What is TB-500?

TB-500 is a synthetic peptide named after thymosin beta-4, a 43-amino-acid protein that binds actin in cells. The analytical literature identifies TB-500 as an acetylated short fragment of that protein. As of 23 September 2026, its research is in animals and cells only; human trials used the full-length protein instead.

Primara Labs sells some of the compounds covered here. Every figure on this page links to its source and the date it was checked.

Updated 23 September 2026

The molecule

Thymosin beta-4 is a 43-amino-acid protein and the main actin-sequestering molecule in cells. Its central actin-binding sequence, LKKTETQ, is reported to promote cell migration, new blood vessel growth and wound healing, and TB-500 is described in the analytical literature as the acetylated form of that fragment. A 2024 cell study found the wound-healing activity came from a TB-500 breakdown product rather than TB-500 itself.

That distinction matters because a product sold as TB-500 and a product sold as thymosin beta-4 are not the same substance, and results for one do not describe the other.

What the animal and cell work found

In aged and diabetic mice, the seven-amino-acid thymosin beta-4 fragment LKKTETQ promoted skin wound repair about as well as the full-length protein. This was in mice.

In a cell scratch-wound test, the TB-500 breakdown product Ac-LKKTE showed wound-healing activity, while TB-500 itself did not. This was in cells in a dish.

Animal and cell studies only for TB-500. Human trials exist for full-length thymosin beta-4, a different molecule, mostly as eye drops; see the Evidence Map.

Human data

No human adverse event data exist for TB-500. In the phase 3 trial of full-length thymosin beta-4 eye drops (ARISE-3), a different molecule, instillation site pain occurred in 6.6% against 4.6% on placebo.

The US FDA lists the fragment on its compounding safety-risk page and states that it has not identified human exposure data. The Research Desk rates TB-500's evidence as animal and cell.

The papers behind it

Animal and cell studies only for TB-500. Human trials exist for full-length thymosin beta-4, a different molecule, mostly as eye drops; see the Evidence Map.

Wound Repair Regen 2003: In aged and diabetic mice, the seven-amino-acid fragment LKKTETQ promoted skin wound repair about as well as full-length thymosin beta-4.

J Chromatogr B 2024: In a cell scratch-wound test, only the TB-500 breakdown product Ac-LKKTE showed wound-healing activity, not TB-500 itself.

Jt Dis Relat Surg 2026: A rat Achilles tendon repair study described its molecule as synthetic thymosin beta-4 (TB-500) without stating the sequence in the abstract.

Sources

Where every figure comes from

Thymosin beta-4 and TB-500 source · checked 23 September 2026
Wound Repair Regen 2003 · checked 23 September 2026
J Chromatogr B 2024 · checked 23 September 2026
ClinicalTrials.gov NCT03937882 results · checked 23 September 2026

Last reviewed 23 September 2026