TB-500 Evidence Guide
Direct evidence for TB-500 fragment 17-23 is preclinical. A 2026 rat tendon study was positive, but the human trials commonly cited online tested full-length thymosin beta-4, a different molecule. TB-500 should not be described as a Phase 2-validated healing peptide.
Our Take
Direct evidence for TB-500 fragment 17-23 is preclinical. A 2026 rat tendon study was positive, but the human trials commonly cited online tested full-length thymosin beta-4, a different molecule. TB-500 should not be described as a Phase 2-validated healing peptide.
- Evidence context
- Preclinical study of tendon healing and thymosin-derived repair signaling
- Evidence grade
- Level C
- Confidence
- Low
- Reference context
- Reported research reference: No validated human dose; the only current direct reference is an animal protocol
Benefits and Evidence
- Wound Healing: Level C, mostly non-human evidence - A 2026 randomized rat Achilles-tendon study found that synthetic TB-500 improved maximum load and histologic healing compared with saline. This is direct fragment-specific evidence, but it is one small animal study and does not validate human use. Human wound trials used full-length thymosin beta-4, not the TB-500 fragment.
- Cardiac Repair: Level D, mostly non-human evidence - Cardiac-repair findings come from full-length thymosin beta-4 studies, including mouse infarction models. They should not be attributed directly to the shorter TB-500 fragment, for which no convincing cardiac efficacy dataset was identified.
- Anti-Inflammation: Level D, mostly non-human evidence - Anti-inflammatory effects are well described for full-length thymosin beta-4. Whether fragment 17-23 produces a clinically meaningful anti-inflammatory effect is unknown.
- Hair Growth: Level C, mostly non-human evidence - Mouse hair-follicle findings used full-length thymosin beta-4. No direct TB-500 fragment study supports a hair-growth claim.
- Dry Eye / Corneal Healing: Level D, mostly non-human evidence - RGN-259 eye-drop studies tested full-length thymosin beta-4. They do not provide human evidence for TB-500 fragment 17-23.
Side Effects and Warnings
- No adequate human safety dataset was identified for thymosin beta-4 fragment 17-23
- FDA cites potential immunogenicity and peptide-related impurity risks for compounded TB-500
- Injection-related infection, contamination, and local-reaction risks depend on product quality and administration conditions
- Not FDA-approved for any indication
- Banned by WADA under the category of peptide hormones, growth factors, and related substances - prohibited for all competitive athletes
- Human full-length thymosin beta-4 trials do not establish safety for the shorter TB-500 fragment
- Long-term fragment-specific toxicity, immunogenicity, and carcinogenicity are unknown
Research Dosage References
- <strong>Animal research reference</strong> - 60 mcg/kg - Daily for 14 days - Dose used intraperitoneally in the 2026 rat Achilles-tendon study. It is not a validated or transferable human dose.
Mechanism of Action
TB-500 is derived from residues 17-23 of thymosin beta-4, a region associated with actin-related cell migration and tissue-repair signaling. Full-length thymosin beta-4 binds G-actin and has additional integrin-linked kinase, anti-inflammatory, angiogenic, and progenitor-cell effects. It is not established that the seven-amino-acid fragment reproduces all of those actions in humans. Direct fragment evidence currently consists mainly of laboratory and animal work, including a 2026 rat tendon-healing experiment.
Legal Status
TB-500 fragment 17-23 is not FDA-approved for any indication. FDA lists compounded thymosin beta-4 fragment among substances that may present significant safety risks because of potential immunogenicity, peptide-related impurities, and the absence of identified human exposure data. WADA prohibits thymosin beta-4 and its derivatives, including TB-500, at all times under section S2.
Primary Sources
- Thymosin beta-4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature, 2004.
- Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization. Nature, 2007.
- Thymosin beta4 promotes dermal healing. Ann N Y Acad Sci, 2007.
- Thymosin beta4 mobilizes hair follicle stem cells to undergo folliculogenesis in the mouse. FASEB J, 2004.
- Phase 2 clinical trial of thymosin beta 4 eye drops (RGN-259) for neurotrophic keratopathy. Expert Opin Investig Drugs, 2018.
- Actin-sequestering proteins and their involvement in wound healing and tissue repair. Trends Cell Biol, 2005.
- Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Jt Dis Relat Surg, 2026.
- Safety risks associated with certain bulk drug substances nominated for compounding. FDA Human Drug Compounding, 2026.
Quick Answers
Where is the strongest evidence for TB-500?
Direct evidence for TB-500 fragment 17-23 is preclinical. A 2026 rat tendon study was positive, but the human trials commonly cited online tested full-length thymosin beta-4, a different molecule. TB-500 should not be described as a Phase 2-validated healing peptide. Evidence context: Preclinical study of tendon healing and thymosin-derived repair signaling.
What are the main side effects of TB-500?
TB-500 side effects and warning signals include No adequate human safety dataset was identified for thymosin beta-4 fragment 17-23, FDA cites potential immunogenicity and peptide-related impurity risks for compounded TB-500, Injection-related infection, contamination, and local-reaction risks depend on product quality and administration conditions, Not FDA-approved for any indication, and Banned by WADA under the category of peptide hormones, growth factors, and related substances - prohibited for all competitive athletes.
What evidence level is TB-500?
TB-500 is rated Level C; the listed research status is Preclinical.