
- 2026-05-14: FDA's 503A categories list, updated May 14, 2026, does not place TB-500 in category 1, 2 or 3. FDA lists it with substances previously in category 2 whose nominations were withdrawn [3, 2]. [Source](https://www.fda.gov/media/94155/download)
- 2026-04-16: A Federal Register notice (91 FR 20465) announced the July 2026 advisory committee meeting covering TB-500 [15]. [Source](https://www.govinfo.gov/content/pkg/FR-2026-04-16/pdf/2026-07361.pdf)
- 2026-01-01: The WADA 2026 Prohibited List took effect. It lists thymosin beta-4 and its derivatives, such as TB-500, under S2.3 growth factors, banned at all times [6]. [Source](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf)

See every peptide's status side by side in the [Peptide Status Tracker](https://livingpluspeptides.com/regulation/tracker/#row-tb-500-thymosin-beta-4).

## Frequently asked 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](https://www.fda.gov/media/193349/download)
2. [FDA: Certain bulk drug substances for use in compounding that may present significant safety risks](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
3. [FDA: Bulk drug substances nominated for use in compounding under section 503A (updated May 14, 2026)](https://www.fda.gov/media/94155/download)
4. [FDA: July 23-24, 2026 meeting of the Pharmacy Compounding Advisory Committee](https://www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-compounding-advisory-committee-07232026)
5. [FDA: PCAC briefing document introduction, July 23-24, 2026](https://www.fda.gov/media/193342/download)
6. [WADA: 2026 Prohibited List](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf)
7. [Low et al. 1981, PNAS (PubMed)](https://pubmed.ncbi.nlm.nih.gov/6940133/)
8. [Ho et al. 2012, J Chromatogr A (PubMed)](https://pubmed.ncbi.nlm.nih.gov/23084823/)
9. [Philp et al. 2003, Wound Repair Regen (PubMed)](https://pubmed.ncbi.nlm.nih.gov/12581423/)
10. [Ruff et al. 2010, Ann N Y Acad Sci (PubMed)](https://pubmed.ncbi.nlm.nih.gov/20536472/)
11. [Sosne and Ousler 2015, Clin Ophthalmol (PubMed)](https://pubmed.ncbi.nlm.nih.gov/26056426/)
12. [Guarnera et al. 2010, Ann N Y Acad Sci (PubMed)](https://pubmed.ncbi.nlm.nih.gov/20536470/)
13. [Sosne et al. 2022, Int J Mol Sci (PubMed)](https://pubmed.ncbi.nlm.nih.gov/36613994/)
14. [Bock-Marquette et al. 2004, Nature (PubMed)](https://pubmed.ncbi.nlm.nih.gov/15565145/)
15. [Federal Register: PCAC notice of meeting, April 16, 2026 (91 FR 20465)](https://www.govinfo.gov/content/pkg/FR-2026-04-16/pdf/2026-07361.pdf)
16. [FDA: Bulk drug substances nominated for use in compounding under section 503B (updated March 21, 2025)](https://www.fda.gov/media/94164/download)
17. [Treadwell et al. 2012, Ann N Y Acad Sci, review (PubMed)](https://pubmed.ncbi.nlm.nih.gov/23050815/)
18. [Rahaman et al. 2024, J Chromatogr B (PubMed)](https://pubmed.ncbi.nlm.nih.gov/38382158/)
19. [HHS: Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances (Oct 28, 2026)](https://www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretion-policy-appendix-b.pdf)
20. [Federal Register: HHS notice of availability, FR Doc. 2026-22192 (publishes Oct 30, 2026)](https://public-inspection.federalregister.gov/2026-22192.pdf)

Educational information, not medical advice. This site sells nothing.