TB-500 / thymosin beta-4 fragment

Not FDA-approved Evidence grade D — animal or in-vitro data only Updated 2026-10-20

This page describes published research and public regulatory records. It is not medical advice. SoluneFit does not sell, supply, or recommend any compound. The SoluneFit app includes a private, on-device tracker for people who want a record of what they and their clinician have already decided — the app neither suggests compounds nor doses.

Also known as: TB-500, TB 500, TB500, Ac-LKKTETQ, thymosin beta-4 fragment 17-23, TB-500 acetate, thymosin beta 4, Tβ4.

Regulatory status

Not approved and not a component of any FDA-approved drug. FDA's briefing for the 23-24 July 2026 PCAC proposed NOT adding TB-500 (free base or acetate) to the 503A bulks list, citing poor characterisation, no human data and immunogenicity risk [1][2]; PCAC outcome UNVERIFIED: FDA has posted no minutes or vote summary as of 2026-10-20 (non-FDA reports describe a non-binding vote for inclusion, rulemaking pending). FDA's compounding-risk page lists it as nominated then withdrawn, with no human exposure data [3]. FDA has treated TB-500 sold for human use as an unapproved new drug (warning letter, 2023) [4].

What it is

Synthetic N-acetylated 7-amino-acid fragment (residues 17-23, Ac-LKKTETQ) of thymosin beta-4, the 43-amino-acid actin-binding protein.

A short synthetic piece of thymosin beta-4, the part that binds actin, sold for tissue and tendon repair. FDA notes TB-500 and full-length thymosin beta-4 are different substances, and no study has given TB-500 to humans.

What the published research shows

No human studies of TB-500 by any route (FDA search). Evidence is in-vitro work and animal studies, mostly on full thymosin beta-4 or the unacetylated fragment; horse data are drug-testing PK only.

Published human studies and reports (these describe trial populations, not SoluneFit claims):

Horse doping-control study (Ho et al. 2012): Single SC dose of TB-500 containing 10 mg of N-acetylated LKKTETQ; parent peptide and metabolites detected in plasma (limit 0.02 ng/mL) and urine.
Aged-mouse wound model (Philp 2003, as summarised by FDA): Topical unacetylated LKKTETQ 0.01 % improved skin closure and collagen at day 7; no dose-response tested.
Compounding nomination (withdrawn): 3 mg/mL lyophilised powder for SC or IM injection for wound healing; no dosing regimen was given.

Mechanism, as reported

Not established for TB-500 itself. The LKKTET region of thymosin beta-4 binds actin and is linked to cell migration in lab and animal work; in one lab study TB-500 did not speed fibroblast wound closure.

Practical record

Elimination half-life: 2.0 h (confidence: low). No TB-500 half-life is published for any species, so 2 h is a placeholder. In horses given 10 mg SC, plasma levels peaked at 1-2 h and were unquantifiable by 6-10 h (Ho 2012, as summarised by FDA), which a 2 h half-life roughly reproduces. No human PK. Treat the curve as a guess.
Studied routes: subcutaneous, intramuscular.
Typical supply: No approved product. Sold online as 2-15 mg 'research use only' lyophilised vials (FDA).
Reconstitution: Water-soluble (supplier data cited by FDA); no published in-use stability.
Storage: Powder -20 °C (1 year) or -80 °C (2 years); acetate 2-8 °C per one certificate of analysis (supplier data cited by FDA).

Safety signals on record

Reported adverse events: No human safety studies. FDA found no adverse-event reports and two food-complaint cases involving blended TB-500/BPC-157 with no detail.
Contraindications: None established (no label).
Interactions: None documented.
Notes: No toxicology studies of any kind (acute, repeat-dose, genetic, reproductive, cancer). FDA's main concern is immune reactions to injected peptide and impurities, including antibodies that might act against the body's own thymosin beta-4. Prohibited in sport (WADA S2, per FDA).

Sources

General wellness education, not medical advice. Unapproved compounds have no established dosing, purity standard, or safety profile.

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