Peptides
TB-500 fragment (889 Da): why it differs from full-length TB4
What is it?
A product labeled TB-500 fragment (889 Da) points to N-acetyl-LKKTETQ, the seven-amino-acid 17–23 region of full-length thymosin beta-4 (TB4). The short fragment and full-length peptide differ in size and chemistry. Results from the full-length peptide cannot be attributed to the fragment without direct testing. [1]
What do studies show?
Analytical work has identified the acetylated fragment in products sold as TB-500, but chemical identification is not a demonstration of healing. The FDA’s 2026 evidence review found no clinical studies or human exposure data for TB-500 by any route. Claims about tendon repair, exercise recovery, or wound healing in people remain unproven for this exact 889 Da product. [1,2]
Safety
No human adverse-event rate or reliable benefit-risk balance is known. FDA notes concerns about peptide impurities and immunogenicity in compounded versions. Product identity should be verified by lot-level analytical testing; a 10 mg label alone does not do that. [1]
DOSE STATUS
How much?
EVIDENCE CONTEXT
Why?
The cited evidence does not establish a dose for this use or product.
No established safe/effective human dose of the TB-500 fragment exists. Full-length TB4 trial amounts and anecdotal “TB-500” protocols often fail to distinguish the molecule, so they cannot responsibly be converted into a fragment dose. The 10 mg vial is a package amount only. [1,2]