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Recovery & healing

TB-500 / Thymosin Beta-4

A naturally occurring wound-response peptide released by platelets, used for muscle, tendon and neurological healing, often stacked with BPC-157.

Research chemical Recovery & healing

Reviewed 2026-09-12
Full name
Thymosin Beta-4 (full sequence) — products sold as 'TB-500' may contain either the full 43-amino-acid Tβ4 or just its Frag 17-23 fragment
Also known as
TB-500, TB4, Thymosin β4, Frag 17-23
Regulatory status
Research chemical for the self-administered market. The active molecule (Tβ4) has gone through legitimate pharmaceutical development under RegeneRx as RGN-259 (eye drops, completed Phase III), RGN-352 (systemic injection, completed Phase I) and RGN-137 (topical gel, Phase II) — but none of these are approved, marketed drugs.
Variant note
Sometimes sold as 'TB-500 Frag' or 'Thymosin Beta-4 Fragment' — a shorter fragment of the same parent protein, marketed as a cheaper alternative. It is not established as pharmacologically equivalent to full TB-500/Tβ4, and independent evidence for the fragment specifically is essentially absent; treat fragment products as a distinct, far less characterized compound rather than an interchangeable substitute.

Origin

Thymosin Beta-4 is a 43-amino-acid peptide present in nearly all human cells, especially platelets and white blood cells, released at wound sites as part of the natural clotting and repair cascade. 'TB-500' is a commercial name that's ambiguous: some vendors sell the full Tβ4 sequence, others sell only its Frag 17-23 region (LKKTETQ), the piece responsible for actin-binding and cell-migration effects. Check what a specific product actually contains before assuming.

Mechanism

Different regions of the Tβ4 sequence do different jobs: amino acids 1-4 are anti-inflammatory and anti-fibrotic; 1-15 is anti-apoptotic/cytoprotective; 17-23 drives actin binding, cell migration, angiogenesis and dermal wound healing (and triggers mast-cell degranulation); 40-43 supports cardiac cell migration after ischemic injury. TB4 binds free actin monomers (G-actin) rather than a conventional receptor, effectively expanding the pool of building blocks cells use to rebuild cytoskeletal structure during repair.

Research summary

Evidence

A 2015 meta-analysis found broad applicability across tissue regeneration, post-heart-attack cardiac repair, stroke and neurological recovery, kidney/liver repair, and bone/ligament/spinal cord injury in animal models. Human data is more substantial than for most research peptides: RGN-259 eye drops completed Phase III trials for dry eye and neurotrophic keratitis with statistically significant symptom improvement and no adverse events. RGN-352 systemic IV dosing was tested up to single doses of 1260 mg and repeated daily dosing for 14 days (cumulative ~18.9 g in one subject) with no dose-limiting toxicity, no cardiovascular/respiratory signal, and no cancers at 6-month follow-up; headache was the only adverse event, occurring equally in placebo. Pharmacokinetics show a short half-life (under 1-2 hours even at high doses) and dose-independent clearance, so TB4 doesn't meaningfully accumulate with daily dosing at the doses studied.

Evidence tier: Research chemical — see the methodology note for how this is assessed.

Citations

Reported benefits

  • Faster recovery from muscle strains and tears
  • Reduced muscle spasticity / tightness (notably reported by people with hypermobility disorders)
  • Support for tendon and ligament healing, often paired with BPC-157
  • Reported improvements in flexibility, which some users find beneficial and others find undesirable (increased joint laxity)

Dosing protocols reported in the literature & community

These are protocols reported by compounding pharmacies, published trials, or self-experimentation communities — not a prescription. Start low, especially for anything new.

Reported dosing protocols
RouteReported protocol
Subcutaneous injection — loading protocolA widely circulated protocol: 5 mg twice weekly (e.g. Monday/Thursday) for 5 weeks, then 5 mg once weekly for 2 more weeks (total ~35 mg over 7 weeks).
Subcutaneous injection — daily lower-dose protocolAlternative protocols use smaller daily doses: roughly 450-750 mcg per day for 20-30 days. Because Tβ4's half-life is short and it doesn't accumulate systemically, both large-infrequent and small-frequent dosing schemes appear in the literature with good animal results; there's no head-to-head human comparison.
Post-injury / acute dosingSome practitioners use a short course of higher daily dosing (e.g. ~1.5 mg/day for about a week) immediately after an acute injury or surgery, on the theory of mimicking the natural post-injury Tβ4 spike, then tapering to a lower maintenance dose.

Side effects

  • Injection site irritation
  • Possible mast-cell activation from the Frag 17-23 region — a concern for people with MCAS
  • Theoretical proliferative/metastasis-promoting risk, since Tβ4 overexpression is associated with several cancer types at the cellular level (no data yet on whether exogenous dosing carries this risk in humans) — TB4 is generally considered contraindicated for anyone with active or recent cancer

Safety notes

Safety: Human injection safety data (RGN-352 Phase I) is reassuring at doses far higher than self-experimenters typically use: no dose-limiting toxicity, no cancer signal at 6-month follow-up. But that was a short trial in healthy volunteers, not a long-term study, and the theoretical cancer-proliferation concern from cell-biology data means anyone with a personal or strong family history of cancer should weigh that risk carefully and ideally talk to a physician.
Community & reddit notes (anecdotal — not clinical evidence)

Frequently stacked with BPC-157: BPC for connective tissue and gut, TB4 for muscle, systemic inflammation and flexibility. People with Ehlers-Danlos/hypermobility spectrum disorders report mixed results on flexibility; most find reduced muscle spasticity helpful, a minority report an unwanted increase in joint hypermobility during use. Community also disputes what's actually being sold as 'TB-500': cheaper vials are more likely the smaller Frag 17-23 fragment rather than full Tβ4. That's not necessarily a scam (Frag 17-23 delivers more molecules per mg and covers the muscle/actin-binding effects), but buyers should know which one they're getting if they want Tβ4's broader immune and cardiac-repair activity too. Separately, some in the EDS/HSD community flag that TB-500's active sequence includes a region known to activate mast cells, and suggest starting low for anyone with Mast Cell Activation Syndrome (MCAS) or a history of mast-cell reactivity.

Used in stacks

Community combinations that include TB-500 / Thymosin Beta-4 — see each stack page for the combination-specific rationale and evidence.

Mixing compatibility

Pulled from a community-charted mixing-compatibility reference (anecdotal, clinic-use, and community-reported signals) — not a safety guarantee. Verify independently before combining anything.

Used together in wellness-clinic protocols

Reported as a combination to avoid