TB-500 guide
This TB-500 guide starts with the thing most pages about it skip. TB-500 and thymosin beta-4 are not the same molecule: TB-500 is a seven-amino-acid fragment covering positions 17 to 23 of the full 43-amino-acid peptide, and FDA says so explicitly, noting that websites often use the two names interchangeably1. That matters because every completed human trial used the full molecule, not the fragment.
The short answer
- What it is: a synthetic fragment of thymosin beta-4, sold under a name that is not an official drug name1.
- Human evidence for TB-500 itself: none. FDA reports finding no published study in which TB-500 was given to a human11412.
- Human evidence for thymosin beta-4: real, and mostly negative. Two phase 3 trials in 1,301 people failed every primary measure56.
- Approved? No. FDA proposed against allowing it in compounding, citing a lack of evidence of effectiveness12.
- Prohibited in sport at all times, with the rule explicitly covering derivatives so the fragment-versus-molecule distinction offers no exemption4.
Why the distinction is not pedantic
Trials of thymosin beta-4 are routinely cited in marketing for TB-500. They are studies of a different substance: the eye-drop trials used full-length thymosin beta-4, as did the wound gels, the withdrawn injectable programme, and the recombinant product tested in healthy volunteers.
FDA also found that TB-500 is not well characterised chemically, that the name covers more than one substance in commerce, and that suppliers use a single identifier for materials that are chemically different1. In practice that means two vials labelled TB-500 need not contain the same thing.
The first registered human study of TB-500 itself began recruiting in 2026. It is a safety and tolerability study, it has no results, and nothing can be claimed from its existence11412.
What happened when thymosin beta-4 was actually tested
It was tested properly, several times, and largely did not work. The two phase 3 dry-eye trials are the clearest result in this entire library: 700 participants in one and 601 in the other, and neither separated from placebo on either of its two main measures. In both cases the treated group was, if anything, marginally worse56.
Two smaller trials are worth reading carefully, because they are cited as positive. A 72-person phase 2 trial missed both of its primary measures and was published with the conclusion that it confirms efficacy, a claim resting entirely on secondary measures. A phase 3 trial in corneal disease, terminated at 18 participants for business reasons, reported healing in 6 of 10 treated against 1 of 8 on placebo, a difference that did not reach statistical significance, and was published under a title stating that the treatment promotes healing78.
In wound healing the picture is no better. Venous ulcers closed in 21.8 per cent of treated participants against 23.5 per cent on placebo, and in a trial in a genetic skin-fragility condition, healing was numerically worse in the treated group109.
The most-cited positive human result is a trial in nine patients with severe dry eye1165. It is the smallest study in the programme, and the two much larger trials that followed did not reproduce it.
The cardiac story, and where it stopped
A 2004 paper in Nature reported that thymosin beta-4 improved heart muscle survival and function in mice after a tied coronary artery, working through a specific signalling route15. It is a genuinely influential piece of work and it is the origin of most cardiac claims made about this family.
What is usually left out: the injectable human cardiac programme built on it was withdrawn before it enrolled a single patient, and no completed human cardiac trial of either molecule has reported results15.
Tendon, muscle, and the claims made for athletes
One controlled rat study tested TB-500 itself in repaired Achilles tendons, and it was the only treatment in that study to reach statistical significance on tendon strength16. That is a real result, in eight rats per group, over four weeks, described as exploratory by its own authors.
There is no human tendon or ligament trial of either molecule. An orthopaedic systematic review covering this compound alongside others concluded that about two thirds of the literature is preclinical, that human studies are few and mostly lack robust controls, and that the claimed musculoskeletal benefits remain unsubstantiated by human trials1716. For muscle repair specifically, no controlled study of TB-500 was identified in any species[unverified].
How it behaves in the body
For TB-500 there is no human pharmacokinetic data at all11412. For full-length thymosin beta-4 given intravenously there is: it peaks within minutes and has a half-life of roughly half an hour to two hours, rising with dose1213.
The usual explanation for how the fragment works is that it binds actin. FDA describes this as a hypothesis and states that it remains to be determined whether actin binding accounts for the effects attributed to the fragment1.
Where the rest of the detail lives
The interactive library on the homepage carries the fuller reference entry for TB-500, including the amounts and handling notes it holds for every compound. That is general reference information, the same for every visitor.
References
These are the sources behind this page, listed so you can read them yourself rather than take our word for it. Animal and laboratory findings do not establish that something works or is safe in people. Doses and protocols shown on a study card are that study's research parameters, not recommendations. PepCaddie does not sell peptides and does not choose a dose for anyone; this is educational material and it does not replace a qualified healthcare professional.
ARISE-3, phase 3 dry-eye trial that missed both endpoints
2021Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
The largest trial of thymosin beta-4 ever completed. Neither of its two main measures separated from placebo: corneal staining improved slightly more on placebo, and ocular discomfort improved identically in both groups.
Limitation: The posted results give group means without a statistical test, so the failure is read from overlapping results rather than a published p-value. The trial has never been published in a journal.
Randomised, quadruple-masked, placebo-controlled phase 3 trialView study: ARISE-3, phase 3 dry-eye trial that missed both endpoints
ARISE-2, phase 3 dry-eye trial that missed both endpoints
2018Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
The other large phase 3 dry-eye trial. Both main measures failed, with the treated group numerically slightly worse on each.
Limitation: As with ARISE-3, no inferential statistics are posted and the trial was never published.
Randomised, quadruple-masked, placebo-controlled phase 3 trialView study: ARISE-2, phase 3 dry-eye trial that missed both endpoints
Phase 2 dry-eye trial: both primary endpoints missed
2015Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
Neither of the two primary measures showed a significant difference against placebo. Several secondary measures did.
Limitation: Worth knowing when this paper is cited as supportive: its stated conclusion is that the trial confirms efficacy, a claim resting entirely on secondary measures after both primary measures failed.
Randomised, double-masked, placebo-controlled phase 2 trialView study: Phase 2 dry-eye trial: both primary endpoints missed
SEER-1, terminated phase 3 trial in corneal disease
2022Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
Six of ten treated participants healed against one of eight on placebo, a difference that did not reach statistical significance. The trial was terminated for business reasons after enrolling 18 of an intended phase 3 population.
Limitation: The published title states the treatment promotes healing, which the trial’s own result does not establish at this sample size.
Randomised, double-masked, placebo-controlled phase 3 trial, terminated earlyView study: SEER-1, terminated phase 3 trial in corneal disease
Terminated trial in epidermolysis bullosa
2012Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
A safety trial that also recorded healing. Wounds healed in 8 of 22 treated participants against 5 of 8 on placebo, so healing was numerically worse in the treated group. The trial stopped early because of difficulty recruiting and expiry of the study drug.
Limitation: Small, terminated, and designed around safety rather than powered to detect an effect on healing.
Randomised, double-blind, placebo-controlled trial, terminated earlyView study: Terminated trial in epidermolysis bullosa
Venous ulcer trial: no benefit over placebo
2009Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
Wounds closed in 21.8 per cent of treated participants against 23.5 per cent on placebo. The trial’s main purpose was safety, and adverse events were more frequent in the treated arms.
Limitation: No statistical analysis of healing is posted, and any positive claim from this programme rests on subgroups defined by dose after the fact.
Randomised, double-blind, placebo-controlled trialView study: Venous ulcer trial: no benefit over placebo
Small positive trial in severe dry eye
2015Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
Discomfort and corneal staining both improved significantly against the vehicle. This is the most frequently cited positive human result for thymosin beta-4.
Limitation: Nine patients. It is also the smallest trial in the programme, and the two much larger phase 3 trials that followed did not reproduce the effect.
Randomised, double-masked, placebo-controlled phase 2 trialView study: Small positive trial in severe dry eye
First-in-human pharmacokinetics of recombinant thymosin beta-4
2021Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
The clearest human pharmacokinetic data in this family. Given intravenously, recombinant thymosin beta-4 peaked within 3 to 15 minutes and had a half-life between about half an hour and two hours, rising with dose. Adverse events were mild to moderate.
Limitation: Healthy volunteers, intravenous only, and full-length recombinant thymosin beta-4 rather than TB-500. It measured no clinical outcome.
Randomised, double-blind, placebo-controlled phase 1 trialView study: First-in-human pharmacokinetics of recombinant thymosin beta-4
Earlier phase 1 safety study
2010Human randomised trial
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
Adverse events were infrequent and mild to moderate, with no dose-limiting toxicity. Blood levels rose in proportion to dose and the half-life grew as the dose grew.
Limitation: The published abstract reports no numeric pharmacokinetic values. Doses here are in milligrams, thousands of times larger than the microgram-per-kilogram doses in the later recombinant study, so the two cannot be compared.
Randomised, placebo-controlled phase 1 trialView study: Earlier phase 1 safety study
The foundational animal cardiac study
2004Animal studyNot human evidence
The paper behind most cardiac claims about this family. In mice with a tied coronary artery, thymosin beta-4 improved heart muscle cell survival and heart function, working through a signalling route involving integrin-linked kinase.
Limitation: Mice, and full-length thymosin beta-4 rather than TB-500. Two decades later, the injectable cardiac programme it inspired was withdrawn before enrolling a single patient, and no completed human cardiac trial has reported.
Controlled animal and cell experimentsView study: The foundational animal cardiac study
Rat tendon study comparing TB-500 with BPC-157
2026Animal studyNot human evidence
The dose above is the amount used in this study. It is research information, not a recommended dose, and PepCaddie does not convert study doses into human doses.
One of very few controlled studies of TB-500 itself. In repaired rat Achilles tendons, TB-500 was the only treatment to reach statistical significance on tendon strength. Combining it with BPC-157 added nothing over either alone.
Limitation: Eight rats per group, a single four-week timepoint, and described by its own authors as exploratory. It is an animal study, and there is no human tendon trial of either compound.
Randomised controlled animal experiment, four groupsView study: Rat tendon study comparing TB-500 with BPC-157
Systematic review of peptides in sports medicine
2026Systematic review
An orthopaedic review covering TB-500 and thymosin beta-4 alongside BPC-157, ipamorelin and others. It found that about two thirds of the literature is preclinical, that human studies are few and mostly lack robust controls, and that the claimed musculoskeletal benefits remain unsubstantiated by human trials.
Limitation: A review summarises existing work rather than adding new evidence, and it covers several compounds rather than examining any one in depth.
Systematic reviewView study: Systematic review of peptides in sports medicine
Pharmacy Compounding Advisory Committee briefing document: TB-500-related bulk drug substances. U.S. Food and Drug Administration; 2026.
Official regulatory sourceChecked 2026-09-21
Read FDA's 2026 review of TB-500 for compounding at the sourceCertain bulk drug substances for use in compounding that may present significant safety risks. U.S. Food and Drug Administration; 2026.
Official regulatory sourceChecked 2026-09-21
Read FDA's compounding safety-risk list at the sourceWarning letter: Warrior Labz SARMS (MARCS-CMS 655280). U.S. Food and Drug Administration; 2023.
Official regulatory sourceMARCS-CMS 655280Checked 2026-09-21
Read FDA warning letter to a TB-500 seller at the sourceThe 2026 Prohibited List, World Anti-Doping Code. World Anti-Doping Agency; 2026.
Official regulatory sourceChecked 2026-09-21
Read WADA's 2026 Prohibited List, section S2.3 at the sourceA multi-center, randomized, double masked, placebo controlled clinical study to assess the safety and efficacy of RGN-259 ophthalmic solutions for the treatment of dry eye (ARISE-3). ClinicalTrials.gov, sponsor ReGenTree LLC; 2021.
Human randomised trialNCT03937882Checked 2026-09-21
Read ARISE-3, phase 3 dry-eye trial that missed both endpoints at the sourceA multi-center, randomized, double masked, placebo controlled clinical study to assess the safety and efficacy of RGN-259 ophthalmic solutions for the treatment of dry eye (ARISE-2). ClinicalTrials.gov, sponsor ReGenTree LLC; 2018.
Human randomised trialNCT02974907Checked 2026-09-21
Read ARISE-2, phase 3 dry-eye trial that missed both endpoints at the sourceSosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE) model. Clinical Ophthalmology, 9:877-884; 2015.
Human randomised trialPMID 26056426 · DOI 10.2147/OPTH.S80954 · NCT01387347Checked 2026-09-21
Read Phase 2 dry-eye trial: both primary endpoints missed at the sourceSosne G, Kleinman HK, Springs C, et al.. 0.1% RGN-259 (thymosin β4) ophthalmic solution promotes healing and improves comfort in neurotrophic keratopathy patients in a randomized, placebo-controlled, double-masked phase III clinical trial. International Journal of Molecular Sciences, 24(1):554; 2022.
Human randomised trialPMID 36613994 · DOI 10.3390/ijms24010554 · NCT02600429Checked 2026-09-21
Read SEER-1, terminated phase 3 trial in corneal disease at the sourceA randomized, double-blind, placebo-controlled, dose-response study of the safety and efficacy of thymosin beta 4 in the treatment of patients with epidermolysis bullosa. ClinicalTrials.gov, sponsor RegeneRx Biopharmaceuticals; 2012.
Human randomised trialNCT00311766Checked 2026-09-21
Read Terminated trial in epidermolysis bullosa at the sourceA randomized, double-blind, placebo-controlled, dose-response study of the safety and efficacy of thymosin beta 4 in the treatment of patients with venous stasis ulcers. ClinicalTrials.gov, sponsor RegeneRx Biopharmaceuticals; 2009.
Human randomised trialNCT00832091Checked 2026-09-21
Read Venous ulcer trial: no benefit over placebo at the sourceSosne G, Dunn SP, Kim C. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea, 34(5):491-496; 2015.
Human randomised trialPMID 25826322 · DOI 10.1097/ICO.0000000000000379 · NCT01393132Checked 2026-09-21
Read Small positive trial in severe dry eye at the sourceWang X, Liu L, Qi L, et al.. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. Journal of Cellular and Molecular Medicine, 25(17):8222-8228; 2021.
Human randomised trialPMID 34346165 · DOI 10.1111/jcmm.16693Checked 2026-09-21
Read First-in-human pharmacokinetics of recombinant thymosin beta-4 at the sourceRuff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Annals of the New York Academy of Sciences, 1194:223-229; 2010.
Human randomised trialPMID 20536472 · DOI 10.1111/j.1749-6632.2010.05474.xChecked 2026-09-21
Read Earlier phase 1 safety study at the sourceA phase 1/2, randomized, double-blind, placebo-controlled, sequential dose-escalation study of TB-500 (thymosin beta 4 17-23 fragment) in adults with stable atherosclerotic cardiovascular disease. ClinicalTrials.gov, sponsor Hudson Biotech; 2026.
Registered clinical trialNCT07487363Checked 2026-09-21
Read A registered study of TB-500 itself, treated with caution at the sourceBock-Marquette I, Saxena A, White MD, et al.. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature, 432(7016):466-472; 2004.
Animal studyPMID 15565145 · DOI 10.1038/nature03000Checked 2026-09-21
Read The foundational animal cardiac study at the sourceBiçer O, Adanır O, Güleryüz Y, et al.. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Joint Diseases and Related Surgery, 37(3):822-837; 2026.
Animal studyPMID 42542926 · DOI 10.52312/jdrs.2026.2951Checked 2026-09-21
Read Rat tendon study comparing TB-500 with BPC-157 at the sourceTewari K, Liu TP, Im C, et al.. Peptide Supplements and Their Therapeutic Applications in Sports Medicine. American Journal of Sports Medicine; 2026.
Systematic reviewPMID 42578445 · DOI 10.1177/03635465261464420Checked 2026-09-21
Read Systematic review of peptides in sports medicine at the source