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New to Peptides · Part 2: The best-known peptides today

TB-500 (thymosin beta-4)

Lesson 12.2.5 · 4 min read · Free lesson

Where it stands: early human data only, not approved (yellow, close to red).

Thymosin beta-4 is a natural protein found in almost every cell. It helps cells move and change shape 14. "TB-500" is a lab-made product sold online, usually described as a short piece of thymosin beta-4. What's in the vial varies 11.

How strong is the evidence?

Nearly all human studies tested the full natural protein, not TB-500, mostly as eye drops or skin gel 14. Results were mixed. In a small trial of eye drops for a hard-to-heal eye condition, more treated eyes healed, but the result narrowly missed statistical proof 15. The FDA says it found no human safety data for the TB-500 fragment itself 11.

Safety and rules

Lab studies link high thymosin beta-4 levels to tumor growth in some cancers, which is a theoretical concern 14. Like BPC-157, it's covered by the temporary October 2026 HHS compounding policy, which is not an approval 12. It's banned in sport at all times 13.

The honest takeaway

The studies people quote were done on a different product (the full protein), and even those were small.

Check what you learned: take this lesson's quick quiz in the Academy. It is free.

Sources

  1. DailyMed - WEGOVY (semaglutide) injection and tablets, prescribing information (revised 6/2026)
  2. Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med 2021
  3. Lincoff AM et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med 2023
  4. FDA approval letter - Wegovy (semaglutide) tablets, NDA 218316 (Dec 22, 2025)
  5. FDA label - ZEPBOUND (tirzepatide) injection, revised 04/2026
  6. Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med 2022;387(3):205-216
  7. Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med 2023
  8. AJMC - Retatrutide achieves up to 30.3% average weight loss in phase 3 TRIUMPH-1 trial (May 2026)
  9. Józwiak M, Bauer M, Kamysz W, Kleczkowska P. Multifunctionality and Possible Medical Application of the BPC 157 Peptide - Literature and Patent Review. Pharmaceuticals 2025;18(2):185
  10. 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 (PMID 34324435)
  11. FDA - Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 04/22/2026)
  12. HHS - Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances (policy text with appendices, October 2026)
  13. World Anti-Doping Agency - Prohibited List 2026
  14. Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin beta4: a multi-functional regenerative peptide. Expert Opin Biol Ther 2012 (PMID 22074294)
  15. Sosne G, Kleinman HK, Springs C, et al. 0.1% RGN-259 (thymosin beta 4) ophthalmic solution in neurotrophic keratopathy (SEER-1). Int J Mol Sci 2023;24(1):554
  16. Pickart L, Margolina A. Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data. Int J Mol Sci 2018;19(7):1987
  17. Teichman SL et al. Prolonged stimulation of GH and IGF-I secretion by CJC-1295, a long-acting analog of GHRH, in healthy adults. J Clin Endocrinol Metab 2006
  18. FDA briefing document, Pharmacy Compounding Advisory Committee, Dec 4, 2024: CJC-1295-related bulk drug substances
  19. Beck DE et al. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for postoperative ileus in bowel cancer resection patients. Int J Colorectal Dis 2014
  20. FDA briefing document, Pharmacy Compounding Advisory Committee, Oct 29, 2024: ipamorelin and ipamorelin acetate
  21. Vyleesi (bremelanotide injection) Prescribing Information - FDALabel
  22. Healio - FDA approves Vyleesi for women with low sexual desire (June 21, 2019)
  23. FDA label - RYBELSUS (semaglutide) tablets, 2026

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