TB-500

DNot approvedthymosin beta-4 fragmentTB4Tβ4
In one paragraphTB-500 is a synthetic fragment of thymosin beta-4, a protein involved in cell migration and wound repair. Full-length thymosin beta-4 has been through phase 3 trials — as an eye drop for dry eye disease, with mixed results and no approval. The injected use people buy it for, for tendon and muscle injury, has never been tested in a completed human trial. It is banned in sport and not approved anywhere.
Schematic 3D structure of TB-500
43 residues · thymosin β4, intrinsically disordered · schematic
Overall gradeD No human evidence
Human trials0 for injected use
Outcomes graded4
Last reviewed2 September 2026
EvidenceWhat it isHow it worksUnknownsRegulationQuestionsReferences

What the human research shows

A case where human trials genuinely exist and are about something else entirely. The eye-drop programme tested a pharmaceutical-grade formulation on the ocular surface. Nothing in it speaks to injecting a vendor's fragment for a hamstring tear.

OutcomeGradeEffect sizeHuman studiesWhere the evidence comes from
Tendon, muscle & ligament healing (injected)DNo human evidenceNot measurable0 completedNo completed phase 2 or 3 randomised trial has tested systemic thymosin beta-4 or TB-500 for tendinopathy, muscle strain or ligament injury. Animal models in rodents and rabbits only.1
Dry eye disease (topical, RGN-259)BProbableSmall2 phase 3 RCTsARISE-1 and ARISE-2 tested a pharmaceutical eye drop. Improvements on some ocular-surface measures; primary endpoints not consistently met, and no approval followed.2
Cardiac repairDNo human evidenceNot measurableNoneMouse and pig infarct models only.
Safety in humans (injected)adverseDNo human evidenceNot measurableNone systematicNo systemic safety data. Independent testing of vendor products finds wide variation between labelled and actual content.
AMultiple good human trials, consistentBSome human trials, mostly consistentCFew or weak human studiesDAnimal or anecdotal onlyeffect size · red = adverse

Literature searched to 2 September 2026. Human studies only; animal and cell work informs the mechanism section and nothing else.

What it is

Thymosin beta-4 is a 43-amino-acid protein present in most human cells, where it binds actin and is involved in cell movement, blood-vessel growth and wound repair. TB-500 is a shorter synthetic fragment of it, marketed as a cheaper equivalent.

They are not the same thing, and the distinction matters when reading claims. RegeneRx developed pharmaceutical-grade thymosin beta-4 as RGN-259 and took it through phase 3 — as an eye drop. What is sold as TB-500 online may be the fragment or the full peptide, made to no particular standard.

How it is thought to work

By sequestering actin monomers it influences how cells crawl toward a wound, and it upregulates factors involved in new blood-vessel formation. That is well characterised in cell and animal work, which is why the injury claims sound mechanistically reasonable. Mechanism is not outcome.

What is still unknown

  • Whether injected TB-500 does anything for a human injury; the trial has not been run.
  • Whether the fragment behaves like the full protein at all in vivo.
  • What is in the vials, given the documented gap between label and content.

Regulatory status

European Union
Unapproved medicinal product

No authorisation. Sale for human use is an offence for the seller.

United States
Not approved

No FDA approval for any systemic indication; RGN-259 (ophthalmic) remains unapproved.

Sport (WADA)
Prohibited since 2012

Class S2, peptide hormones and growth factors — banned at all times.

Australia
Prescription-only or unapproved

Scheduled by the TGA; not available without a prescription.

Questions people actually ask

Does TB-500 heal injuries?
Unknown in humans. The healing evidence is from rodent and rabbit models. No completed randomised trial has tested it for a human tendon, muscle or ligament injury.
Is TB-500 the same as thymosin beta-4?
No. TB-500 is a shorter synthetic fragment. The phase 3 trials used full-length pharmaceutical-grade thymosin beta-4, and they were eye drops.
Is TB-500 banned in sport?
Yes, since 1 January 2012, under WADA class S2 — prohibited at all times, in and out of competition.

References

  1. 1
    Review of thymosin beta-4 / TB-500 clinical evidence: no completed systemic musculoskeletal RCT.Evidence review, 2026Secondary source; used for the absence-of-trials claim, which matches registry searches.
  2. 2
    RegeneRx. RGN-259 (thymosin beta-4 ophthalmic) ARISE-1 and ARISE-2 phase 3 trials in dry eye disease.Phase 3 programme; mixed endpoint results, no approvalThe only phase 3 human data for the parent molecule.

Change log

  • 2026-09-02Initial publication. Injected use graded D; ophthalmic programme graded separately at B.