# Frequently Asked Questions About TB-500 > Frequently asked questions about TB-500 — safety, side effects, cancer risk, dosage, WADA status, and human clinical trials — answered from the peer-reviewed literature with citations. These are the most common questions about TB-500 that appear in search and in forum discussions about the research literature. Each answer is drawn from the peer-reviewed record and cites the specific study it references. Where the literature has no answer, that is said directly. ## What is TB-500? TB-500 is a synthetic heptapeptide (Ac-LKKTETQ) corresponding to amino acids 17–23 of Thymosin Beta-4 (Tβ4), an endogenous 43-amino-acid actin-sequestering protein. It weighs 796.9 daltons and carries the central actin-binding domain responsible for Tβ4's wound-healing and cell-migration activity [1]. It is studied primarily in rodent and equine wound-healing, angiogenesis, and tissue-repair models. It is not approved for human use. ## What does TB-500 do in the body? TB-500 is proposed to bind free G-actin monomers, regulate cell migration, promote angiogenesis via VEGFR2/VEGF signaling, and suppress NF-κB-driven inflammation [1, 15]. These effects have been observed in preclinical muscle, tendon, cardiac, and neural tissue models. No validated human mechanism data exists for the TB-500 fragment specifically. ## What are the side effects of TB-500? The most commonly reported side effect is mild injection site redness and discomfort. Transient fatigue, nausea, and dizziness have been reported anecdotally. No controlled human safety trial has characterized the side effect profile for injectable TB-500. The full-length Tβ4 protein IV Phase I study found no serious adverse events in 54 healthy volunteers [16], but that data applies to the parent protein, not this fragment. ## Is TB-500 safe to take? No human clinical trials have evaluated injectable TB-500 safety. Animal studies show a generally favorable short-term profile. The FDA classifies TB-500 as a Category 2 bulk drug substance of safety concern, prohibiting pharmaceutical compounding for humans. All injected human use exists outside a regulated clinical framework; safety for humans is undemonstrated [16, 20]. ## Does TB-500 cause cancer or promote tumor growth? TB-500 promotes angiogenesis via VEGF upregulation — the same pathway used by tumors. In mouse melanoma models, Tβ4 overexpression produced 4.3x more lung metastases and 4.4x greater tumor vascularization [12]. In human colon cancer tissue, Tβ4 stabilizes HIF-1alpha → VEGF pathway components [13]. No human study confirms or rules out cancer promotion from exogenous TB-500; researchers flag this as an unresolved concern. ## Is TB-500 banned by WADA and in competitive sports? Yes. TB-500 and Thymosin Beta-4 are prohibited by WADA under the Prohibited List category for peptide hormones, growth factors, and related substances — banned both in- and out-of-competition [18]. A Canadian athlete received a 4-year ineligibility period in connection with a non-analytical positive for combined use with another peptide. ## Are there any human clinical trials on TB-500? As of 2026, no completed Phase I/II human clinical trial on TB-500 (Ac-LKKTETQ) has been published. All published human safety data covers the full Tβ4 protein — the parent protein, not the heptapeptide fragment [16, 23]. ## What is the half-life of TB-500? No validated human half-life exists for injectable TB-500 fragment. Rat metabolite data shows primary metabolite Ac-LK peaks at 0–6 hours; Ac-LKK detectable up to 72 hours [19]. Full-length Tβ4 IV in humans has a half-life of 0.5–2.08 hours [16] — not directly applicable to the fragment. ## What is the difference between TB-500 and Thymosin Beta-4? Thymosin Beta-4 (Tβ4) is a 43-amino-acid endogenous protein. TB-500 is a synthetic 7-amino-acid fragment (positions 17–23) corresponding to the active actin-binding domain [1]. Most mechanistic and human safety literature covers the full protein; TB-500-specific studies are primarily doping-control and metabolite detection work [18, 19]. ## What is the difference between TB-500 and BPC-157? BPC-157 is a 15-amino-acid gastric-peptide fragment studied primarily in gut and tendon models via localized injection, with proposed NO-synthase mechanisms. TB-500 is a 7-amino-acid Tβ4 fragment with systemic angiogenic and cell-migration effects via G-actin sequestration and VEGF signaling. Different mechanisms, different tissue systems, different evidence bases. No peer-reviewed head-to-head study exists. ## References [1] Philp D, et al. Thymosin beta4 promotes MMP expression during wound repair. J Cell Physiol. 2006. [12] Cha HJ, et al. Role of thymosin beta4 in tumor metastasis and angiogenesis. J Natl Cancer Inst. 2003. [13] Jo JO, et al. Thymosin β4 induces VEGF via HIF-1α. Biochim Biophys Acta. 2010. [15] Qiu P, et al. Thymosin β4 inhibits TNF-α-induced NF-κB. PLoS One. 2011. [16] Wang X, et al. Phase I study of recombinant human thymosin β4. J Cell Mol Med. 2021. [18] Barton C, et al. Doping control analysis of TB-500. Drug Test Anal. 2013. [19] Rahaman KA, et al. Quantification of TB-500 and metabolites in rats. J Chromatogr B. 2024. [20] Mendias CL, Awan TM. Safety and Efficacy of Unapproved Peptide Therapies. Sports Medicine. 2026. [23] Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye. Clin Ophthalmol. 2015. --- Peer-reviewed findings on TB-500, read warmly and honestly — the evidence gaps are noted alongside the findings, and no clinic sits behind this page.