TB-500

What it is

The single most important fact about TB-500 is that no human clinical trial of the TB-500 fragment itself has ever been conducted. Any discussion of its effects has to start there. TB-500 is the common name for a synthetic peptide sold in the research-chemical marketplace as a fragment or analog of thymosin beta-4 (Tβ4), a naturally occurring 43-amino-acid protein present in nearly all human and animal cells, particularly platelets, macrophages, and epithelial tissue.

The product actually sold as "TB-500" most often corresponds to Ac-LKKTETQ, a 7-amino-acid, N-acetylated fragment (roughly 889 Da) built around the "LKKTET" actin-binding motif at positions 17–23 of the full-length Tβ4 protein.¹ This fragment is not identical to full-length thymosin beta-4, even though the two names are frequently — and incorrectly — used interchangeably in marketing and online forums.

Full-length Tβ4 was first isolated from calf thymus in the 1960s–70s and has been studied academically and by RegeneRx Biopharmaceuticals, which pursued FDA development pathways for full-length Tβ4 under the names RGN-259 (ophthalmic) and RGN-352 (injectable).³ The short fragment sold online as "TB-500" is a separate product that emerged from the veterinary and research-chemical supply chain, not from RegeneRx's clinical program. It is also known as thymosin beta-4 fragment, TB4 fragment, or Ac-LKKTETQ.

How it works

The proposed mechanism for TB-500/Tβ4 centers on regulating the cellular cytoskeleton. The LKKTET motif binds monomeric (globular) actin in roughly a 1:1 complex, preventing it from polymerizing into filamentous actin. This is theorized to lower cortical cell stiffness, making it easier for cells such as keratinocytes, fibroblasts, and endothelial cells to extend lamellipodia and migrate.¹

Through this actin-binding activity and other proposed pathways, Tβ4 has been reported in preclinical models to modulate PI3K/Akt signaling, upregulate hypoxia-inducible factor-1α (HIF-1α) and VEGF — both pro-angiogenic — and attenuate TGF-β1/SMAD signaling, a pathway linked to reduced fibrosis in animal wound models. Reported downstream effects in animal and cell studies include enhanced angiogenesis, reduced inflammation, altered immune cell migration, and faster re-epithelialization of wounds.

There is no published, peer-reviewed pharmacokinetic profile for the synthetic TB-500 fragment — no confirmed plasma half-life, maximum tolerated dose, bioavailability figure, or clearance data exist specifically for it. Full-length Tβ4 has been studied more extensively by RegeneRx in early-phase human trials, but those pharmacokinetic parameters cannot be reliably extrapolated to the shorter fragment, because truncation removes the N- and C-terminal regions that may govern the parent molecule's clearance and tissue distribution.¹ No oral bioavailability data exist either; peptides this size are typically degraded by gastrointestinal proteolysis, so virtually all non-clinical use is via subcutaneous or intramuscular injection.

What the research shows

Animal / preclinical evidence

This is where the overwhelming majority of "TB-500 works" claims originate. Rodent full-thickness dermal wound models have reported roughly 25–30% faster wound closure with full-length Tβ4 — a figure that traces to pre-2010 murine studies and is widely repeated without the caveat that it used the full protein, not the marketed fragment. Rodent Achilles tendon and ligament transection models have reported reduced inflammation and faster collagen remodeling, and cell-culture studies have shown endothelial tube formation and VEGF upregulation.

TB-500 is also widely used — and prohibited — in competitive horse racing as a purported healing aid for tendon and ligament injuries. That use is regulatory and anecdotal rather than evidentiary: racing jurisdictions treat it as prohibited largely because of unproven efficacy and detection difficulty, not because of demonstrated benefit in controlled equine trials. No dose-response curve for the synthetic fragment has been published in the 2020–2026 literature, and no formal toxicology studies — histopathology, reproductive toxicity, carcinogenicity — have been located for it.

Human evidence

The human evidence base for the TB-500 fragment itself is effectively zero. What does exist concerns full-length Tβ4, a different molecule studied by RegeneRx. Sosne and colleagues described Tβ4's potential as a corneal wound-healing and anti-inflammatory agent, supporting development of RGN-259, an ophthalmic formulation that reached Phase 3 trials.² A separate paper examined Tβ4 as a candidate for ischemic heart disease, reporting preclinical and early findings suggesting myocardial protection in animal models, with a Phase 2 proof-of-concept trial noted as still in the planning stage at time of publication.²

A UK trial on stem-cell therapy for ischemic heart failure found that higher endogenous (naturally circulating) Tβ4 plasma levels correlated with better functional outcomes — a correlational, biomarker-level finding about a patient's own Tβ4, not a trial of injected TB-500 or synthetic Tβ4 as a drug.³

Honest assessment: the gap between the fragment sold online as "TB-500" and the studied molecule (full-length Tβ4) is the single most important caveat here. Wound-healing, tendon-repair, and cardiac-protection claims for TB-500 should be treated as hypotheses extrapolated from a different molecule and from animal data — not as established human clinical findings.

Typical use and dosing

No dosing regimen for TB-500 has been established, approved, or validated in any human clinical trial. What circulates in online research and bodybuilding communities is described here purely for educational awareness — not as guidance:

These figures derive from animal mg/kg dosing scaled to human body weight by online vendors and forum authors — not from any peer-reviewed human dose-finding study. No maximum tolerated dose or therapeutic window has ever been established for humans. Some community protocols pair TB-500 with BPC-157 on the theory that the two act through complementary pathways; this combination has no controlled human safety or efficacy data of its own.

Safety, side effects, and who should avoid it

Short-duration animal efficacy studies (not formal toxicology studies) reported few overt acute toxicities at microgram doses of full-length Tβ4 in rodents, but these were not designed as safety studies and did not include organ-system histopathology. Anecdotal, uncontrolled human reports circulating in online communities mention injection-site reactions, transient lethargy, "head rush" sensations, and temporary blood pressure changes — but these come from unregulated, non-pharmacovigilance sources and can't be verified for causality, dosage accuracy, or product purity.

No reproductive toxicity or carcinogenicity data exist for the fragment, and hepatic, renal, and immune effects of sustained use are uncharacterized. Because Tβ4-related mechanisms upregulate VEGF and promote cell migration, there is a mechanism-based, unconfirmed theoretical concern that TB-500 could support neovascularization or migration of an existing tumor — this is speculative and hasn't been demonstrated in human data, but it's a reason for caution, particularly for anyone with a personal or strong family cancer history. Because Tβ4 is involved in T-cell differentiation and inflammatory regulation, prolonged exogenous dosing could theoretically affect immune tolerance, though no clinical case series has documented an infection or autoimmune event attributable to TB-500 specifically.

TB-500 is sourced almost exclusively from unregulated research-chemical vendors, so purity, sterility, and accurate labeling cannot be assumed — endotoxin contamination, incorrect peptide content, and substituted product are realistic risks tied to this supply chain, independent of the peptide's own biological profile.

Regulatory status

TB-500 is not FDA-approved for any human indication. Full-length Tβ4 — a related but different molecule — has been studied by RegeneRx Biopharmaceuticals under FDA-cleared Investigational New Drug programs for indications including dry eye/corneal healing and dermal wounds, but no Tβ4-based product, and no TB-500 fragment product, has received FDA marketing approval as of 2026.⁴

TB-500 is not currently on FDA's 503A bulk drug substances list, meaning state-licensed compounding pharmacies cannot legally compound it for patient use. It's one of several peptides — alongside BPC-157, KPV, and MOTS-c — that FDA's Pharmacy Compounding Advisory Committee (PCAC) discussed at a public meeting on July 23, 2026, evaluating whether it should be added to the list for "wound healing."⁵ As of that meeting, this is a nomination under review, not an approval; FDA has not published a final determination. Some secondary sources describe TB-500 as separately flagged as a "Category 2" bulk substance — the category the agency uses for substances with identified significant safety risks. Readers should check FDA.gov directly for the current, authoritative determination.⁴

TB-500 is sold openly online labeled "for research use only, not for human consumption" — a labeling convention vendors use to avoid FDA drug-marketing enforcement while, in practice, marketing predominantly to individual consumers for self-injection. Because these products aren't manufactured under pharmaceutical Good Manufacturing Practice standards, purity, concentration accuracy, sterility, and endotoxin levels can't be independently verified.

Thymosin-β4 and its derivatives, including TB-500 by name, are prohibited at all times, in and out of competition, under WADA's S2.3 Growth Factors category.⁶ Laboratory testing groups report LC-MS/MS assays can identify TB-500 metabolites in urine for at least 72 hours post-injection.

Frequently asked questions