TB-500

TB-500 is a synthetic form of thymosin beta-4 (Tβ4), a 43-amino-acid, roughly 5 kDa actin-sequestering protein present in virtually all tissues except erythrocytes, with high concentrations in platelets, leukocytes, plasma, and wound fluid. Preparations are sometimes described as the active fragment of Tβ4 rather than the full sequence; in practice the two terms are used interchangeably and both promote repair, regeneration, and suppression of inflammation to a comparable degree. Tβ4 was discovered in the thymus in the 1960s by Allan Goldstein and colleagues and carries the WHO International Nonproprietary Name timbetasin.

Its central mechanism is regulation of G-actin, sequestering monomers and handing them to profilin to drive cytoskeletal reorganisation and cell migration. Because it does not bind the extracellular matrix and has a low molecular weight, it distributes systemically from any subcutaneous site. Downstream effects include VEGF-mediated angiogenesis, stem and satellite cell recruitment, collagen synthesis, and anti-inflammatory and antifibrotic signalling via its metabolite Ac-SDKP.

The systemic distribution and presumed long effective interval, relative to BPC-157, are why the traditional protocol is twice weekly rather than daily, though daily low-dose use alongside BPC-157 is also common.

Regulatory status: not approved for human use in any country; FDA Category 2 bulk drug substance (2023), which effectively removes it from compounding; WADA-prohibited under S0; banned by UFC, NFL, NCAA and other bodies. It featured in the Essendon Football Club and Cronulla-Sutherland Sharks doping cases.

Actin regulation. Tβ4 binds G-actin monomers 1:1 and prevents polymerisation, holding a mobilisable pool of monomeric actin (actin comprises about 10% of total cellular protein). On migratory signalling it hands actin to profilin; profilin opens the nucleotide-binding cleft of actin, disrupting Tβ4 binding and directing monomers to the barbed end of growing filaments. This exchange, combined with steric blocking and conformational change, produces controlled cytoskeletal reorganisation and directed migration toward damaged tissue.

Matrix-independent migration. Unlike most growth factors, Tβ4 does not bind the extracellular matrix. Its low molecular weight and lack of matrix tethering allow systemic distribution and action at distant injury sites. Keratinocyte migration is stimulated 2 to 3 fold over controls at concentrations as low as 10 picograms.

Angiogenesis. Upregulates VEGF signalling and acts directly on endothelial behaviour. The actin-binding domain at residues 17 through 23 is the principal angiogenic (and trichogenic) region.

Anti-inflammatory and antifibrotic activity. Metabolic cleavage of the N-terminal four residues yields Ac-SDKP (acetyl-seryl-aspartyl-lysyl-proline), which reduces inflammatory cytokine production, limits immune cell overactivation, and shows antifibrotic activity in animal models of lung, liver, kidney, and cardiac fibrosis. Reduced myofibroblast activity yields organised, functional repair rather than disorganised scar.

Stem and progenitor cell recruitment. Acts as a chemoattractant for stem cells, satellite cells, and myoblasts; in cardiac models it stimulates cardiomyocyte formation from epicardial precursors and activates integrin-linked kinase and the Akt survival pathway.

Functional domains and pathways. Residues 1 through 4 govern anti-inflammatory effects; 1 through 15 inhibit apoptosis; 17 through 23 trigger angiogenesis and hair growth. Implicated pathways include PI3K/Akt/eNOS, Notch, TGF-beta/Smad, and Wnt.

Wound and connective tissue: in rat models (Malinda et al., 1999) re-epithelialisation increased 42% at day 4 and 61% at day 7, contraction at least 11% greater by day 7, with increased collagen deposition and angiogenesis. Ehrlich and Hazard (2010) showed incisional wounds healing with minimal scarring, few myofibroblasts, organised mature collagen, and no loss of breaking strength. Xu et al. (2013) showed improved biomechanical properties of the femur-ligament-tibia complex, uniform fibre bundles, and increased collagen fibril diameter at 4 weeks post-surgery in rat MCL injury; adhesion and fibrous band formation reduced.

Muscle: chemoattractant for myoblasts and satellite cell-derived myocytes (Tokura et al., 2011). In dystrophin-deficient mice (Spurney et al., 2010) regenerating fibres increased significantly without improvement in strength, cardiac function, or fibrosis.

Cardiovascular: activates ILK and Akt, promotes cardiomyocyte migration and survival, stimulates epicardial precursor differentiation (Bock-Marquette et al., 2004); reduces infarct size and improves haemodynamics in rat ischaemia (Bao et al., 2013); prevents cardiomyocyte death, improves left ventricular function post-MI, and promotes cardiac wound healing.

Immune: raises leukocyte and antibody levels, inhibits leukocyte infiltration, lowers pro-inflammatory cytokines, antiviral activity, enhanced antibody–antigen binding; studied in primary immunodeficiency and autoimmune disease.

Hepatic: suppresses hepatic stellate cell activation, anti-fibrotic, stimulates regeneration via hepatocyte migration and angiogenesis, inhibits oxidative stress.

Bone: roughly 30% increase in new trabecular bone area with 47% less old cortical bone in bone models; accelerates ulcer repair.

Ocular: Phase II (Sosne and Ousler, 2015; 72 subjects) reduced dry eye discomfort 27% versus placebo with significant improvement in corneal staining and no adverse events; rapid corneal wound healing with reduced inflammatory infiltration.

Neural: in rat spinal cord injury (Cheng et al., 2014) improved all behavioural assessments, increased surviving neurons and oligodendrocytes, myelin basic protein up 57.8%, activated microglia/macrophage markers down 36.9%, IL-10 increased; improves outcome after ischaemic stroke and reduces lesion volume after TBI; studied in multiple sclerosis.

Other: suppresses pulmonary inflammation and fibrosis, protects against diabetic neuropathy, improves insulin resistance and glycaemic stability, lowers blood pressure, and drives follicles into anagen with stem cell migration to the follicle base, MMP-2 upregulation, and peri-follicular VEGF regulation.

Human pharmacodynamic timelines are limited to Phase I and Phase II work in cardiac and ophthalmic settings. In Ruff et al. (2010), escalating IV thymosin beta-4 up to 1260 mg was well tolerated with no dose-limiting toxicity; pharmacokinetics were dose-proportional with half-life increasing at higher doses. In Wang et al. (2021), 84 healthy volunteers received single or multiple IV doses of recombinant Tβ4 with mild to moderate adverse events, no dose-limiting toxicities or serious adverse events, and no accumulation on repeat dosing.

No published pharmacokinetic data exist for subcutaneous TB-500 at the doses used in practice. The frequently quoted half-life of approximately 10 days is not derived from any published study. Low molecular weight and systemic, matrix-independent distribution support less frequent dosing than short-lived peptides, but tissue half-life after subcutaneous injection in humans has not been characterised.

Anecdotal reports (not equivalent to published data): reduction in pain and inflammation within 1 to 2 weeks, particularly during loading; meaningful functional improvement in tendon and ligament injuries around weeks 3 to 4; peak effect at weeks 6 to 8. Muscle injuries respond in 2 to 4 weeks, tendon and ligament in 4 to 8 weeks, chronic lesions in 8 to 12 weeks or more with less predictable outcomes. Users report TB-500 appears more effective for systemic inflammation and larger tissue areas, while BPC-157 appears more targeted to specific sites.

An initial increase in fatigue or flu-like symptoms during the first few days is commonly reported, resolving within 24 to 48 hours and attenuating with subsequent doses; the mechanism is unclear and may reflect immune modulation. Transient head rush or light-headedness immediately post-injection subsiding within minutes, mild headache, and injection site irritation are also reported, consistent with the mild adverse event profile in Phase I trials. Incidental hair growth is occasionally noted.

No published dose-finding or pharmacokinetic study exists for subcutaneous TB-500 at practical doses; the protocols below reflect clinical practice patterns. Published human dosing comprises IV Phase I doses of 42 mg to 1260 mg, a 0.1% topical ophthalmic solution in Phase II, and a registered Phase II cardiac trial at 0.5 to 1.0 mcg/kg IV.

Reconstitution. Standard 5 mg vial with 2 mL bacteriostatic water yields 250 mcg per 10 insulin units (2.5 mg/mL). An alternative 10 mg vial with 2 mL gives 5 mg/mL, or 50 mcg per unit. Refrigerate after reconstitution.

Route and timing. Subcutaneous, typically abdomen or thigh. Systemic, matrix-independent distribution means injection site is irrelevant to efficacy, in contrast to BPC-157, whose half-life under 30 minutes favours local injection. No timing constraint and no fasting requirement, reflecting the absence of interaction with the GH axis or nutrient intake.

Traditional protocol. Loading 2 to 2.5 mg twice weekly (4 to 5 mg/week) for 4 to 6 weeks on a Monday/Thursday or Tuesday/Friday split; maintenance 2 to 2.5 mg once every 1 to 2 weeks as needed. Reported loading ranges extend to 2 to 5 mg twice weekly for 4 to 6 weeks with 2 mg maintenance every 1 to 2 weeks. An older schedule begins at 1 mg twice weekly in week 1, titrates within 1–2.5 mg twice weekly in 5–10 unit increments, and caps at 3–5 mg/week divided over 2 or 3 days, run 8 weeks on with a 4–8 week washout.

Wolverine stack. With BPC-157, daily dosing at 250 to 500 mcg of each, subcutaneous, for 4 to 8 weeks of active healing; both may be started together from day one and combined in one syringe.

By application. Acute injury: 4 to 5 mg/week for 4 to 6 weeks. Chronic injury: 4 to 5 mg/week for 6 to 8 weeks. Post-surgical: 4 to 6 mg/week for 4 to 6 weeks with surgeon approval. General maintenance: 2 to 2.5 mg every 2 weeks.

Duration. Acute protocols run 4 to 8 weeks, chronic 8 to 12 weeks. TB-500 does not suppress endogenous production or induce dependency, so mandatory cycling off has no mechanistic basis; dose reduction or cessation follows resolution of the lesion. The protocol rows below carry the low and high end of each range.

Preclinical evidence is broad; human evidence is limited to Phase I safety and Phase II cardiac and ophthalmic work.

Wound healing: Malinda et al. (1999) showed topical or intraperitoneal thymosin beta-4 in rats increased re-epithelialisation by 42% at day 4 and 61% at day 7, wound contraction at least 11% greater than controls by day 7, increased collagen deposition and angiogenesis, and keratinocyte migration stimulated 2 to 3 fold at concentrations as low as 10 picograms. Ehrlich and Hazard (2010) found incisional wounds in rats healed narrower with few myofibroblasts and organised mature collagen, without loss of breaking strength.

Ligament: Xu et al. (2013) reported improved biomechanical properties of the femur-ligament-tibia complex at 4 weeks post-surgery in a rat MCL model, with uniform fibre bundles and increased collagen fibril diameter.

Cardiac: Bock-Marquette et al. (2004) demonstrated ILK and Akt activation, cardiomyocyte migration and survival, and repair after coronary ligation in mice. Bao et al. (2013) found reduced infarct size and improved haemodynamics in a rat ischaemia model, with vessel density changes not statistically significant.

Muscle: Spurney et al. (2010) found increased regenerating fibres in dystrophin-deficient mice without improvement in strength, cardiac function, or fibrosis. Tokura et al. (2011) showed injury-induced thymosin beta-4 acts as a myoblast chemoattractant.

Neural: Cheng et al. (2014) reported improvement in all behavioural assessments after spinal cord injury in rats, myelin basic protein 57.8% above controls, and activated microglia/macrophage markers reduced by 36.9%.

Human: Ruff et al. (2010), Phase I, escalating IV doses up to 1260 mg, no dose-limiting toxicity, dose-proportional pharmacokinetics with half-life increasing at higher doses. Wang et al. (2021), Phase I in 84 healthy Chinese volunteers, single and multiple doses, no serious adverse events, no accumulation. Sosne and Ousler (2015), Phase II, 72 subjects, 27% reduction in discomfort versus placebo and significant improvement in corneal staining.

No human trials exist for musculoskeletal indications, no dose-finding or pharmacokinetic data exist for subcutaneous use, and the frequently cited half-life of approximately 10 days has no published source.