TB-500 Side Effects: What the Evidence Shows

What is actually known about TB-500 safety

The honest headline is a gap. This research surfaced no human trial of the TB-500 fragment to draw a side effect list from. The human evidence that exists is about full thymosin beta-4, the parent protein.¹⁵ The cell findings concern that protein too (PMID 16364925, PMID 17072345, PMID 21621326). These findings do not establish the safety of the TB-500 fragment. So this page reports mostly what has been measured for the parent molecule and for detection in animals, and it marks every place where the fragment itself has not been tested.

If you want the compound itself rather than its safety record, the TB-500 profile covers what it is and how people use it, and the Wolverine stack guide covers running it with BPC-157. This page stays on the safety question. For the wider picture of how approved and unapproved peptides differ on side effect data, the peptide side effects by class guide sets the frame. For more reading, see the guide to MOTS-c side effects.

A fragment, not the whole protein

This distinction decides how to read everything below. Full thymosin beta-4 is a naturally occurring 43 amino acid peptide.⁵ TB-500 is not that molecule. It emerged as a veterinary preparation containing a synthetic version of the seven residue segment LKKTETQ, positions 17 to 23 of thymosin beta-4, which is the region responsible for actin binding, cell migration and wound healing.⁶ The key ingredient of TB-500 is that segment with an artificial acetyl group on the N-terminus, written Ac-LKKTETQ.⁶⁷

Because the human trials below used the full 43 amino acid protein, their safety findings cannot simply be transferred to the 7 residue TB-500 fragment. Those trials therefore do not establish the safety profile of the TB-500 fragment, and no study in this research bridged that gap. Every time this page quotes a thymosin beta-4 result, read it as data on the parent protein, not a measurement of TB-500.

The human trials used thymosin beta-4, not TB-500

Here is the human record. Every figure in the table is a trial figure for full thymosin beta-4, not a recommendation and not a TB-500 dose. These studies were small and short, and the neurotrophic keratopathy phase 3 lists authors employed by the developer, ReGenTree, which is a real limit on how much they establish.⁴

The intravenous study tested full thymosin beta-4 in healthy people. Four cohorts of 10 received single ascending intravenous doses of 42, 140, 420 or 1260 mg of synthetic thymosin beta-4 or placebo, then the same dose daily for 14 days (trial dose, not a recommendation, PMID 20536472), and the authors reported that adverse events were infrequent and mild or moderate, with no dose limiting toxicities and no serious adverse events.¹ In the dry eye phase 2, subjects were randomized to placebo or a 0.1% ophthalmic solution for 28 days (trial dose, not a recommendation, PMID 26056426), and the trial reported no adverse events observed.² In the small severe dry eye trial, patients received vehicle or a 0.1% solution six times daily for 28 days (trial dose, not a recommendation, PMID 25826322), and the authors described the drops as well tolerated.³ A phase 3 in neurotrophic keratopathy reported in its abstract only that no significant adverse effects were observed, while its full text records 16 adverse events across 7 of 18 subjects, one of them judged treatment related, including one non-ocular serious adverse event judged unrelated to treatment, and its author list includes employees of the product developer.⁴¹³ A topical venous ulcer trial in 73 patients reported the safety of all doses as acceptable and comparable to placebo.⁵

One caveat on the registry trail. A ClinicalTrials.gov entry for an intravenous phase 1 of thymosin beta in healthy volunteers, NCT00743769, is listed as withdrawn, and it could not be matched to the published intravenous study above, so this page cites that study by its publication only and does not present the withdrawn registry entry as its registration.¹¹

No human trial of the TB-500 fragment surfaced in this research

The TB-500 specific studies that were retrieved are not safety trials at all. They are doping control chemistry: a method that detected the acetylated fragment in horse urine and plasma,⁶ and a paper that synthesized and characterized the N-terminal acetylated 17 to 23 fragment identified in TB-500, a product it describes as suspected of doping potential.⁷ No human clinical trial of the fragment itself surfaced in this research, which is itself the central finding rather than a footnote. That null has a stated limit: the searches behind it were a web search and a PubMed search, and a ClinicalTrials.gov registry search for TB-500 was not run for this research file, so the finding covers what was searched, not every registry.

Product quality is a separate question, and this page will not guess at it. No source fetched for this guide tested the purity, contamination or labelling accuracy of any specific TB-500 product, so it makes no claim about product quality in either direction. Whatever the source, a published certificate of analysis for the exact batch is worth reading, and how to verify a peptide certificate of analysis explains what to look for. A certificate does not by itself establish that a product is safe.

Cell studies and the cancer question

The safety questions that reach past the human trials come from biology, and they need careful reading because they concern the full protein, not the TB-500 fragment. Thymosin beta-4 is described as stimulating angiogenesis, the growth of new blood vessels,⁵ and the doping-control paper describes a claim that TB-500 promotes angiogenesis in dermal tissues (doping-control chemistry, not a human trial, PMID 23084823).⁶ The cell studies below concern the full protein and are worth stating plainly rather than burying.

Read those carefully. They are overexpression experiments, forcing cancer cells to make more of the full thymosin beta-4 protein, not studies of the TB-500 fragment in an animal or a person.⁸⁹¹⁰ No direct evidence that TB-500, the fragment, promotes tumours in animals was found in this research. That is not reassurance, it is an unanswered question: the mechanism is documented for the parent protein, while no study fetched here tested the fragment for that effect.

Doping status: what USADA confirmed

For an athlete, the clearest fact on this page is a regulatory one. According to USADA, in its summary of the 2018 Prohibited List dated October 2, 2017, thymosin-beta4 and its derivatives, for example TB-500, were added as examples of prohibited growth factors under section S2.3.¹² The fragment is also detectable in testing: the doping control method confirmed the acetylated peptide at 0.02 ng/mL in equine plasma and 0.01 ng/mL in equine urine (doping-control detection, horses, PMID 23084823).⁶

We could not verify the current 2026 wording of the WADA Prohibited List for this page, because the live list could not be retrieved during research, so this page states only the 2018 addition that USADA confirmed and does not assert the present classification beyond it. Anyone subject to testing should read the current list directly rather than rely on a summary.

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TB-500 emerged as a veterinary preparation containing a synthetic version of the thymosin beta-4 fragment, and no human trial of the fragment surfaced in this research.⁶ For TB-500, this page links to our supply partner, Peptara Labs.

The short version

Every study figure on this page traces to one of these sources, fetched on 2026-09-30. Numbers match the citation markers in the text.