Peptides · Tissue repair (under FDA review)

TB-500 / Thymosin Beta-4

Thymosin beta-4 fragment with physician-request review.

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TB-500 / Thymosin Beta-4 molecular structure (Thymosin beta-4 peptide fragment)

Why this needs to be personal

Why Personalized TB-500 / Thymosin Beta-4

The evidence base for TB-500 is not the same as the evidence base for full-length thymosin beta-4. The marketed 17-amino-acid fragment has no large randomized clinical trial program, while the limited human exposure literature mainly involves full-length thymosin beta-4 preparations.

Physicians may submit patient-specific prescription requests for TB-500 for pharmacy review. Certain preparations may be available now when clinically appropriate, lawfully prescribed, supported by patient-specific documentation, and approved by the dispensing pharmacy. Availability is determined case by case. This is not a consumer access promise; it is a clinical, sourcing, formulation, and regulatory review process. FDA has scheduled TB-500-related bulk drug substances for discussion at the 23-24 Jul 2026 Pharmacy Compounding Advisory Committee meeting.

The regulated path is not a research vial sold to consumers. It is a physician request for a named patient, with pharmacy review of the evidence, formulation feasibility, source documentation, sterile status, and state requirements.

In brief

TB-500 / Thymosin Beta-4 Explained

TB-500 is a research peptide that is sold online and through compounding supply channels as a short fragment of a natural human protein called thymosin beta-4. Thymosin beta-4 is a small protein that every cell in the body makes; it helps cells move and supports wound healing and blood-vessel formation. TB-500 is the marketing name for a 17-amino-acid synthetic piece derived from this larger protein.

TB-500 has no FDA approval in the United States. This ingredient is part of an evolving FDA review process. Physicians may submit patient-specific prescription requests for pharmacy review. Availability is determined case by case, and availability may change after FDA review, PCAC discussion, final agency action, or state-board guidance.

Most of the published research on this peptide family is preclinical (cell and animal experiments) on the full-length thymosin beta-4 protein, not on the 17-residue fragment that is actually sold as TB-500 12. The small number of human studies that exist used intravenous full-length thymosin beta-4, not the TB-500 fragment, and that drug candidate was not advanced to FDA approval 141229.

At a glance

Quick Facts About TB-500 / Thymosin Beta-4

Category
Research peptide marketed as a synthetic thymosin beta-4 (Tβ4) fragment
Marketed identity
TB-500 is sold as an N-acetylated 17-amino-acid peptide derived from the central active region of endogenous thymosin beta-4 (43-amino-acid Tβ4); identity of supplied material from research-grade vendors is not consistently characterized
Endogenous parent peptide
Thymosin beta-4, a 43-residue, ubiquitously expressed cytosolic G-actin-sequestering protein originally isolated from calf thymus
FDA-approval status
Category 2, evolving FDA review process. Valid patient-specific prescription required; supporting clinical rationale may be requested.
FDA 503A compounding status
Physicians may submit patient-specific prescription requests for pharmacy review. Availability is determined case by case.
WADA status
Category 2, evolving FDA review process. Valid patient-specific prescription required; supporting clinical rationale may be requested.
Evidence posture
Preclinical only for the marketed TB-500 fragment. Most published human exposure data are for intravenous full-length thymosin beta-4 (phase 1, phase 2 wound healing), not for the 17-residue fragment sold as TB-500. No randomized controlled trials of the marketed TB-500 product exist.

Prescription review

Patient-Specific Prescription Only

Physicians may submit patient-specific prescription requests for TB-500 / Thymosin Beta-4 for pharmacy review. Certain preparations may be available now when clinically appropriate, lawfully prescribed, and approved by the dispensing pharmacy. Availability is determined case by case.

  • Made to order, not off a shelf. No batch sits in a warehouse waiting for buyers. Your prescription is what triggers the prep.
  • Named-patient label. The bottle carries your name. The batch records carry your prescription.
  • Dose, strength, and route chosen for you. A prescriber who knows your chart decides what gets compounded, not a manufacturer who set the strength for a trial population.
  • Licensed pharmacist on the hook. A real person, with a license that can be pulled, signs off on every prep. State inspectors check the facility.
  • Compounded drugs are not FDA-approved. They should not be evaluated using branded-drug trial data. Availability varies by state and prescribed medication.
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Real medicine, not gray market

How This Differs from a Research-Use-Only Website

A research-use-only website ships a vial from a warehouse. There is no prescription, no pharmacist, no facility inspection, and no way to recall the product if something is wrong with it. If the vial is mislabeled, contaminated, or under-potent, there is nobody whose license is at stake.

A 503A compounding pharmacy is the other thing. Your doctor writes the prescription. A licensed pharmacist, whose name is on the label, prepares the medicine in a facility the state inspects. If something goes wrong, there is a person and a license on the hook, and a documented chain of custody on every lot. That accountability is what makes it safe.

What it is

What is TB-500 / Thymosin Beta-4?

TB-500 is the trade designation under which a synthetic, N-terminally acetylated peptide is marketed by research-chemical suppliers and offered through some compounding supply channels. Vendors typically describe TB-500 as a 17-amino-acid sequence (frequently rendered Ac-LKKTETQEKNPLPSKETIEQEKQAGES or a related fragment) drawn from the central actin-binding region of endogenous thymosin beta-4 (Tβ4) 1416. Endogenous Tβ4 itself is a 43-residue, highly conserved, ubiquitously expressed cytosolic peptide first isolated from calf thymus and originally characterized as a thymic immune factor; subsequent work established its primary biochemical role as a G-actin-sequestering protein 12.

Independent identity characterization of material sold as 'TB-500' is not performed by buyers as a matter of course. Analytical chemistry literature developed for equine doping control has characterized the marketed compound by LC-MS and published detection methods for TB-500 in equine urine and plasma 18 and for TB-500 alongside six other bioactive peptides in horse plasma 22. These analytical papers are the most rigorous publicly available identity descriptions of the substance as sold in the research-peptide marketplace.

TB-500 is not bioequivalent to, and is not the same substance as, endogenous full-length thymosin beta-4. The published preclinical and limited human evidence base for thymosin beta-4 (described below) was generated with full-length recombinant or synthetic 43-residue Tβ4, not with the 17-residue fragment marketed as TB-500. Extrapolation of effects from full-length Tβ4 to the fragment is not supported by published equivalence studies.

How it works

How TB-500 / Thymosin Beta-4 Works

Class
Thymosin beta-4 peptide fragment
First studied
1980s thymosin research
Current status
Category 2, PCAC discussion scheduled 23-24 Jul 2026
Compounding category
Patient-specific 503A on physician request, pending broader FDA review

Endogenous thymosin beta-4 is the principal G-actin-sequestering peptide in mammalian cells, binding monomeric G-actin in a 1:1 stoichiometry and regulating the cellular pool of polymerization-competent actin. This actin-sequestering activity is the molecular basis for Tβ4's effects on cell motility: by modulating the balance between G-actin and F-actin, Tβ4 influences lamellipodial extension, directional migration, and the cytoskeletal remodeling required for wound closure, angiogenesis, and tissue repair 12.

Sosne and colleagues mapped the biological activities of Tβ4 to discrete short peptide sequences within the parent 43-residue protein and identified the central region as the principal contributor to wound-healing and anti-inflammatory activity in vitro and in vivo 16. This active-site mapping is the published rationale that suppliers cite for marketing the 17-residue fragment as 'TB-500.' Whether the truncated fragment recapitulates the full activity profile of intact Tβ4 in vivo is not established in published comparative data.

Downstream cellular effects of full-length Tβ4 in preclinical models include accelerated endothelial cell migration and angiogenesis 47, promotion of dermal wound closure 519, corneal epithelial healing with reduced inflammation 625, hair-follicle stem-cell mobilization and follicular neogenesis 117, and cardiac protection mediated by integrin-linked kinase signaling and adult epicardial progenitor activation 8917. A more recent mechanistic line of work positions Tβ4 as a modulator of autophagy in inflammatory contexts 26.

Research history

TB-500 / Thymosin Beta-4 Research History

Thymosin beta-4 was originally isolated from calf thymus in the 1980s and proposed as a thymic immune factor; subsequent biochemical work re-identified it as a ubiquitously expressed cytosolic G-actin-sequestering peptide rather than as a secreted immune hormone 1. The repositioning of Tβ4 from immune factor to actin-regulator drove a second wave of research focused on regenerative biology, wound healing, angiogenesis, and tissue repair, through the late 1990s and 2000s 57.

Clinical-stage development of Tβ4 was led by ReGeneRx Biopharmaceuticals through the late 2000s. A randomized phase 1 IV single- and multiple-dose study in healthy volunteers established a tolerable exposure range 12. A multicenter European phase 2 trial of topical Tβ4 in venous stasis ulcers reported dose-response wound-closure signals 13. A retrospective pre-clinical-and-clinical synthesis covering the dermal-healing data was published in 2012 19. Phase 2 ophthalmic-solution trials in dry eye disease, including a controlled-adverse-environment chamber study, reported symptom and sign improvement 2320. Cardiac-indication development was supported by the discovery work of Bock-Marquette (2004) on integrin-linked-kinase activation 8 and the epicardial-progenitor work of Smart and colleagues (2007, 2011) 917, with a clinical-development proposal published by Crockford in 2007 10; a cardioprotection proposal for congenital heart surgery was published in 2012 21. None of these programs reached FDA approval.

In parallel with the clinical-development arc for full-length Tβ4, the 17-residue 'TB-500' fragment emerged in the research-chemical and veterinary-doping spaces. Analytical chemistry literature characterized TB-500 by LC-MS 1822 in response to thoroughbred-racing doping casework, the most rigorous publicly available material on the identity and behavior of the marketed compound. The World Anti-Doping Agency added the substance class to the Prohibited List under S2 (Peptide Hormones), and equine racing authorities issued bans and detection programs in parallel 31. The FDA Pharmacy Compounding Advisory Committee evaluated thymosin beta-4 / TB-500 for the 503A bulk-drug-substances list and placed it in Category 2 (insufficient information to evaluate) 2930 4. A 2026 narrative review of unapproved peptide therapies marketed for musculoskeletal and athletic-performance indications 27 documents the persistent gap between the marketing of TB-500 and the absence of randomized clinical evidence for the fragment in humans 2.

Timeline

TB-500 / Thymosin Beta-4 Timeline

  1. 1980s Thymosin beta-4 isolated from calf thymus and initially characterized as a thymic immune factor; subsequent biochemical work re-identifies it as a ubiquitously expressed cytosolic G-actin-sequestering peptide 1
  2. 1997 Malinda et al 4. (FASEB J), thymosin beta-4 stimulates directional migration of human umbilical vein endothelial cells; first endothelial-migration mechanism paper
  3. 1999 Malinda et al 5. (J Invest Dermatol), thymosin beta-4 accelerates dermal wound healing in rodent models
  4. 2002 Sosne et al 6. (Exp Eye Res), thymosin beta-4 promotes corneal wound healing and reduces inflammation following alkali injury
  5. 2004 Philp et al 7. (Mech Ageing Dev), thymosin beta-4 promotes angiogenesis, wound healing, and hair-follicle development
  6. 2004 Bock-Marquette et al 8. (Nature), thymosin beta-4 activates integrin-linked kinase and promotes cardiac cell migration, survival, and repair after infarction
  7. 2005 Goldstein, Hannappel, Kleinman (Trends Mol Med), thymosin beta-4 repositioned from thymic immune factor to actin-sequestering protein with tissue-repair function 1
  8. 2007 Smart et al 9. (Nature), thymosin beta-4 induces adult epicardial progenitor mobilization and neovascularization
  9. 2007 Crockford (Annals NYAS), development plan published for thymosin beta-4 in ischemic heart disease at ReGeneRx 10
  10. 2007 Philp et al 11. (Annals NYAS), thymosin beta-4 induces hair growth via stem cell migration and differentiation
  11. 2010 Ruff et al 12. (Annals NYAS), randomized, placebo-controlled, single- and multiple-dose phase 1 study of intravenous full-length thymosin beta-4 in healthy volunteers establishes a tolerable IV exposure range
  12. 2010 Guarnera et al 13. (Annals NYAS), multicenter European phase 2 of topical full-length thymosin beta-4 in venous stasis ulcers reports dose-response wound-closure signals
  13. 2010 Crockford et al 14. (Annals NYAS), structure, function, and biological-property review supporting the thymosin beta-4 clinical program
  14. 2010 Philp and Kleinman (Annals NYAS), synthesis of animal studies with thymosin beta-4 as a multifunctional tissue-repair peptide 15
  15. 2010 Sosne et al 16. (FASEB J), biological activities of thymosin beta-4 mapped to discrete short peptide sequences within the parent 43-residue protein; published rationale for fragment-based agents
  16. 2011 Smart et al 17. (Nature), de novo cardiomyocyte generation from within the activated adult heart after injury, building on the epicardial-progenitor mechanism
  17. 2012 Ho et al 18. (J Chromatogr A), doping-control LC-MS analysis of TB-500 (a synthetic version of an active region of thymosin beta-4) in equine urine and plasma; among the most rigorous public identity characterizations of the marketed compound
  18. 2012 Treadwell et al 19. (Annals NYAS), synthesis of preclinical and patient data on the dermal-healing program for thymosin beta-4
  19. 2012 Sosne et al 20. (Annals NYAS), thymosin beta-4 evaluated as a dry-eye therapy; controlled-adverse-environment chamber data summarized
  20. 2012 Stromberg et al 21. (Annals NYAS), proposal to combine thymosin beta-4 and dexrazoxane for cardioprotection during congenital heart surgery
  21. 2012 Goldstein et al 2. (Expert Opin Biol Ther), thymosin beta-4 multifunctional regenerative-peptide review covering basic properties and clinical applications
  22. 2013 Kwok et al 22. (Anal Bioanal Chem), LC-MS analysis of TB-500 and six other bioactive peptides in horse plasma in the doping-control workflow
  23. 2015 Sosne and Ousler (Clin Ophthalmol), phase 2 randomized placebo-controlled trial of thymosin beta-4 ophthalmic solution for dry eye in a controlled-adverse-environment chamber design 23
  24. 2015 Bollini, Riley, Smart (Expert Opin Biol Ther), review of thymosin beta-4 functions in protection, repair, and regeneration of the mammalian heart 24
  25. 2015 Goldstein and Kleinman (Expert Opin Biol Ther), advances in the basic and clinical applications of thymosin beta-4 3
  26. 2018 Sosne (Expert Opin Biol Ther), thymosin beta-4 and the eye: bench-to-bedside narrative covering corneal healing, dry eye, and neurotrophic keratopathy 25
  27. 2018 Renga et al 26. (Expert Opin Biol Ther), thymosin beta-4 limits inflammation through autophagy, extending mechanism beyond actin sequestration
  28. 2023 FDA Pharmacy Compounding Advisory Committee evaluates thymosin beta-4 / TB-500 for the 503A bulk-drug-substances list and places it in Category 2 (insufficient information to evaluate), substance ineligible for 503A compounding pending further data 2930
  29. 2026 Mendias and Awan (Sports Med), safety and efficacy review of approved and unapproved peptide therapies (including TB-500) for musculoskeletal injuries and athletic performance; documents persistent absence of randomized clinical evidence for the marketed TB-500 fragment in humans 27
  30. 2026 Di et al 28. (Peptides), review positioning thymosin beta-4 as an emerging therapeutic candidate for kidney diseases (preclinical)

Natural role

Biological Role of TB-500 / Thymosin Beta-4

Endogenous thymosin beta-4 is one of the most abundant cytosolic peptides in mammalian cells 9628. Its primary biochemical function is sequestration of monomeric G-actin in a 1:1 complex, which regulates the cellular pool of polymerization-competent actin and consequently the rate and direction of actin-filament assembly required for cell motility and morphogenesis 12 11.

In the regenerative-biology literature, Tβ4 has been implicated in coordinating cell migration, angiogenesis, anti-apoptotic signaling, and reduction of inflammation following tissue injury, a phenotype that has been observed across cardiac, dermal, corneal, hair-follicle, and renal tissue models 7817. The biological role of the truncated 17-residue TB-500 fragment, independent of full-length Tβ4, is less well characterized.

Clinical contexts studied

Clinical Contexts for TB-500 / Thymosin Beta-4

Marketing-claimed: musculoskeletal injury recovery and athletic performance enhancement preclinical

Common consumer-facing marketing claim for TB-500. Not supported by randomized clinical trials of the marketed 17-residue fragment in humans. WADA-prohibited at all times.

Online supplier and athletic-performance marketing positions TB-500 as a soft-tissue and tendon-healing peptide. A 2026 narrative review of unapproved peptide therapies for musculoskeletal injury and athletic performance 27 documents that no randomized clinical trial evidence supports the marketing claims for the 17-residue TB-500 fragment in humans. The preclinical evidence base 5719 was generated with full-length thymosin beta-4, not with the marketed fragment, and animal-to-human extrapolation is not validated. WADA prohibits the substance class at all times 31; equine racing authorities ban its use and detect it in casework 1822.

Dermal wound healing (full-length Tβ4 preclinical and limited human signal) preclinical

Preclinical wound-healing evidence is for full-length thymosin beta-4, not for the marketed TB-500 fragment. Phase 2 venous-stasis-ulcer data exist for topical full-length Tβ4 and were not advanced to FDA approval.

Animal-model wound-healing data for full-length Tβ4 include rodent dermal wound closure 5, angiogenesis and hair-follicle responses 7, and a clinical-translation synthesis 19. Human-stage data from ReGeneRx include a phase 1 IV safety trial 12 and a multicenter European phase 2 of topical Tβ4 in venous stasis ulcers reporting dose-response wound-closure signals 13. The program did not reach FDA approval. None of this work used the 17-residue TB-500 fragment.

Corneal and ocular surface repair (full-length Tβ4 preclinical and phase 2) preclinical

Preclinical and phase 2 ophthalmic data are for full-length Tβ4 ophthalmic solution, not for the marketed TB-500 fragment.

Sosne and colleagues characterized full-length Tβ4 as a corneal wound-healing and anti-inflammatory peptide in rodent alkali-injury models 6 and reviewed the bench-to-bedside arc through corneal, dry-eye, and neurotrophic-keratopathy applications 25. A phase 2 randomized placebo-controlled trial of full-length Tβ4 ophthalmic solution in dry eye disease using a controlled-adverse-environment chamber design 2320 reported symptom and sign improvement. The program did not reach FDA approval. No ophthalmic clinical data exist for the marketed TB-500 fragment.

Cardiac repair after ischemic injury (full-length Tβ4 preclinical) preclinical

Preclinical cardiac-repair signal is for full-length Tβ4. No completed cardiac human program; the ReGeneRx development plan was published as a proposal and did not progress to approval.

Bock-Marquette et al. (Nature 2004) demonstrated that exogenous Tβ4 activates integrin-linked kinase and promotes cardiac-cell migration, survival, and post-infarction repair 8. Smart and colleagues described thymosin-beta-4-induced mobilization of adult epicardial progenitor cells and de novo cardiomyocyte generation from activated adult heart 917. Reviews 24 summarized cardiac-repair mechanism candidates. The clinical-development proposal for ischemic heart disease 10 and a pediatric cardiac-surgery cardioprotection proposal 21 were published but no completed phase 3 program followed.

Compounded use

Compounded TB-500 / Thymosin Beta-4 (503A)

Physicians may submit patient-specific prescription requests for pharmacy review. For TB-500, certain preparations may be available now when clinically appropriate, lawfully prescribed, and approved by the dispensing pharmacy. Availability is determined case by case and may depend on patient-specific documentation, ingredient status, source qualification, formulation feasibility, state requirements, and pharmacist judgment. The review starts with the evidence constraint: The evidence base for TB-500 is not the same as the evidence base for full-length thymosin beta-4. The marketed 17-amino-acid fragment has no large randomized clinical trial program, while the limited human exposure literature mainly involves full-length thymosin beta-4 preparations.

This ingredient is part of an evolving FDA review process. RonanRx is monitoring FDA's PCAC process and any subsequent agency action. FDA has scheduled TB-500-related bulk drug substances for discussion at the 23-24 Jul 2026 Pharmacy Compounding Advisory Committee meeting. Availability may change after FDA review, PCAC discussion, final agency action, or state-board guidance. For TB-500, RonanRx ties that monitoring to the evidence limits described above and to any patient-specific documentation submitted by the prescriber.

Valid patient-specific prescription required. Supporting clinical rationale may be requested. Compounded medications are not FDA-approved. No consumer self-ordering, no office stock, no bulk dispensing. Requests for TB-500 are reviewed before any preparation is made or released. The regulated path is not a research vial sold to consumers. It is a physician request for a named patient, with pharmacy review of the evidence, formulation feasibility, source documentation, sterile status, and state requirements.

Formulations and routes

TB-500 / Thymosin Beta-4 Formulations and Routes

FormConcentrationDescription
Research-grade lyophilized peptide (not for human administration) — Material sold as 'TB-500' in the research-chemical marketplace is typically supplied as lyophilized powder from non-pharmaceutical vendors, reconstituted in bacteriostatic water by the end user. Identity, purity, and sterility are not subject to USP <797> sterile compounding standards; analytical characterization of marketed material has been performed by equine doping-control laboratories rather than by pharmaceutical-grade release testing.1822

Routes used in published literature: subcutaneous, intramuscular, intravenous.

Dosing

TB-500 / Thymosin Beta-4 Dosing

RonanRx does not publish a consumer dosing schedule for TB-500. Any request requires a valid patient-specific prescription, supporting clinical rationale, and pharmacist review. Route, strength, dosing interval, monitoring expectations, and dispensing quantity would be determined case by case from the prescriber's documentation and pharmacy feasibility review.

Consumer-facing internet sources publish suggested injection schedules (typically described as weekly subcutaneous or intramuscular dosing for several weeks). These schedules are not derived from published clinical data, are not subject to pharmacovigilance, and are not endorsed by RonanRx. Prescribers asked about TB-500 are referred to the FDA Category 2 designation 2930 and to the practice-facing safety review 27.

Doses listed are literature context, not patient instructions. Dosing decisions are made by the prescribing doctor and tailored to the individual patient.

Safety

TB-500 / Thymosin Beta-4 Safety

Safety overview

Human safety data are limited and do not pertain to the marketed 17-residue TB-500 fragment. A randomized phase 1 single- and multiple-dose IV study of full-length thymosin beta-4 in healthy volunteers 12 established a tolerable IV exposure range with no severe drug-related adverse events at the doses tested. A multicenter European phase 2 topical Tβ4 trial in venous stasis ulcers 13 reported no unexpected safety signals at the topical doses studied. A phase 2 ophthalmic-solution dry-eye trial 23 reported acceptable tolerability for ocular administration of full-length Tβ4. None of these data characterize the safety of subcutaneously or intramuscularly injected research-grade TB-500 from non-pharmaceutical suppliers.

Material marketed as TB-500 is research-grade peptide; impurity profile, endotoxin content, sterility, and identity verification are not subject to pharmaceutical-grade quality control in the consumer supply chain. Practice-facing reviews of unapproved peptide therapies 27 catalog reports of injection-site reactions, sterility-related events, and adulteration or mis-identification of supplied material as the most concrete safety considerations for the consumer marketplace. Theoretical concerns include immunogenicity to a non-physiologic peptide fragment and unintended effects of chronic cytoskeletal modulation; published data do not characterize these risks for chronic dosing in humans.

TB-500 is prohibited at all times under WADA S2 31 and is the subject of equine doping detection programs 1822. Athletes, racehorse trainers, and any individual subject to anti-doping testing should be aware that exposure produces detectable findings.

Contraindications

Honest gap. No FDA-approved product exists for TB-500 or full-length thymosin beta-4; no labeled contraindications are published. Physicians may submit patient-specific prescription requests for pharmacy review. Availability is determined case by case.

Searched: PubMed, FDA Drugs@FDA, DailyMed on 2026-05-11 · terms TB-500 contraindications; thymosin beta-4 contraindications; thymosin beta-4 prescribing information.

Drug interactions

Honest gap. No FDA-approved labeling and no published clinical drug-interaction data for TB-500 or full-length thymosin beta-4. Thymosin beta-4 is a peptide cleared by proteolytic catabolism; cytochrome P450-mediated interactions are not anticipated mechanistically but no human DDI studies are published.

Searched: PubMed, FDA Drugs@FDA, DailyMed on 2026-05-11 · terms TB-500 drug interactions; thymosin beta-4 drug interactions; thymosin beta-4 cytochrome.

Adverse events

Published adverse-event data pertain to full-length thymosin beta-4 from ReGeneRx clinical trials, not to the marketed TB-500 fragment. In the phase 1 IV single- and multiple-dose study in healthy volunteers 12, the most commonly reported events were mild and not consistently attributable to study drug. In the multicenter European phase 2 venous-stasis-ulcer trial of topical full-length Tβ4 13, the topical formulation was reported as well tolerated at the doses studied. The phase 2 dry-eye ophthalmic-solution trial 2320 reported tolerability consistent with topical ocular use of a peptide solution.

For research-grade material marketed as TB-500 and self-administered by injection, no systematic adverse-event reporting framework exists. Practice-facing reviews 27 catalog injection-site reactions, sterility-related events, dosing errors, and identity/adulteration concerns as the principal real-world safety considerations and emphasize the absence of pharmacovigilance infrastructure for the consumer supply chain.

Monitoring

Monitoring TB-500 / Thymosin Beta-4 Therapy

No RonanRx-specific monitoring protocol has been established for TB-500. If a patient-specific prescription is submitted, supporting clinical rationale may be requested, and monitoring expectations would be reviewed case by case against the published evidence, route, sterile or nonsterile status, concomitant therapies, and patient risk factors.

Special populations

TB-500 / Thymosin Beta-4 in Special Populations

Pregnancy

No FDA-recognized use guidance for TB-500 in this population is established. Any patient-specific request would require prescriber rationale, patient-specific risk review, and pharmacist approval before dispensing.

Lactation

No FDA-recognized use guidance for TB-500 in this population is established. Any patient-specific request would require prescriber rationale, patient-specific risk review, and pharmacist approval before dispensing.

Pediatric

No FDA-recognized use guidance for TB-500 in this population is established. Any patient-specific request would require prescriber rationale, patient-specific risk review, and pharmacist approval before dispensing.

Evidence quality

TB-500 / Thymosin Beta-4 Evidence Quality

Evidence supporting any human use of the marketed 17-residue TB-500 fragment is absent. No randomized clinical trial of TB-500 in humans has been published, and the analytical chemistry literature that does describe the marketed substance was developed for equine doping control rather than for therapeutic claims 1822. A practice-facing 2026 review of unapproved peptide therapies marketed for musculoskeletal injury and athletic performance 27 confirms the persistent gap between marketing claims for TB-500 and the absence of human randomized clinical evidence for the fragment.

Evidence supporting the related but distinct full-length thymosin beta-4 peptide is mostly preclinical. Core mechanism work, G-actin sequestration 12, endothelial migration and angiogenesis 47, dermal wound healing 519, corneal repair 625, hair-follicle effects 117, cardiac repair via ILK and epicardial progenitors 8917, and inflammation/autophagy 26, is supported by animal-model and cell-culture data. The small set of human studies of full-length Tβ4, phase 1 IV 12, phase 2 topical venous ulcer 13, phase 2 ophthalmic solution 2320, did not progress to FDA approval, and the development sponsor's program is no longer active. Independent active-region mapping 16 established the rationale for fragment-based agents but did not validate the marketed 17-residue TB-500 sequence as therapeutically equivalent to full-length Tβ4 in humans.

The FDA Pharmacy Compounding Advisory Committee placed thymosin beta-4 / TB-500 in Category 2 (insufficient information to evaluate) on the 503A bulk drug substances list 2930; Category 2 substances are part of an evolving FDA review process for 503A compounding. WADA prohibits the substance class at all times under S2 31.

Major studies

Major TB-500 / Thymosin Beta-4 Clinical Studies

StudyDesignParticipantsDurationFinding
Ruff et al. (2010, Annals NYAS), Phase 1 IV full-length Tβ4 Randomized, placebo-controlled, single- and multiple-dose phase 1 study of intravenous full-length thymosin beta-4 in healthy volunteers — Single- and multiple-dose, short-term Established a tolerable IV exposure range for full-length Tβ4 with no severe drug-related adverse events at the doses tested; not a study of the marketed 17-residue TB-500 fragment 12
Guarnera et al. (2010, Annals NYAS), Phase 2 topical Tβ4 in venous ulcers Multicenter European phase 2 randomized trial of topical full-length thymosin beta-4 in patients with venous stasis ulcers — Per-protocol topical dosing schedule Dose-response wound-closure signals reported for topical full-length Tβ4; program did not advance to FDA approval; not a study of the marketed 17-residue TB-500 fragment 13
Sosne and Ousler (2015, Clin Ophthalmol), Phase 2 Tβ4 ophthalmic for dry eye Randomized placebo-controlled phase 2 trial of full-length thymosin beta-4 ophthalmic solution in dry eye disease using a controlled-adverse-environment chamber design — — Symptom and sign improvement reported for full-length Tβ4 ophthalmic solution; program did not advance to FDA approval 23
Bock-Marquette et al. (2004, Nature), Cardiac repair via ILK Preclinical mechanistic study in rodent myocardial-infarction models — — Exogenous thymosin beta-4 activates integrin-linked kinase, promotes cardiac-cell migration and survival, and improves post-infarction cardiac function 8
Smart et al. (2007, Nature), Epicardial progenitor activation Preclinical mechanistic study of adult epicardial progenitor cells in murine cardiac injury — — Thymosin beta-4 induces adult epicardial progenitor mobilization and neovascularization 9
Smart et al. (2011, Nature), De novo cardiomyocytes Preclinical lineage-tracing study in adult murine heart following injury and Tβ4 priming — — De novo cardiomyocyte generation from within the activated adult heart after injury 17
Malinda et al. (1999, J Invest Dermatol), Dermal wound healing Rodent full-thickness dermal wound model with topical or systemic full-length Tβ4 — — Thymosin beta-4 accelerates wound closure relative to vehicle; angiogenesis and re-epithelialization improved 5
Sosne et al. (2002, Exp Eye Res), Corneal alkali injury Murine corneal alkali-injury model with topical full-length Tβ4 — — Promotes corneal wound healing and reduces inflammation in vivo following alkali burn 6
Malinda et al. (1997, FASEB J), Endothelial migration In vitro HUVEC chemotaxis assay with synthetic Tβ4 — — Thymosin beta-4 stimulates directional migration of human umbilical vein endothelial cells; mechanistic basis for angiogenesis effects 4
Philp et al. (2004, Mech Ageing Dev), Angiogenesis and hair follicle Preclinical in vivo and ex vivo studies of full-length Tβ4 in angiogenesis, wound healing, and hair-follicle assays — — Thymosin beta-4 promotes angiogenesis, wound healing, and hair-follicle development in rodent models 7
Philp et al. (2007, Annals NYAS), Hair growth via stem cells Rodent hair-growth model with topical and intradermal full-length Tβ4 — — Thymosin beta-4 induces hair growth via stem-cell migration and differentiation in murine skin 11
Sosne et al. (2010, FASEB J), Active-site mapping Synthetic short-peptide screening across the parent 43-residue Tβ4 sequence in wound-healing and migration assays — — Biological activities of Tβ4 are localized to discrete short sequences in the central region of the parent peptide; rationale for fragment-based agents (cited by suppliers of marketed TB-500) 16
Ho et al. (2012, J Chromatogr A), TB-500 doping LC-MS Analytical chemistry development of LC-MS detection for TB-500 in equine urine and plasma — — Among the most rigorous publicly available identity characterizations of the marketed 'TB-500' substance; established detection windows and reference spectra used in equine doping control 18
Kwok et al. (2013, Anal Bioanal Chem), Seven peptides in horse plasma Multiplexed LC-MS detection of seven bioactive peptides including TB-500 in horse plasma — — Detection method development supporting equine racing doping-control program 22
Renga et al. (2018, Expert Opin Biol Ther), Tβ4 and autophagy Preclinical mechanistic review and primary data on autophagy regulation by thymosin beta-4 — — Thymosin beta-4 limits inflammation through autophagy modulation; extends mechanism beyond actin sequestration 26
Mendias and Awan (2026, Sports Med), Unapproved peptide review Narrative review of safety and efficacy of approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance — — Documents persistent absence of randomized clinical evidence for the marketed TB-500 fragment in humans and catalogs supply-chain quality concerns in the consumer peptide marketplace 27

Pharmacology

TB-500 / Thymosin Beta-4 Pharmacokinetics & Pharmacodynamics

Pharmacokinetics

Pharmacokinetic data are limited to the phase 1 IV single- and multiple-dose study of full-length thymosin beta-4 in healthy volunteers 12. As a peptide, thymosin beta-4 is expected to be cleared by proteolytic catabolism; cytochrome P450-mediated metabolism is not anticipated. No human PK data are published for subcutaneously or intramuscularly administered TB-500 fragment material from research-grade suppliers.

RonanRx operations

TB-500 / Thymosin Beta-4 Compounding & Operations

503A compounding

Physicians may submit patient-specific prescription requests for pharmacy review. For TB-500, certain preparations may be available now when clinically appropriate, lawfully prescribed, and approved by the dispensing pharmacy. Availability is determined case by case and may depend on patient-specific documentation, ingredient status, source qualification, formulation feasibility, state requirements, and pharmacist judgment. The review starts with the evidence constraint: The evidence base for TB-500 is not the same as the evidence base for full-length thymosin beta-4. The marketed 17-amino-acid fragment has no large randomized clinical trial program, while the limited human exposure literature mainly involves full-length thymosin beta-4 preparations.

This ingredient is part of an evolving FDA review process. RonanRx is monitoring FDA's PCAC process and any subsequent agency action. FDA has scheduled TB-500-related bulk drug substances for discussion at the 23-24 Jul 2026 Pharmacy Compounding Advisory Committee meeting. Availability may change after FDA review, PCAC discussion, final agency action, or state-board guidance. For TB-500, RonanRx ties that monitoring to the evidence limits described above and to any patient-specific documentation submitted by the prescriber.

Valid patient-specific prescription required. Supporting clinical rationale may be requested. Compounded medications are not FDA-approved. No consumer self-ordering, no office stock, no bulk dispensing. Requests for TB-500 are reviewed before any preparation is made or released. The regulated path is not a research vial sold to consumers. It is a physician request for a named patient, with pharmacy review of the evidence, formulation feasibility, source documentation, sterile status, and state requirements.

Pharmacist review

For TB-500, the pharmacist review starts before any preparation is made. Valid patient-specific prescription required. Supporting clinical rationale may be requested. The pharmacist reviews ingredient status, sourcing, formulation feasibility, state requirements, patient-specific documentation, and whether dispensing is appropriate case by case.

Quality and traceability

If a TB-500 preparation is approved after pharmacy review, RonanRx applies source documentation, formulation records, lot traceability, release checks, and storage controls appropriate to the actual dosage form. Research-use vial storage practices do not substitute for pharmacy-assigned storage, beyond-use dating, sterility controls when applicable, or recallable batch records. The patient-specific framework and quality controls are documented in the cited compounding references 323433.

FAQ

Frequently Asked Questions About TB-500 / Thymosin Beta-4

Can physicians request TB-500 through RonanRx?

Physicians may submit patient-specific prescription requests for pharmacy review. Certain preparations may be available now when clinically appropriate, lawfully prescribed, and approved by the dispensing pharmacy. Availability is determined case by case. Compounded medications are not FDA-approved, and no consumer self-ordering, office stock, or bulk dispensing is offered.2930

Why do I see TB-500 sold online by 'research peptide' vendors?

Material marketed as TB-500 in the consumer and athletic-performance marketplace is research-grade peptide from non-pharmaceutical suppliers and is sold without FDA approval, pharmaceutical-grade release testing, or pharmacovigilance 27. The most rigorous public identity characterizations of the marketed substance were developed by equine doping-control laboratories rather than by pharmaceutical-quality release testing 18. RonanRx is not part of that supply chain 22.

Is TB-500 the same thing as thymosin beta-4?

No. Endogenous thymosin beta-4 (Tβ4) is a 43-amino-acid peptide naturally expressed in every cell 14. TB-500 is the marketing designation for a synthetic 17-amino-acid peptide derived from the central active region of Tβ4 16. The published preclinical and limited human evidence base is overwhelmingly for the full-length 43-residue protein, not for the 17-residue marketed fragment 1. Equivalence of the fragment to the full-length peptide in humans is not established.

Are there human clinical trials of TB-500?

No published randomized clinical trial of the marketed 17-residue TB-500 fragment in humans is available. The small number of human studies in the thymosin beta-4 literature used full-length intravenous or topical thymosin beta-4 (from the ReGeneRx development program) and did not advance to FDA approval 1213. A 2026 review of unapproved peptide therapies for musculoskeletal injury and athletic performance documents the persistent absence of randomized clinical evidence for the marketed fragment 2327.

Is TB-500 banned in sport?

Yes. TB-500 is prohibited at all times under the World Anti-Doping Agency Prohibited List S2 class (Peptide Hormones, Growth Factors, Related Substances and Mimetics) 31. LC-MS detection methods for TB-500 in equine and human matrices are published and in use by anti-doping laboratories 1822.

Clinician resource

Download the TB-500 / Thymosin Beta-4 Clinical Monograph (PDF)

The full white paper covers every section on this page plus chemical identity, evidence grading, indication-by-indication summaries, research gaps, and reference appendix. Suitable for sharing with prescribing doctors and pharmacist reviewers.

Download information packet ↓

References

References

  1. [goldstein2005] Goldstein AL, Hannappel E, Kleinman HK. Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues. Trends in Molecular Medicine. 2005. PMID 16099219. (accessed 2026-05-11)
  2. [goldstein2012_review] Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opinion on Biological Therapy. 2012. PMID 22074294. (accessed 2026-05-11)
  3. [goldstein2015_advances] Goldstein AL, Kleinman HK. Advances in the basic and clinical applications of thymosin β4. Expert Opinion on Biological Therapy. 2015. PMID 26096726. (accessed 2026-05-11)
  4. [malinda1997_huvec] Malinda KM, Goldstein AL, Kleinman HK. Thymosin beta 4 stimulates directional migration of human umbilical vein endothelial cells. FASEB Journal. 1997. PMID 9194528. (accessed 2026-05-11)
  5. [malinda1999_wound] Malinda KM, Sidhu GS, Mani H, Banaudha K, Maheshwari RK, Goldstein AL, Kleinman HK. Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology. 1999. PMID 10469335. (accessed 2026-05-11)
  6. [sosne2002_cornea] Sosne G, Szliter EA, Barrett R, Kernacki KA, Kleinman H, Hazlett LD. Thymosin beta 4 promotes corneal wound healing and decreases inflammation in vivo following alkali injury. Experimental Eye Research. 2002. PMID 11950239. (accessed 2026-05-11)
  7. [philp2004_angiogenesis] Philp D, Goldstein AL, Kleinman HK. Thymosin beta4 promotes angiogenesis, wound healing, and hair follicle development. Mechanisms of Ageing and Development. 2004. PMID 15037013. (accessed 2026-05-11)
  8. [bock_marquette2004] Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004. PMID 15565145. (accessed 2026-05-11)
  9. [smart2007_epicardium] Smart N, Risebro CA, Melville AA, Moses K, Schwartz RJ, Chien KR, Riley PR. Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization. Nature. 2007. PMID 17108969. (accessed 2026-05-11)
  10. [crockford2007_cardiac_dev] Crockford D. Development of thymosin beta4 for treatment of patients with ischemic heart disease. Annals of the New York Academy of Sciences. 2007. PMID 17947592. (accessed 2026-05-11)
  11. [philp2007_hair] Philp D, St-Surin S, Cha HJ, Moon HS, Kleinman HK, Elkin M. Thymosin beta 4 induces hair growth via stem cell migration and differentiation. Annals of the New York Academy of Sciences. 2007. PMID 17947589. (accessed 2026-05-11)
  12. [ruff2010_phase1] Ruff 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. 2010. PMID 20536472. (accessed 2026-05-11)
  13. [guarnera2010_venous] Guarnera G, DeRosa A, Camerini R. The effect of thymosin treatment of venous ulcers. Annals of the New York Academy of Sciences. 2010. PMID 20536470. (accessed 2026-05-11)
  14. [crockford2010_structure] Crockford D, Turjman N, Allan C, Angel J. Thymosin beta4: structure, function, and biological properties supporting current and future clinical applications. Annals of the New York Academy of Sciences. 2010. PMID 20536467. (accessed 2026-05-11)
  15. [philp2010_animal_studies] Philp D, Kleinman HK. Animal studies with thymosin beta, a multifunctional tissue repair and regeneration peptide. Annals of the New York Academy of Sciences. 2010. PMID 20536453. (accessed 2026-05-11)
  16. [sosne2010_active_sites] Sosne G, Qiu P, Goldstein AL, Wheater M. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB Journal. 2010. PMID 20179146. (accessed 2026-05-11)
  17. [smart2011_denovo_cardiomyocytes] Smart N, Bollini S, Dubé KN, Vieira JM, Zhou B, Davidson S, Yellon D, Riegler J, Price AN, Lythgoe MF, Pu WT, Riley PR. De novo cardiomyocytes from within the activated adult heart after injury. Nature. 2011. PMID 21654746. (accessed 2026-05-11)
  18. [ho2012_tb500] Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of Chromatography A. 2012. PMID 23084823. (accessed 2026-05-11)
  19. [treadwell2012_dermal] Treadwell T, Kleinman HK, Crockford D, Hardy MA, Guarnera GT, Goldstein AL. The regenerative peptide thymosin β4 accelerates the rate of dermal healing in preclinical animal models and in patients. Annals of the New York Academy of Sciences. 2012. PMID 23050815. (accessed 2026-05-11)
  20. [sosne2012_dryeye] Sosne G, Qiu P, Ousler GW 3rd, Dunn SP, Crockford D. Thymosin β4: a potential novel dry eye therapy. Annals of the New York Academy of Sciences. 2012. PMID 23050816. (accessed 2026-05-11)
  21. [stromberg2012_cardiac_surgery] Stromberg D, Raymond T, Samuel D, Crockford D, Stromberg M, Chang AC. Use of the cardioprotectants thymosin β4 and dexrazoxane during congenital heart surgery: proposal for a randomized, double-blind, clinical trial. Annals of the New York Academy of Sciences. 2012. PMID 23050818. (accessed 2026-05-11)
  22. [kwok2013_horse_peptides] Kwok WH, Ho EN, Lau MY, Leung GN, Wong AS, Wan TS. Doping control analysis of seven bioactive peptides in horse plasma by liquid chromatography-mass spectrometry. Analytical and Bioanalytical Chemistry. 2013. PMID 23318763. (accessed 2026-05-11)
  23. [sosne2015_dryeye_p2] Sosne 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. 2015. PMID 26056426. (accessed 2026-05-11)
  24. [bollini2015_cardiac_review] Bollini S, Riley PR, Smart N. Thymosin β4: multiple functions in protection, repair and regeneration of the mammalian heart. Expert Opinion on Biological Therapy. 2015. PMID 26094634. (accessed 2026-05-11)
  25. [sosne2018_eye_review] Sosne G. Thymosin beta 4 and the eye: the journey from bench to bedside. Expert Opinion on Biological Therapy. 2018. PMID 30063853. (accessed 2026-05-11)
  26. [renga2018_autophagy] Renga G, Oikonomou V, Stincardini C, Pariano M, Borghi M, Costantini C, Bartoli A, Garaci E, Goldstein AL, Romani L. Thymosin β4 limits inflammation through autophagy. Expert Opinion on Biological Therapy. 2018. PMID 30063848. (accessed 2026-05-11)
  27. [mendias2026] Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Medicine. 2026. PMID 41966639. (accessed 2026-05-11)
  28. [di2026_kidney] Di H, Huang J, Zhang D, Ni F. Thymosin beta 4: An emerging therapeutic candidate for kidney diseases. Peptides. 2026. PMID 41570941. (accessed 2026-05-11)
  29. [fda_503a_bulk_substances] U.S. Food and Drug Administration. Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act — Interim Policy, Category 1 and Category 2 lists. FDA Drug Compounding. 2024. https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act (accessed 2026-05-11)
  30. [fda_pcac] U.S. Food and Drug Administration. Pharmacy Compounding Advisory Committee — meeting materials, including evaluation of thymosin beta-4 / TB-500 for the 503A bulk drug substances list. FDA Advisory Committees. 2023. https://www.fda.gov/advisory-committees/human-drug-advisory-committees/pharmacy-compounding-advisory-committee (accessed 2026-05-11)
  31. [wada_list] World Anti-Doping Agency. The Prohibited List — World Anti-Doping Agency (Section S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics). WADA Prohibited List. 2025. https://www.wada-ama.org/en/prohibited-list (accessed 2026-05-11)
  32. [fda503a] U.S. Food and Drug Administration. Compounding Laws and Policies — Section 503A of the Federal Food, Drug, and Cosmetic Act. FDA Drug Compounding. 2024. https://www.fda.gov/drugs/human-drug-compounding/compounding-laws-and-policies (accessed 2026-05-11)
  33. [usp_797] United States Pharmacopeia. USP General Chapter <797> Pharmaceutical Compounding — Sterile Preparations. USP Compounding Compendium. 2023. https://www.usp.org/compounding/general-chapter-797 (accessed 2026-05-11)
  34. [usp_795] United States Pharmacopeia. USP General Chapter <795> Pharmaceutical Compounding — Nonsterile Preparations. USP Compounding Compendium. 2023. https://www.usp.org/compounding/general-chapter-795 (accessed 2026-05-11)

How to access

How to Access TB-500 / Thymosin Beta-4

Physicians may submit patient-specific prescription requests for TB-500 / Thymosin Beta-4 for pharmacy review. Availability is determined case by case, and RonanRx is monitoring FDA's PCAC process and any subsequent agency action.

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Patient without a doctor

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