TB-500

DNot approvedTissue-repair peptides →thymosin 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 worksUnknownsMolecule & PKRegulationQuestionsReferences

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.

MetabolicCardioMuscleHealingNeuroImmuneSexualSkinAgeing

Evidence profile0–5

  • Metabolic & weight—0.0
  • Cardiovascular—0.0
  • Muscle & growth—0.0
  • Healing & repairB1.2
  • Neuro & sleep—0.0
  • Immune & inflammation—0.0
  • Sexual & hormonal—0.0
  • Skin & appearance—0.0
  • Ageing & longevity—0.0
Each score is confidence × effect size, taken from the best-evidenced benefit in that domain: the grade (A–D) sets the confidence, the measured effect sets the size. Hover a domain to see the outcomes behind it. Adverse effects are excluded and listed separately below.
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.

Registered trials

ClinicalTrials.gov lists 1 interventional study naming TB-500 as an intervention, 1 recruiting, and none with results posted to the registry.

A registration is not a result. Anyone can register a study, and many never report — so this list shows what has been attempted, not what has been shown. The graded evidence above is the answer to whether something works.

StudyPhaseStatusParticipantsSponsorResults
TB-500 (Thymosin Beta 4 17-23 Fragment) for Cardiovascular Biomarkers in Stable ASCVDNCT07487363 · started Feb 2026Phase 1Recruiting80*Hudson BiotechNone

Participant counts marked * are the sponsor's estimate, not a final enrolment. Source: ClinicalTrials.gov, read directly from the registry and refreshed weekly.

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.

The molecule and how long it lasts

Identity
Formula
C212H350N56O78S
Molecular weight
4963 g/mol
CAS number
77591-33-4
PubChem
CID 16132341

PubChem record is full-length thymosin β4 (timbetasin); TB-500 as sold is a fragment of it

PubChem record, read 23 September 2026.

Pharmacokinetics
Route
Intravenous in the only human study (full-length thymosin β4, healthy volunteers)
Half-life
Measured but not reported as a figure; the abstract says half-life increased with dose

From a published human pharmacokinetic study: Ruff D, et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci 2010

Regulatory status

European Union
Unauthorised medicinal product

No marketing authorisation in any member state. Supplying it for human use is an offence under national medicines law; 'research use only' labels do not change that.

United States
Not approved; compounding under review

Removed from FDA's Category 2 list on 22 April 2026; the Pharmacy Compounding Advisory Committee recommended it for the 503A bulks list in July 2026 (8–6, 1 abstention). Not on the list yet and not an approved drug. Sold otherwise as an unapproved 'research chemical'.

United Kingdom
Unlicensed medicine

Not licensed by the MHRA. Selling or supplying it is an offence under the Human Medicines Regulations 2012; importing a small quantity purely for personal use is not itself an offence, but consignments are seized.

Australia
Schedule 4, unapproved

Prescription-only substance not on the ARTG. Obtainable only on prescription (compounded or imported under the Personal Importation Scheme with a prescription). Named in the TGA's April 2026 advisory. Named in NSW law as a prescribed restricted substance.

Canada
Not authorised

No Drug Identification Number; selling it is illegal. Among the products Health Canada seized from a domestic vendor in August 2025. Residents cannot import prescription drugs by mail.

Sport (WADA)
Prohibited at all times

S2.3: 'thymosin-β4 and its derivatives, e.g. TB-500'.

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.

One page per claimed effect

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.