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Research · Peptides and SARMs

TB-500

Grey marketNot approved for human use in the US, and sold anyway.

TB-500 is not FDA-approved and is banned in sport. Its claimed benefits for tendon repair, wound healing and inflammation rest on animal and lab studies. FDA found no clinical studies or human exposure data by any route, and stated its risks in humans are unknown. TB-500 is a seven amino acid fragment, distinct from full-length thymosin beta-4.

Add to Bio HackChecked 2026-11-13
Status
Not FDA-approved for any use in the US. FDA removed TB-500 from compounding category 2 on April 22, 2026, after its nomination was withdrawn, and did not place it in category 1. Under a draft, interim HHS policy announced October 30, 2026, HHS does not intend to take enforcement action against state-licensed pharmacies, federal facilities or licensed physicians compounding with TB-500 while the 503A bulks list is developed through rulemaking. Prohibited at all times by WADA (S2).
Also called
thymosin beta-4 fragment, TB4 fragment, LKKTETQ, TB-500 acetate, TB500
Taken for
injury recovery, tendon and muscle healing, wound healing, flexibility, inflammation

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help0

No benefit shown in research yet.

Reported risks8

What people take it for, and what was found

Claimed, not studied in people3

Untested

Tendon healing

Not studied in people. One rat study found stronger repaired Achilles tendons and better tissue scores after 4 weeks of TB-500.

No study in people. This rests on animal studies.

The numbers and sources
Effect
In rats whose Achilles tendon was cut and repaired, those given TB-500 for 4 weeks had a higher maximum load to failure than controls, a statistically significant difference, and lower total tendon damage scores on two microscopic scoring scales. Adding BPC-157 to TB-500 gave no further benefit over either alone [15]. A 2026 review found that direct musculoskeletal evidence for full-length thymosin beta-4 is limited to lab and rodent studies, and that TB-500 has no validated equivalence with it [9].
Population
32 male rats, 8 in each of four groups [15].
Sources
[15], [9]
Caveats
One small study, which its authors describe as exploratory and preliminary [15]. Surgically cut tendons in rats do not show what happens in people. FDA found no clinical studies of TB-500 by any route [3].
Untested

Wound healing

Not studied in people. In aged mice, the seven amino acid TB-500 sequence sped skin wound repair comparably to full-length thymosin beta-4.

No study in people. This rests on animal studies, lab studies.

The numbers and sources
Effect
In 26-month-old mice with full-thickness skin wounds, a synthetic peptide matching thymosin beta-4's seven amino acid actin-binding domain, LKKTETQ, promoted repair comparable to that seen with the full protein [16]. In the lab, the actin-binding motif matched thymosin beta-4's activity in human endothelial cell migration and in blood vessel sprouting from chick aortic tissue, while peptides lacking any part of it were inactive [17].
Population
Aged mice [16]. Human endothelial cells and chick aortic tissue in the lab [17].
Sources
[16], [17], [12], [9]
Caveats
These studies used the LKKTETQ sequence. An analysis of one TB-500 product identified an acetylated form, Ac-LKKTETQ [12]. Mouse skin wounds do not show what happens in people, and trials of full-length thymosin beta-4 do not describe TB-500 [9].
Untested

Inflammation

Not studied in people. In lab brain immune cells and in a mouse model of Alzheimer's disease, TB-500 lowered signs of inflammation.

No study in people. This rests on lab studies, animal studies.

The numbers and sources
Effect
In a microglia cell line, the brain's immune cells, TB-500 suppressed the nitric oxide production and pro-inflammatory cytokine expression set off by bacterial lipopolysaccharide. In 5xFAD mice, a model of Alzheimer's disease, it reduced glial activation in the brain [18].
Population
Cells in the lab, and 5xFAD mice [18].
Sources
[18]
Caveats
The study measured brain inflammation in a model of Alzheimer's disease, not the injury or joint inflammation TB-500 is taken for. It tested another thymosin beta-4 fragment, Ac-SDKP, alongside TB-500 [18].

Not yet researched2

No research yet

Muscle healing

We haven't sourced research on this yet.

No research yet

Flexibility

We haven't sourced research on this yet.

Risks

Reported risks8

LimitedHow often is not known

FDA compounding category 2 listing

FDA states compounded TB-500 may risk immune reactions and it has no human exposure data. FDA removed it from category 2 in April 2026.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
FDA states that compounded drugs containing thymosin beta-4 fragment (LKKTETQ), also known as TB-500, may pose a risk of immunogenicity for certain routes because of possible aggregation and peptide-related impurities. FDA identified no human exposure data and states it lacks information on whether the drug would cause harm in humans. TB-500 appears on FDA's list of substances previously in category 2 whose nominations were withdrawn by the nominators [1]. FDA removed TB-500 from category 2 on April 22, 2026, because the nomination was withdrawn, and TB-500 does not appear in category 1 of that update [2].
Population
Compounded drug products in the US [1][2].
Sources
[1], [2]
Caveats
A regulatory assessment of compounded products, not a study of harm.
LimitedHow often is not known

FDA's 2026 safety review

FDA states there are no human studies of TB-500 and its safety risks in humans are unknown, and weighed against allowing it for pharmacy compounding.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
FDA's briefing document for its Pharmacy Compounding Advisory Committee found no clinical studies or human exposure data for TB-500 by any route, and no human pharmacokinetic studies. It concluded that potential safety risks in humans are unknown. FDA described TB-500 as not well characterized, with tests for impurities, aggregates and microbial quality not publicly available, and identified no carcinogenicity studies. It stated that injected forms may pose a significant risk of immune reactions. FDA concluded that the balance of criteria weighs against placing TB-500 on the list of substances allowed for pharmacy compounding [3].
Population
FDA review of published literature, adverse event databases and the nomination [3].
Sources
[3]
Caveats
The advisory committee met on July 23, 2026, and its votes are advice to FDA, which makes the final determination [3]. Trade press reported that the committee voted 8 to 6, with 1 abstention, to recommend adding TB-500 to the 503A bulks list [4][5]. No FDA-published tally was located for this page.
LimitedHow often is not known

HHS interim compounding policy

HHS states it does not intend to take enforcement action against licensed compounding with TB-500 for now. Compounded drugs are not FDA-approved.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In a notice of a draft, interim policy, HHS states that it does not intend to take enforcement action against a State-licensed pharmacy, Federal facility or licensed physician compounding with a peptide listed in the policy's Appendix A while the 503A bulks list is developed through rulemaking [6]. TB-500 is on that list [7]. The notice states: "Compounded drugs are not FDA-approved, which means FDA does not review their safety, effectiveness, or quality before they are marketed." HHS may revisit the policy "if, among other things, a safety signal or product quality issue arises" with a compounded product it covers, and the policy is "not binding on HHS or the public" [6].
Population
Compounded drug products in the US [6][7].
Sources
[6], [7]
Caveats
A statement of enforcement intent, not an FDA approval and not a study of harm. FDA's future rulemaking may or may not add TB-500 to the 503A bulks list [6].
LimitedHow often is not known

Reported adverse events

Case reports: one report of skin and gum darkening with a product combining TB-500 and BPC-157. FDA found no other case reports.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
FDA's adverse event database held no reports for TB-500 through March 26, 2025, and FDA found no case reports in the published literature. FDA's food and supplement complaint system held two cases about blended TB-500 and BPC-157, without safety assessments [3]. A separate report described diffuse darkening of the skin and gums that recurred on re-exposure, with a product containing both BPC-157 and TB-500 labeled for research purposes only [8].
Population
Voluntary reports to FDA [3][8].
Sources
[3], [8]
Caveats
With two peptides in one product, the cause cannot be assigned to either [8]. Reporting is voluntary and incomplete [3].
LimitedHow often is not known

Not the same as thymosin beta-4

Limited evidence: TB-500 is a separate fragment of thymosin beta-4 with no validated equivalence. Safety trials of the full protein do not describe TB-500.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A 2026 review describes TB-500 as a distinct seven amino acid fragment of thymosin beta-4 that is often conflated with the full-length protein, with no validated biological or clinical equivalence. It reports concerns about the identity, purity, concentration, sterility and manufacturing consistency of commercial products [9]. A placebo-controlled safety trial of intravenous full-length thymosin beta-4 in healthy volunteers, given once and then daily for 14 days, reported infrequent mild or moderate adverse events and no serious adverse events [10].
Population
40 healthy volunteers in four cohorts of 10 [10]; products reviewed in [9].
Sources
[9], [10]
Caveats
The safety trial tested full-length thymosin beta-4, not TB-500, so it does not describe TB-500 [9][10].
LimitedHow often is not known

Unapproved drug warning letter

FDA states TB-500 products sold for research only are unapproved new drugs, and that injectable products can lead to serious conditions such as sepsis.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In a 2023 warning letter, FDA told a seller of injectable and nasal spray TB-500 that the products were unapproved new drugs, despite labels saying they were for research only and not for human consumption. FDA stated that injectable products bypass the body's natural defenses and can lead to serious and life-threatening conditions such as sepsis [11].
Population
Products sold to US consumers [11].
Sources
[11]
Caveats
A regulatory action, not a study of harm.
LimitedHow often is not known

Product contents

Limited evidence: one analysis found products sold online as TB-500 did not consistently contain what earlier descriptions said.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A 2012 analysis of a TB-500 formulation identified the acetylated 17 to 23 fragment of thymosin beta-4 (Ac-LKKTETQ) in it [12]. A 2023 analysis of products sold online as TB500 and TB1000 found that their content was not consistently what earlier descriptions of the products said [13].
Population
One TB-500 formulation [12]. Products sold online as TB500 and TB1000 [13].
Sources
[12], [13]
Caveats
Small numbers of products. The abstracts give no purity figures and report no tests for contaminants such as bacteria [12][13].
LimitedHow often is not known

Prohibited in sport

WADA lists TB-500 as prohibited at all times in sport.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
WADA lists thymosin beta-4 and its derivatives, naming TB-500, under S2.3, growth factors, prohibited at all times [14].
Population
Athletes subject to the World Anti-Doping Code [14].
Sources
[14]
Caveats
A sport rule, not a health finding.

Sources

  1. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. 2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
  2. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act. Updated April 22, 2026. 2026. https://web.archive.org/web/20260422215502/https://www.fda.gov/media/94155/download
  3. U.S. Food and Drug Administration. FDA Briefing Document: TB-500-Related Bulk Drug Substances (TB-500 (free base) and TB-500 acetate). Pharmacy Compounding Advisory Committee, July 23-24, 2026. 2026. https://www.fda.gov/media/193349/download
  4. Jacobus N. FDA Panel Votes to Loosen Restrictions for Four Peptides. Pharmaceutical Executive. 2026. https://www.pharmexec.com/view/fda-votes-loosen-restrictions-four-peptides
  5. Steinzor P. FDA Panel Backs 6 Peptides for Compounding. AJMC. 2026. https://ajmc.com/view/fda-panel-backs-6-peptides-for-compounding
  6. U.S. Department of Health and Human Services. Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances. Federal Register 91:68526. 2026. https://www.federalregister.gov/documents/2026/10/30/2026-22192/enforcement-discretion-policy-regarding-503a-compounding-using-certain-peptide-bulk-drug-substances
  7. U.S. Department of Health and Human Services. HHS Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances, with Appendices A and B. 2026. https://www.hhs.gov/sites/default/files/hhs-503a-peptide-enforcement-discretion-policy-appendix-b.pdf
  8. U.S. Food and Drug Administration. FDA Briefing Document: BPC-157-Related Bulk Drug Substances (BPC-157 (free base) and BPC-157 acetate). Pharmacy Compounding Advisory Committee, July 23-24, 2026. 2026. https://www.fda.gov/media/193343/download
  9. Tham A, Hodgkins CW, Kennedy JG. Investigational Peptides in Orthopaedic Practice: Evidence, Safety, and Patient Counseling for BPC-157, Thymosin Beta-4, and TB-500. Journal of the American Academy of Orthopaedic Surgeons. 2026. https://doi.org/10.5435/JAAOS-D-26-00049
  10. Ruff D, Crockford D, Girardi G, et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Annals of the New York Academy of Sciences. 2010. https://doi.org/10.1111/j.1749-6632.2010.05474.x
  11. U.S. Food and Drug Administration. Warning Letter: Warrior Labz SARMS, MARCS-CMS 655280. 2023. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/warrior-labz-sarms-655280-06122023
  12. 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 Testing and Analysis. 2012. https://doi.org/10.1002/dta.1402
  13. Delcourt V, Garcia P, Chabot B, et al. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Testing and Analysis. 2023. https://doi.org/10.1002/dta.3421
  14. World Anti-Doping Agency. The Prohibited List. 2026. https://www.wada-ama.org/en/prohibited-list
  15. Biçer O, Adanir O, Güleryüz Y, et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Joint Diseases and Related Surgery. 2026. https://doi.org/10.52312/jdrs.2026.2951
  16. Philp D, Badamchian M, Scheremeta B, Nguyen M, Goldstein AL, Kleinman HK. Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair and Regeneration. 2003. https://doi.org/10.1046/j.1524-475x.2003.11105.x
  17. Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. The actin binding site on thymosin beta4 promotes angiogenesis. FASEB Journal. 2003. https://doi.org/10.1096/fj.03-0121fje
  18. Ou H, Chen R, Zhou L, Zhang Y, Zhao S, Yang Z. Thymosin β4-derived peptides alleviate neuroinflammation and neurite atrophy in both in vitro models and in vivo 5 × FAD mice: A potential therapy for memory improvement in Alzheimer's disease. International Immunopharmacology. 2026. https://doi.org/10.1016/j.intimp.2025.116097

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