THYMOSIN BETA - 500 (TB-500)

Mechanism of Action
TB-500 is the synthetic form of an active fragment of thymosin β4, a natural 43–amino acid peptide present in most human tissues. Its primary action lies in regulation of the actin cytoskeleton: TB-500 binds to actin monomers (G-actin), preventing their excessive polymerization into filaments (F-actin). By modulating actin dynamics, it promotes cell migration, allowing cells such as fibroblasts and keratinocytes to move toward injured areas, thereby accelerating tissue repair processes.
In addition, TB-500 exerts several beneficial secondary effects: it induces angiogenesis by stimulating the formation of new blood vessels that improve perfusion of damaged tissues; it has anti-inflammatory activity, suppressing pro-inflammatory cytokines and modulating innate immune responses; and it has been reported to protect nervous tissue after neurological injury. TB-500 also interacts with growth factors, increasing the release of vascular endothelial growth factor (VEGF) and fibroblast growth factors, and enhancing collagen deposition in wounds. Overall, its mechanism is oriented toward facilitating regeneration by promoting cell migration, neovascularization, extracellular matrix repair, and inflammation modulation, creating a favorable environment for healing.
 
Known or Proposed Clinical/Therapeutic Uses
In experimental medicine, TB-500 has been evaluated mainly as a tissue repair agent. Proposed uses include accelerating healing of cutaneous wounds (especially chronic lesions such as pressure ulcers or diabetic ulcers), improving regeneration of tendons, ligaments, and skeletal muscle after trauma, and protecting cardiac muscle following myocardial infarction. For example, in preclinical cardiology studies, administration of thymosin β4 in post-infarction mice stimulated the formation of new cardiomyocytes from cardiac progenitor cells, induced their migration to damaged tissue, and promoted angiogenesis in injured myocardium. These findings suggest potential utility in post-infarction recovery and ischemic heart disease.
TB-500 has also shown usefulness in experimental ophthalmology: full-length thymosin β4 (the analogue of TB-500) accelerates healing of corneal ulcers and improves dry eye by promoting corneal re-epithelialization. Phase II clinical trials using topical thymosin β4 demonstrated accelerated healing of complicated skin ulcers, showing safety and efficacy in patients with pressure and venous ulcers.
In the sports arena, TB-500 is known for illicit use to shorten recovery times. It has been used as a doping agent in racehorses and elite athletes due to its regenerative properties, leading the World Anti-Doping Agency (WADA) to prohibit thymosin β4 in competitive sports. In summary, TB-500 is viewed as a multifunctional repair agent, with applications ranging from skin and corneal healing to cardiac and musculoskeletal recovery, although most of these uses remain under investigation and lack regulatory approval.
 
Side Effects or Associated Risks
Available data suggest that TB-500 (thymosin β4) has very low toxicity and is generally well tolerated. In a controlled clinical trial, no serious adverse effects or toxicity were observed even with very high cumulative doses (up to 1,260 mg total), indicating a wide safety margin. No significant side effects have been linked to its use in humans in published studies; reported reactions are generally limited to mild injection-site discomfort or transient headache in occasional anecdotal cases.
One debated issue has been the relationship between thymosin β4 and cancer. Some research has noted that elevated levels of thymosin β4 are associated with tumor progression in certain cancers, leading to speculation that TB-500 might be pro-carcinogenic. However, detailed studies have concluded that thymosin β4 acts as a marker or mediator in carcinogenesis rather than a direct cause. That is, its presence may correlate with tumor growth (possibly because tumors release thymosin β4 to promote angiogenesis and cell migration), but there is no evidence that administration of TB-500 induces cancer. Indeed, animal models have not shown increased tumor incidence attributable to the peptide.
Other potential risks include alterations in hormonal balance: TB-500 may increase luteinizing hormone and consequently testosterone, as well as improve insulin sensitivity, effects that could disrupt endocrine axes with prolonged, unsupervised use. Additionally, as a synthetic injectable peptide, there are risks associated with variable-quality products on the black market (contamination, inaccurate dosing). Finally, its status as a prohibited doping substance carries legal and sporting consequences if used by athletes.
Overall, documented side effects are minimal, and TB-500 has demonstrated a favorable safety profile in research to date. Nevertheless, as it is not an approved medication, use outside controlled clinical studies carries uncertainty regarding long-term effects and should be weighed carefully.