TB-500

What it is

TB-500 is a short synthetic peptide fragment associated with thymosin beta-4, a naturally occurring 43-amino-acid protein involved in actin binding, cell migration, tissue repair, and inflammation-related biology^{[8 –12 ]}. FDA’s 503A materials identify the nominated substance as thymosin beta-4 fragment LKKTETQ, also known as TB-500^{[1 ]}.

TB-500 vs. full-length thymosin beta-4

The distinction between TB-500 and full-length thymosin beta-4 is central. Much of the scientific literature cited in online TB-500 marketing involves full-length thymosin beta-4, not the 7-amino-acid fragment sold online as TB-500^{[9 –12 ]}. Full-length thymosin beta-4 has been studied in topical wound and ocular formulations, while TB-500 is usually marketed as an injectable research peptide for recovery, musculoskeletal injury, or performance. Those are not interchangeable evidence bases.

FDA identifies TB-500 as “Thymosin Beta-4, Fragment (LKKTETQ),” a fragment of the full thymosin beta-4 protein^{[1 ]}. Full-length thymosin beta-4 is a 43-amino-acid actin-binding peptide with molecular formula C212H350N56O78S; TB-500 is not identical to the full protein studied in most human trials^{[8 ]}.

Mechanism

Thymosin beta-4 biology is plausible in tissue repair because the parent peptide binds G-actin and affects cellular migration, inflammation, angiogenesis, and wound remodeling^{[9 –12 ]}. However, a biologically plausible pathway does not prove that an injected fragment will reproduce the parent protein’s effects in humans. FDA states that it has not identified human exposure data for drug products containing thymosin beta-4 fragment LKKTETQ^{[6 ]}.

The peptide became prominent in athletic and grey-market settings partly because thymosin beta-4 and derivatives have been associated with tissue repair and are prohibited in sport^{[17 ]}. In public conversation, “TB-500” is often used loosely to mean thymosin beta-4, thymosin beta-4 fragments, or research-use injectable products. For editorial accuracy, ProPeptideGuide describes TB-500 as the LKKTETQ fragment and separately discusses full-length thymosin beta-4 evidence.

No FDA-approved TB-500 label exists. There is no approved indication, route, dose, contraindication list, drug-interaction section, or long-term safety database for TB-500^{[1 –6 ]}. This page describes research and regulatory status only.

Regulatory status

TB-500 is not FDA-approved for any indication. No FDA-approved finished drug product containing TB-500 or thymosin beta-4 fragment LKKTETQ was identified in FDA sources reviewed for this draft^{[1 –6 ]}.

April 2026 503A removal

Under section 503A, state-licensed pharmacies and physicians may compound using a bulk drug substance only if the substance complies with an applicable USP/NF monograph, is a component of an FDA-approved drug product if no monograph exists, or appears on FDA’s 503A bulks list^{[2 ]}. FDA’s April 22, 2026 503A update states that “Thymosin Beta-4, Fragment (LKKTETQ),” also known as TB-500, was removed from Category 2 because the nomination was withdrawn^{[1 ]}. FDA also announced that it intends to consult PCAC on July 23, 2026 regarding possible inclusion of TB-500 acetate and TB-500 free base on the 503A bulks list^{[1 ]}.

Removal from Category 2 is not FDA approval and does not itself authorize compounding. TB-500 is not listed in Category 1 in the April 22, 2026 503A document, and it was not identified on the 503A bulks list reviewed for this draft^{[1 –2 ]}. The future PCAC review means regulatory status should be rechecked after July 23, 2026^{[1 ]}.

503B and FDA safety-risk

Under section 503B, outsourcing facilities may compound from bulk drug substances only if the substance appears on FDA’s 503B bulks list or the compounded drug appears on FDA’s shortage list at the time of compounding, distribution, and dispensing^{[3 ]}. TB-500 was not identified in the FDA 503B category PDF reviewed for this draft^{[4 ]}. FDA’s safety-risk page lists thymosin beta-4 fragment LKKTETQ among withdrawn nominated substances and states that compounded drugs containing the fragment may pose immunogenicity risk due to aggregation and peptide-related impurities^{[6 ]}.

FDA further states that it has not identified human exposure data for drug products containing thymosin beta-4 fragment and lacks important safety information, including whether the drug would harm humans^{[6 ]}. This is a key distinction from full-length topical thymosin beta-4 clinical trials, which do not establish the safety of injected TB-500 fragment products^{[6 ,9 –10 ]}.

Controlled-substance and anti-doping status

TB-500 is not listed in the federal controlled-substance schedules in 21 CFR Part 1308 as reviewed for this draft^{[16 ]}. For sport, the 2026 WADA Prohibited List resource identifies peptide hormones, growth factors, related substances, and mimetics as prohibited categories, and thymosin beta-4 derivatives including TB-500 are widely treated as prohibited under WADA anti-doping rules^{[17 ]}.

Date of last regulatory verification: May 5, 2026.

Research summary

Most human research relevant to TB-500 actually studied full-length thymosin beta-4, not the TB-500 LKKTETQ fragment. This evidence can inform biological plausibility but should not be presented as direct human evidence for TB-500.

Topical wound healing — full-length thymosin beta-4

Topical wound research includes a European phase 2 study of full-length thymosin beta-4 in venous stasis ulcers. Guarnera and colleagues reported a double-blind, placebo-controlled, dose-escalation study across eight European sites that randomized 73 patients^{[9 ]}. The authors described an acceptable safety profile and suggested that a 0.03% topical thymosin beta-4 dose might accelerate wound healing in some ulcer subgroups^{[9 ]}. This was topical parent-protein research, not injected TB-500.

Dry eye — full-length thymosin beta-4

Ophthalmic research also used full-length thymosin beta-4. Sosne and Ousler conducted a randomized, double-masked, placebo-controlled phase 2 study of 0.1% thymosin beta-4 ophthalmic solution in 72 subjects with moderate to severe dry eye using a controlled adverse environment model^{[10 ]}. The study did not meet both primary endpoints at the specified visit, but several secondary endpoints improved, and no adverse events were observed^{[10 ]}. Again, this supports interest in topical thymosin beta-4, not broad claims for injected TB-500.

Preclinical cardiac literature

Preclinical cardiac literature is frequently cited in public discussion. Srivastava and colleagues reported that thymosin beta-4 promoted cardiomyocyte and endothelial migration and improved cardiac function after coronary artery ligation in mice^{[11 ]}. Later animal studies produced mixed mechanistic interpretations, including evidence that thymosin beta-4 treatment after myocardial infarction did not reprogram epicardial cells into cardiomyocytes^{[12 ]}. These studies are preclinical and cannot establish TB-500 as a cardiac repair therapy in humans.

A newer 2025 cardiovascular study reported effects of recombinant human thymosin beta-4 in mice and patients with ST-segment elevation myocardial infarction after reperfusion^{[13 ]}. That study concerns recombinant thymosin beta-4, not the grey-market TB-500 fragment. It may be relevant to the parent protein’s development but does not make TB-500 FDA-approved or clinically established.

Where the evidence ends

FDA’s safety-risk page is important for the evidence boundary: FDA states that it has not identified human exposure data for drug products containing thymosin beta-4 fragment LKKTETQ^{[6 ]}. Therefore, the human evidence base for injected TB-500 itself should be described as absent or insufficient, while full-length thymosin beta-4 has limited topical and emerging investigational data in specific clinical contexts^{[6 ,9 –10 ,13 ]}.

Overall, TB-500 should be described as a non-approved thymosin beta-4 fragment with mostly extrapolated evidence. Claims about tendon recovery, muscle repair, faster healing, anti-aging, athletic performance, or systemic regeneration are not established by human clinical trials of TB-500.

Public discourse

Sohaib Imtiaz, MD, chief medical officer at People Inc. Health Group, discussed online peptides including BPC-157, TB-500, CJC-1295, and ipamorelin as grey-market products lacking rigorous human safety data^{[18 ]}.

Adam Taylor, director of the Clinical Anatomy Learning Centre at Lancaster University, explained that some grey-market injectable peptides attempt to mimic proteins involved in tissue repair but are unapproved and lack reliable safety data^{[19 ]}.

Victoria Turnock, researcher on peptide use in the UK, discussed the demographics of experimental peptide users^{[20 ]}, while the same article summarized expert review findings that TB-500 lacks human musculoskeletal evidence.

Public discourse reflects the views of the speakers cited and does not represent medical advice or the editorial position of ProPeptideGuide.

Side effects and safety

TB-500 has no FDA-approved prescribing information, so there is no FDA-reviewed label describing contraindications, common adverse reactions, pregnancy or lactation safety, drug interactions, carcinogenicity, or long-term monitoring^{[1 –6 ]}.

Compounding-related risks

FDA’s stated compounding concerns include immunogenicity risk related to aggregation and peptide-related impurities, and absence of identified human exposure data for thymosin beta-4 fragment LKKTETQ^{[6 ]}. These concerns are particularly relevant for injectable products because sterile manufacturing, endotoxin control, identity, potency, and impurity profile are central to safety.

Topical vs. injectable safety

Full-length topical thymosin beta-4 studies reported acceptable short-term tolerability in venous ulcer and dry-eye contexts^{[9 –10 ]}. Those data should not be extrapolated to injected TB-500. A topical eye-drop study, a topical wound-gel study, and an injectable research chemical are different products, routes, exposure patterns, and safety questions.

Mechanism-based concerns

Theoretical concerns include angiogenesis and tissue-remodeling effects. Thymosin beta-4 biology includes cell migration and angiogenesis-related pathways^{[9 –12 ]}. Those mechanisms may be desirable in wound repair but could raise concerns in malignancy, abnormal vascular proliferation, pregnancy, active infection, or poorly characterized inflammatory states. Human TB-500 data are insufficient to quantify these risks.

Grey-market product quality

Grey-market products add quality risks. Products sold online as TB-500 may not contain the labeled peptide, may contain impurities, may be nonsterile, or may use ambiguous labels such as “thymosin beta-4” while actually containing a fragment. FDA’s safety-risk language should be interpreted in that context^{[6 ]}.

Available through

TB-500 is not currently available through FDA-compliant prescription or compounding channels in the United States as of 2026-05-05^{[1 –6 ]}. It is not FDA-approved, is not listed in 503A Category 1, is not on the 503A or 503B bulks lists, and awaits PCAC review scheduled for July 23, 2026^{[1 –6 ]}.

ProPeptideGuide does not link to or endorse grey-market vendors, research-chemical sellers, online peptide shops, or clinics advertising TB-500 for recovery, injury healing, anti-aging, bodybuilding, or performance use.