# TB-500 FAQ: Steroid Question, Side Effects, the BPC-157 Comparison, and Legality

> TB-500 FAQ: is TB-500 a steroid, what are the side effects of TB-500, the difference between TB-500 and BPC-157, and the legal and 503A questions — answered and cited.

Twenty-five questions about TB-500 — definition, mechanism, safety, the BPC-157 comparison, and access — each answered directly and cited where it makes a quantitative claim.

## Definition and identity

Short, direct answers to the most common TB-500 questions. Where a claim is quantitative, it cites a study in the references.

## What is TB-500?

TB-500 is the synthetic Ac-LKKTETQ heptapeptide carrying the actin-binding motif (residues 17–23) of the endogenous repair protein thymosin beta-4 [12]. Most published efficacy data are on the full-length protein, not the fragment, so the two are kept distinct throughout this binder [6].

## What does TB-500 stand for and what does TB stand for in TB-500?

TB references Thymosin Beta-4, the parent protein. TB-500 is a research and veterinary designation for its synthetic Ac-LKKTETQ actin-binding fragment — residues 17–23 of the 43-residue protein [12]. The "500" is a product/research designation, not a chemical descriptor.

## What is TB-500 used for in research?

In animal and in-vitro models, thymosin beta-4 (and its actin-binding region) is studied for cell migration, wound re-epithelialization, angiogenesis, anti-inflammatory and anti-fibrotic effects, and cardiac and neural repair [5]. These are research contexts for the protein and its motif, not demonstrated human uses for the fragment [6].

## Is TB-500 a steroid?

No. TB-500 is a synthetic N-acetylated heptapeptide (Ac-LKKTETQ) corresponding to the actin-binding region of thymosin beta-4 — a peptide fragment, not a steroid hormone [12]. It has no steroid ring system and works through actin binding, not through steroid-receptor signaling [1].

## How does TB-500 work?

Its LKKTETQ motif is the actin-binding core of thymosin beta-4, which sequesters monomeric (G-) actin 1:1 to regulate cytoskeletal dynamics, cell migration, angiogenesis, and anti-inflammatory and anti-fibrotic signaling [1][5]. Whether the isolated 7-mer reproduces this at research doses is not established in humans [6].

## TB-500 and BPC-157 in the Research Literature

TB-500 and BPC-157 are studied together so often that the comparison deserves its own divider. They are chemically unrelated research peptides, both studied for tissue repair, and both are unapproved. The questions below cover the difference and how the recent literature treats the pair.

## What is the difference between TB-500 and BPC-157?

They are chemically unrelated research peptides studied for tissue repair; TB-500 is the Ac-LKKTETQ actin-binding fragment of thymosin beta-4, while BPC-157 is a separate pentadecapeptide [12]. A 2026 Sports Medicine review lists both among unapproved peptides with animal-model promise but scarce human safety data and limited regulatory oversight [13].

## Safety questions

The side-effect and safety questions, answered from what the published record actually shows — including where it shows nothing.

## What are the side effects of TB-500?

No controlled human safety data exist for the fragment [6]. The closest human safety signal is the intravenous full-length thymosin beta-4 Phase 1 study, well tolerated to 1260 mg with only infrequent mild-to-moderate events [6]. The standing concerns are the tumor and angiogenesis signal and the purity problems of unregulated product [5][6].

## Does TB-500 cause cancer or promote tumor growth?

Thymosin beta-4 is overexpressed in several cancers and implicated in metastasis and tumor angiogenesis; the same pro-migratory, pro-angiogenic properties that aid repair are a theoretical oncologic safety concern [5]. No human safety conclusion for the TB-500 fragment exists, so a causal claim cannot be made in either direction [6].

## Is TB-500 safe for long-term use?

Long-term safety of the TB-500 fragment in humans is unknown — there are no controlled human trials of it [6]. The tumor and angiogenesis signal and the absence of regulatory oversight make long-term-use safety claims unsupported [5][6]. This site makes no use recommendation.

## Evidence and timeline questions

What is and is not established about TB-500's effects, and how the human and animal records line up.

## Are there any human clinical trials on TB-500?

There are no completed controlled trials of the TB-500 heptapeptide itself [6]. Human data exist only for full-length thymosin beta-4: a randomized placebo-controlled Phase 1 IV safety/PK study and topical ophthalmic (RGN-259) dry-eye RCTs; an injectable acute-MI trial completed, and an early injectable stroke trial was withdrawn [6][7][10][11].

## What is the latest research on TB-500 / thymosin beta-4?

Recent (2021–2026) thymosin beta-4 work spans engineered local-delivery cardiac scaffolds [16], cutaneous-flap survival via Wnt/β-catenin signaling [14], and a 2026 Sports Medicine review concluding that unapproved repair peptides show animal-model promise but scarce human safety data [13].

## Does TB-500 work for muscle tears and recovery from exercise?

In muscle injury, thymosin beta-4 acts as a myoblast chemoattractant in animals, but the controlled mdx-mouse study found more regenerating fibers without strength gains [5]. Human recovery efficacy of the fragment is unproven [6].

## How long does it take for TB-500 to work for injury healing?

No validated human timeline exists [6]. In a rat wound model, topical or intraperitoneal thymosin beta-4 raised re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline — an animal result, not a human dosing schedule [3].

## Can TB-500 help with tendon injuries and ligament repair?

Direct connective-tissue evidence is limited; the consolidated mechanism (migration, remodeling, fewer myofibroblasts) is the basis of interest [5]. Human tendon or ligament efficacy of TB-500 is unproven, and no completed controlled trial of the fragment exists [6].

## Does TB-500 affect the heart?

In mice, thymosin beta-4 activated PINCH–ILK–Akt survival signaling and improved cardiac function after coronary ligation, and a human acute-MI trial of thymosin beta-4 completed [2][10]. However, systemic thymosin beta-4 failed to reduce ischemia-reperfusion injury in a porcine study, so the cardiac record is not uniform [5].

## Does TB-500 promote angiogenesis and is that a safety concern?

Thymosin beta-4 drives endothelial migration and pro-angiogenic signaling [5]. Pro-angiogenesis aids repair but is also the basis of the tumor-angiogenesis safety concern, which is why this binder treats angiogenesis as both a mechanism and a caveat [5].

## Does TB-500 have neuroprotective effects on the brain?

In a rat embolic-stroke dose-response study, intraperitoneal thymosin beta-4 improved neurological function at 2 and 12 mg/kg but not at 18 mg/kg (non-monotonic; modeled optimum near 3.75 mg/kg) [4]. These are animal findings on the full-length protein [6].

## Does TB-500 increase hair growth?

Nanomolar thymosin beta-4 stimulated hair growth in rats and mice by activating hair-follicle bulge stem cells and increasing MMP-2 [5]. This is rodent data, not human evidence for TB-500 [6].

## Does TB-500 reduce inflammation?

Thymosin beta-4 suppressed TNF-α–induced NF-κB activation and IL-8 in vitro and showed anti-fibrotic effects across liver, renal and pulmonary animal models [5]. Human anti-inflammatory efficacy of the fragment is not established [6].

## Does TB-500 help wound healing?

In animal models the full-length protein accelerates dermal and corneal re-epithelialization, raises collagen deposition and angiogenesis, and reduces scarring; topical thymosin beta-4 (RGN-259) improved dry-eye signs in human RCTs [3][7]. Fragment-specific human wound efficacy is unproven [6].

## Access and regulatory questions

The legal and compounding questions, answered from the FDA-citable record. The full detail sits behind the [FDA 503A status of TB-500](/legal-status) divider.

## Is TB-500 FDA approved?

No. TB-500 has no approved therapeutic indication and is not an FDA-approved drug [18]. The FDA placed the entry it lists as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 (bulk substances that may present significant safety risks), effective with the September 29, 2023 nominated-substances update [18].

## Is TB-500 banned by WADA and in competitive sports?

Yes. TB-500 (and thymosin beta-4) fall under WADA's prohibited peptide, growth-factor and tissue-repair categories, banned in and out of competition; LC-MS assays detect it in equine and human matrices [6][17]. The fragment's chemical identity was published as a doping-control reference [17].

## Is TB-500 legal?

Legality depends on context, not a single yes or no. TB-500 is not an FDA-approved drug and was placed in 503A Category 2 for compounding, meaning it is not within the FDA's enforcement-discretion policy for 503A compounding while that status stands [18][19]. It is also prohibited in sport by WADA [6]. The compounding-access framework is detailed on the [TB-500 legal status](/legal-status) page; this is general information, not legal advice.

## Can you get TB-500 from a compounding pharmacy?

Under the current framework, no — not through routine 503A compounding. A compounder may use a bulk active ingredient only if it is eligible under the 503A/503B rules, and a Category 2 substance such as TB-500 is not eligible for routine 503A compounding while that status stands [19]. Legally compounded access in general requires a licensed-prescriber evaluation and a valid patient-specific prescription, with the ingredient-eligibility caveat applying [19]. This site names no pharmacy or provider and offers no way to obtain any substance.

## What is the FDA 503A status of TB-500?

The FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 (bulk substances that may present significant safety risks), effective with the September 29, 2023 update, citing concerns including potential immunogenicity for certain routes and a lack of important safety information [18]. "TB-500 (free base)" and "TB-500 acetate" appear on the published agenda of the July 23–24, 2026 PCAC meeting as substances being considered for the 503A bulks list — a scheduled discussion, not a decision or a change in status [20].

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A tabbed research binder on TB-500 and thymosin beta-4 — each evidence class filed behind its own divider and cited to source, the fragment kept apart from its parent protein, with no clinic behind the binder and nothing here dispensed or prescribed.