What are the side effects of TB-500?

No controlled human study has been published, so no human side effect profile exists. Rodent work reports good tolerability, but that is short-duration animal data in another species.

Unknown in humans. The substantive concern is theoretical and follows from the mechanism: promoting cell migration and new vessel formation is not selective for the tissue you intend to help.

Does thymosin beta-4 safety data apply to TB-500?

Not directly. Thymosin beta-4 is a 43-residue protein; TB-500 is a seven-residue fragment. Findings about one do not automatically describe the other.

TB-500 (Thymosin β4 fragment)

TB-500 Side Effects: No Human Safety Record Exists

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-313 cited sources

No controlled human safety study of TB-500 has been published, so there is no reported side effect profile in people. Rodent work describes good tolerability. The substantive concern is theoretical and follows from the mechanism itself: a compound that promotes cell migration and new vessel formation is not selective about which cells it helps.

Key facts

Human safety trials: None published
Rodent tolerability: Reported as good
Mechanism concern: Migration is not selective
Anti-doping status: Prohibited by WADA
Compound studied: Often the protein, not the fragment

The honest answer is an absence

No published controlled trial reports adverse events for TB-500 in humans. Any list of side effects circulating online is either anecdote or extrapolation from animal work, and is rarely labelled as either. An absence of reported effects is not a safety finding; it reflects that the study which would report them has not been run.

A problem specific to this compound

Much of the safety literature people cite concerns thymosin beta-4, the full 43-residue protein. TB-500 is Ac-LKKTETQ, a seven-residue fragment. They are not the same molecule, and findings about one do not automatically describe the other. Checking which compound a cited study actually used matters more here than almost anywhere else in peptide research.

Research material referenced

TB-500 5mg — third-party HPLC tested

View — £23.99

What follows from the mechanism

TB-500's studied effects run through actin sequestration, cell migration and angiogenesis. Those are the properties that make it interesting for tissue repair, and they are not selective for tissue you want repaired. A systemic signal promoting migration and new vasculature is a reasonable thing to ask questions about, particularly over long periods. No study has demonstrated harm; equally, none has excluded it.

Sport is a separate question

TB-500 appears on WADA's prohibited list. That is independent of whether it is lawful to possess and independent of any safety finding — an athlete subject to testing should treat it as a distinct question with a clear answer.

And material is its own risk

Even where a molecule is well tolerated, poorly characterised material is not. Synthesis by-products, residual solvents and bacterial endotoxin attach to the material rather than the sequence, and none of them appears in a headline purity figure.

Extended research context

The TB-500 (Thymosin β4 fragment) deep dive

Deep dive: TB-500 vs full-length Thymosin Beta-4

'TB-500' is a synthetic peptide corresponding to the active 17-amino-acid actin-binding region of the endogenous 43-residue Thymosin Beta-4 protein. The two are not identical — TB-500 lacks the flanking sequence that gives full-length TB-4 additional binding partners. In the research literature, papers use 'Thymosin β4' when they mean the full protein and 'TB-500' or 'AcSDKP fragment' when they mean the shorter synthetic peptide. Reading a CoA carefully to see which molecule is in the vial matters — mass spec is the definitive check.

Actin-binding as the core mechanism

The N-terminal region of TB-4 (and TB-500 by inheritance) contains the canonical actin-binding motif. This motif sequesters G-actin monomers, modulating the G:F actin equilibrium in cell cultures. That mechanism is why almost every mechanistic paper on TB-500 traces back to cytoskeletal reorganisation, cell migration, and models of tissue repair.

Handling considerations unique to TB-500

TB-500 is a 17-residue peptide with modest amphipathicity; it reconstitutes cleanly in bacteriostatic water but is sensitive to repeated freeze/thaw. Aliquoting into single-use volumes on first reconstitution preserves potency across a batch. HPLC on the batch CoA should show a single dominant peak; a doublet suggests deamidation.

Research applications

▸In vitro actin-polymerisation assays (G:F actin ratio measurement)
▸Cell-migration and wound-scratch assays in fibroblast lines
▸Angiogenesis models: tube-formation and endothelial migration assays
▸Analytical method development for short peptides on RP-HPLC
▸Reference-material comparisons against endogenous Thymosin β4

Handling checklist

✓Store lyophilised vials at −20 °C long-term
✓Reconstitute with bacteriostatic water (0.9% benzyl alcohol)
✓Aliquot immediately to avoid freeze/thaw cycles
✓Refrigerate reconstituted aliquots at 2–8 °C; use within 28 days
✓Confirm mass (~4,963 Da for TB-500) via CoA before study use

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Assuming TB-500 = full Thymosin β4

Fix: TB-500 is the 17-residue actin-binding fragment; check the CoA sequence.

✗ Repeated freeze/thaw

Fix: Aliquot at first reconstitution; each cycle degrades yield.

✗ Using tap water

Fix: Use bacteriostatic or sterile water only.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

What are the side effects of TB-500?: No controlled human study has been published, so no human side effect profile exists. Rodent work reports good tolerability, but that is short-duration animal data in another species.
Is TB-500 safe?: Unknown in humans. The substantive concern is theoretical and follows from the mechanism: promoting cell migration and new vessel formation is not selective for the tissue you intend to help.
Does thymosin beta-4 safety data apply to TB-500?: Not directly. Thymosin beta-4 is a 43-residue protein; TB-500 is a seven-residue fragment. Findings about one do not automatically describe the other.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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