TB-500

What Is TB-500? (And Why the Name Is Misleading)

TB-500 is one of the most misunderstood peptides on the market, and the confusion starts with the name. Here’s the critical distinction every buyer should understand:

Full Thymosin Beta-4 (Tβ4) is a naturally occurring 43-amino acid peptide (molecular weight ~4,921 Da) found in virtually all mammalian cells. It was first characterized in 1981 and is the principal G-actin sequestering peptide — a master regulator of cell structure and movement. This is the molecule used in virtually all published research.

TB-500 as sold on the grey market is typically the 7-amino-acid fragment Ac-LKKTETQ (residues 17–23 of full Tβ4), the actin-binding domain, with a molecular weight of ~847–889 Da. This has been confirmed by doping-control analysis (Esposito et al., Drug Test Anal, 2013).

To complicate matters further, some vendors sell full-length synthetic Tβ4 and call it “TB-500.” Without independent analytical testing, buyers cannot know which product they’re actually getting.

Why This Distinction Matters

The full Tβ4 molecule contains multiple functional domains that the TB-500 fragment lacks:

• Residues 1–4 (Ac-SDKP): Anti-inflammatory and anti-fibrotic properties — absent in TB-500
• Residues 1–15: Anti-apoptotic (prevents cell death) and cytoprotective — absent in TB-500
• Residues 17–23 (LKKTETQ): Actin binding, cell migration, angiogenesis — present in TB-500

When you read about Thymosin Beta-4’s impressive cardiac repair or wound healing properties, remember that those studies used a molecule with three functional domains. The TB-500 fragment contains only one of them. Extrapolating results from the whole molecule to the fragment is like testing a complete car and then claiming the steering wheel alone will get you to work.

What the Research Shows

Animal Studies (All Using Full-Length Tβ4, Not TB-500 Fragment)

Wound healing: Full Tβ4 increased re-epithelialization by 42% in rats (Malinda KM et al., J Invest Dermatol, 1999) and showed efficacy in diabetic and aged mouse models (Philp D et al., Wound Repair Regen, 2003).

Cardiac repair: The landmark study by Bock-Marquette I et al. (Nature, 2004) showed that Tβ4 enhanced myocyte survival and improved cardiac function after coronary ligation in mice. Smart N et al. (Nature, 2007) demonstrated epicardial progenitor cell mobilization. These are genuinely significant findings — in mice, using the full molecule.

Hair growth: Tβ4 activated hair follicle stem cells in rats (Philp D et al., FASEB J, 2004). Tβ4-overexpressing transgenic mice showed increased hair growth (Gao X et al., PLoS ONE, 2015).

Anti-inflammatory: Improved mortality in septic rats (Badamchian M et al., Int Immunopharmacol, 2003).

Human Clinical Data: More Than BPC-157, But Still Limited

Phase I safety: Full-length IV Tβ4 showed no serious adverse events at doses up to 1,260 mg/day for 14 days (Ruff D et al., Ann N Y Acad Sci, 2010). This is the most important human data point — it at least establishes that the full molecule can be given intravenously without acute toxicity.

Eye drops (topical Tβ4): The strongest clinical program is RGN-259 (topical Tβ4 eye drops) for neurotrophic keratopathy. Phase II data showed significant healing (Sosne G et al., Cornea, 2015). The Phase III SEER-1 trial reported complete healing in 6/10 treated eyes vs 1/8 placebo — promising but small.

Cardiac (failure): A Phase II cardiac trial (NCT00743769) completed over 15 years ago with no published results — strongly suggesting the trial failed or produced disappointing data.

PeptideIntel Evidence Assessment: No human clinical trials exist for the TB-500 fragment specifically. All human data used full-length Tβ4. The eye drop program is topical, not systemic. Claiming TB-500 fragment injections will repair hearts or heal wounds based on full Tβ4 research is scientifically unjustified.

Safety Profile

The Phase I trial of full Tβ4 is reassuring for short-term safety. However, as a growth factor modulator that promotes angiogenesis and cell migration, theoretical concerns about cancer promotion remain unstudied. No long-term safety data exists for either the full molecule or the fragment in humans. Contamination is a serious practical concern — grey-market TB-500 carries all the risks of unregulated injectable products (endotoxins, incorrect concentrations, wrong molecule).

Legal and Regulatory Status

WADA: Prohibited under S2.3 (Growth Factors and Growth Factor Modulators), explicitly listed as “Thymosin-β4 and its derivatives e.g. TB-500.” This covers both the full molecule and the fragment.

FDA: Category 2 — cannot be legally compounded. The FDA issued a warning letter to Warrior Labz SARMS (June 2023) for marketing TB-500.

Horse racing: TB-500/Tβ4 has been at the center of multiple horse doping scandals, including connections to the Tailor Made Compounding case.

Common Vendor Claims vs. Reality

What vendors say	What the evidence shows
”Promotes cardiac repair”	Full Tβ4 in mouse models; Phase II human cardiac trial never published results
”Accelerates wound healing”	Full Tβ4 in rats; TB-500 fragment never tested independently
”Clinically studied”	Phase I safety only (full Tβ4); zero clinical efficacy trials for the fragment
”Same as Thymosin Beta-4”	Usually a 7-amino-acid fragment missing 2 of 3 functional domains
”Promotes hair regrowth”	Rat studies only, using full Tβ4, not the fragment

The Bottom Line

Thymosin Beta-4 is a legitimate biological molecule with genuinely significant preclinical data, including a Nature publication on cardiac repair. But TB-500 — the product actually being sold — is typically a small fragment of that molecule, and has never been independently studied in humans. The gap between the research molecule and the commercial product is wider here than for almost any other peptide. If you’re buying TB-500 hoping for the cardiac and wound-healing benefits described in research papers, you should know that you’re likely getting a different molecule than the one that was studied.