TB-500 (Thymosin Beta-4 fragment)
TB-500 (Thymosin Beta-4 fragment) — evidence, uses & status

Class: peptide
Synonyms: TB-500
"Thymosin Beta-4 fragment"
often marketed (loosely) as Thymosin Beta-4 / Tβ4 / TB4
thymosin beta-4
TB-4
note: TB-500 is a synthetic fragment of thymosin beta-4, not the same molecule
Function tags: tissue repair
wound healing
angiogenesis
anti-inflammatory (research context)
Overall evidence grade: C
WADA prohibited: yes
WADA note: Sport: WADA-prohibited at all times — Thymosin-β4 and its derivatives (e.g. TB-500) are named under Section S2 of the 2026 Prohibited List; detectable by LC-MS/MS. Athletes should treat it as banned.
Last updated: 2026-07-11

In brief: TB-500 is a synthetic actin-binding fragment related to Thymosin Beta-4, studied mainly in animal models for tissue repair, wound healing and inflammation. Importantly, the human clinical data belongs to full-length Tβ4 (mixed-result eye and cardiac trials, no approval), not to the TB-500 fragment — which has no completed human efficacy trials. It is not approved anywhere and is banned in sport.

## Identity **Thymosin Beta-4 (Tβ4)** is the natural **43-amino-acid** actin-sequestering peptide found in nearly every human cell. **"TB-500"** is a synthetic research/gray-market peptide reproducing Tβ4's **actin-binding region (LKKTETQ)** — the mechanistically active core. Sources disagree on its exact length (commonly described as a short acetylated fragment; some list ~17 aa), and many suppliers use "TB-500" and "Thymosin Beta-4" interchangeably even though they are **not the same molecule**. Both are < 43 aa → peptides. ## Development & history - **Thymosin Beta-4 (Tβ4)** was first characterised as a thymic peptide (Goldstein and colleagues) and later recognised as a ubiquitous actin-sequestering peptide involved in cell migration and repair.
- The pharmaceutical development has been of **full-length Tβ4**, chiefly by **RegeneRx Biopharmaceuticals** (with partners such as ReGenTree / G-treeBNT) — the **RGN-259** ophthalmic programme (dry eye, neurotrophic keratopathy; ARISE Phase 2/3, mixed results, orphan designation) and cardiac work — none of which reached approval.
- **"TB-500"** emerged separately as a research/gray-market **fragment**, used in **veterinary settings (notably racehorses)** and by athletes for recovery; the fragment itself never had a formal clinical-development programme. It features in several sports-doping cases and is now in the 2026 FDA compounding review. ## Mechanism (as proposed) the LKKTETQ core binds/sequesters **G-actin**, promoting **cell migration**, **angiogenesis**, tissue repair and an anti-inflammatory milieu. Most mechanistic detail comes from full-length Tβ4 biology and animal studies; whether the fragment reproduces these effects in humans is unproven.

Evidence grades by outcome:
outcome: Musculoskeletal / tendon / muscle recovery (the marketed use)
grade: C
base: Animal models only
effect: Suggestive tissue repair
caveat: Preclinical; no completed human efficacy trial for the fragment
outcome: Wound healing / corneal repair
grade: C
base: Human trials of full-length Tβ4 — RGN-259 ophthalmic Phase 2/3 (ARISE-1/2); Philp 2003 corneal
effect: Mixed; some benefit, primary endpoints not fully met
caveat: Data is on Tβ4, not TB-500; no FDA approval; orphan designation only (neurotrophic keratopathy)
outcome: Cardiac repair
grade: C
base: Animal models + an early Tβ4 RCT
effect: Suggestive
caveat: Full-length Tβ4; early-stage
outcome: Marketed "recovery stack" (with BPC-157) for human injury/performance
grade: F
base: None
effect: Not demonstrated
caveat: No human RCT for the injuries the stack targets
outcome: Safety & long-term
base: Limited human data for the fragment; theoretical concern from pro-angiogenic activity
effect: Unknown
caveat: WADA-banned; long-term/oncologic safety not established

Legal status:
region: EU
status: Not approved
note: Not approved for human use; not eligible for magistral/officinal compounding (no Ph. Eur. monograph). Sold only as a non-medicinal "research" chemical, which does not authorise human use.
region: US
status: Not FDA-approved (under review)
note: Removed from 503A Category 2 in April 2026; on the PCAC agenda for 23 July 2026 (with BPC-157) for possible 503A Bulks-List inclusion; FDA's pre-meeting briefing documents proposed not adding it. Advisory only; no Federal Register rule as of this writing. Full-length Tβ4 sits on a separate drug track (see below).
region: INT
status: Approved nowhere
note: Approved nowhere.

Cosmetic claims:

Note: Research / reference — not for sale. No dosing, reconstitution, or administration is published (intentional). Neutral scientific reference only. Note the identity distinction below — "TB-500" and full-length Thymosin Beta-4 are related but not identical, and it matters for reading the evidence.
Status note: US review status evolving — re-check the July PCAC outcome and any Federal Register rule

Sources:
Goldstein AL, Hannappel E, Kleinman HK. Thymosin β4: actin-sequestering protein moonlights to repair injured tissues. (Tβ4 biology review.)
Philp D, et al. Thymosin β4 and corneal wound healing. 2003.
RegeneRx / ReGenTree. RGN-259 (Tβ4) ophthalmic ARISE-1/ARISE-2 trials (NCT02597803, NCT02974907); acute MI trial (NCT01311518).
Thymosin Beta-4 and TB-500 in tissue healing and musculoskeletal repair: a scoping review. Appl Sci. 2026.
WADA. 2026 Prohibited List, Section S2.