TB-500
/T · B five hundred/aka Thymosin beta-4 fragment, Ac-LKKTETQ, Tβ4 17–23
A synthetic copy of the actin-binding region of thymosin beta-4, a protein that helps cells move into injured tissue in lab and animal studies.
TB-500: educational research discussion. Not medical advice. Not a protocol for you.Details
- Reported range
- 2–2.5 mg (loading)
- Frequency
- 2× weekly, then less often
- Cycle length
- 4–6 week loading block, then taper
- Half-life
- Unknown in humans
- Route
- SC (sometimes IM)
Reported figures describe what is published or discussed. None of them is a dose for you.
Mechanism
What it is proposed to do
Thymosin beta-4 (Tβ4) is a 43-amino-acid protein that binds G-actin, the building block of the cell's internal scaffolding, and is abundant in platelets and white blood cells. In cell and animal studies the full protein promotes cell migration, new blood vessel growth and wound closure, and dampens inflammation. Residues 17–23 (LKKTETQ) form the actin-binding site linked to cell migration. TB-500, in the analytical literature, is that stretch with an acetyl cap. Whether the isolated fragment reproduces the full protein's effects in people has not been tested.
- 01
TB-500
Acetylated LKKTETQ, residues 17–23 of Tβ4
established - 02
Actin-binding motif
Where full-length Tβ4 binds G-actin; the fragment alone is less studied
proposed - 03
Cell migration · angiogenesis
Shown for full-length Tβ4 in cell and animal models
proposed - 04
Faster repair in animals
Skin, eye and heart injury models, mostly with the full protein
proposed
Half-life. No human pharmacokinetic data for the fragment. Twice-weekly schedules are community convention, not derived from a measured half-life.
Dosing & cycles
What is reported, and where it comes from
Numbers below are labeled FDA label, clinical trial range or commonly reported range. They describe the published and discussed landscape. They are not instructions and not a protocol for you.
Dosing studio
Every figure is labeled by where it comes from.
Scale view: Commonly reported loading range
Probe at 2.25 mg: inside the reported band (2–2.5 mg). Drag it to read the scale. It does not pick a number for you.
Typical cycle, as a calendar
Loading block, then taper
4–6 weeks loading, then lower dosing
The most repeated community shape: twice weekly during a loading block, then smaller or less frequent doses, then off. Taper and break lengths are convention, not data.
Cycle patterns
Loading block, then taper
The most repeated community shape: twice weekly during a loading block, then smaller or less frequent doses, then off. Taper and break lengths are convention, not data.
Single short block
Some discussions describe one loading-style block with no maintenance phase. No human data compare this with longer use.
Stacks
What it gets combined with
Why people pair things, and what nobody has tested.
Wolverine stack
2 compounds- Why people combine these
- Pairs TB-500's proposed cell-migration effects with BPC-157's proposed angiogenic and fibroblast effects. Different mechanisms, same target tissue.
- Caution
- No human study has tested the pair. Both have proposed pro-angiogenic activity, so the theoretical cancer concern applies twice.
- What is unknown
- No published human data on this combination: dosing, interactions and long-term effects are all unstudied.
Pre-mixed repair blends
3 compounds- Why people combine these
- Research-market blends put TB-500, BPC-157 and GHK-Cu in one vial, pitched at skin and soft-tissue repair.
- Caution
- Fixed ratios nobody tested, three unverified ingredients, and no way to tell which one caused a reaction.
- What is unknown
- No published human data on this combination: dosing, interactions and long-term effects are all unstudied.
Also sold in pre-mixed blends
What a blend changesIn a blend, TB-500 cannot be adjusted on its own, and the mixture has no human data of its own. Typical vial formats shown; labels vary.
Evidence
How much of this is known
Evidence grade
C
Thin human data
Human data thin (pilots, uncontrolled, or none completed). Strong animal data and a lot of anecdote.
How we gradeGrade C mostly on borrowed evidence. Full-length thymosin beta-4 has small human trials with mixed results. The fragment sold as TB-500 has essentially none.
Human trial status
We found no published human trials of the TB-500 fragment. Full-length thymosin beta-4 was tested by RegeneRx and partners: RGN-259 eye drops in dry eye and neurotrophic keratopathy (Phase 2 and 3; the 18-patient SEER-1 trial was closed early, and its primary endpoint was significant by one statistical test and not by another), RGN-137 skin gel in venous leg ulcers (Phase 2), and IV safety studies in healthy volunteers. None led to approval.
Limitations
- The fragment and the full protein are different molecules. Evidence for one does not transfer automatically to the other.
- Human trials of the full protein used eye drops, skin gel or IV infusion, not the SC injections discussed online.
- Most mechanistic and animal work used full-length thymosin beta-4.
- FDA staff recommended against adding it to the 503A bulks list in 2026, citing characterization and safety questions.
Sources to read
- Esposito S et al. Synthesis and characterization of the N-terminal acetylated 17–23 fragment of thymosin beta 4 identified in TB-500 (Drug Test Anal 2012)
- Sosne G, Dunn SP, Kim C. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial (Cornea 2015)
- 0.1% RGN-259 (thymosin β4) ophthalmic solution in neurotrophic keratopathy: randomized, placebo-controlled, double-masked phase III trial (SEER-1)
- Guarnera G, DeRosa A, Camerini R. The effect of thymosin treatment of venous ulcers (Ann N Y Acad Sci 2010)
- Ruff D et al. Randomized, placebo-controlled, single and multiple dose study of intravenous thymosin β4 in healthy volunteers (Ann N Y Acad Sci 2010)
- FDA Pharmacy Compounding Advisory Committee, July 23–24, 2026
Links open PubMed, DailyMed, FDA or trial-registry searches. We do not cite what we have not described accurately.
Safety
Side effects, cautions, status
Commonly reported effects
- Injection-site redness or irritation.
- Anecdotal fatigue or headache.
- Product identity is a real problem: a vial labeled TB-500 may contain the fragment, the full 43-amino-acid protein, or something else.
- Theoretical concern: Tβ4 promotes cell migration and blood vessel growth, and high Tβ4 expression has been associated with tumor spread in some laboratory and tissue studies. No human data address whether dosing it changes cancer risk.
Who should be extra cautious
- Active or past cancer. Pro-migration and pro-angiogenic biology is a theoretical concern with no human data to settle it.
- Pregnancy or breastfeeding. No data at all.
- Tested athletes. Prohibited at all times (WADA S2.3). Anti-doping labs have published methods to detect it.
- Gray-market product. The label may not say whether the vial holds the fragment or the full protein. Purity and endotoxin also vary.
Legal & regulatory status
Not approved as a drug anywhere. Full-length thymosin beta-4 reached clinical trials but was never approved. In April 2026 FDA removed the thymosin beta-4 fragment from its Category 2 compounding-risk list. In July 2026 an FDA advisory committee recommended it for the 503A bulks list. Until FDA finishes rulemaking, that is a recommendation, not permission to compound.
2026 compounding context. July 23–24, 2026: FDA's Pharmacy Compounding Advisory Committee recommended the thymosin beta-4 fragment (TB-500) for the 503A bulks list, against the advice of FDA staff, who raised characterization and safety concerns. Legal compounding requires a final FDA rule.
WADA. Prohibited at all times. Thymosin-β4 and its derivatives, e.g. TB-500, are named under S2.3 (growth factors and growth factor modulators).
Storage & handling, high level
Sold as lyophilized powder. Reconstituted peptides are generally kept refrigerated, away from light, and degrade over weeks. Knowing which molecule is in the vial matters more than any storage detail.
Reconstitution and injection technique are clinical skills. The reconstitution calculator does arithmetic only.
FAQ
Questions people ask about TB-500
Is TB-500 the same as thymosin beta-4?
Were there human trials?
Is TB-500 legal to compound now?
Why is it banned in sport if nobody knows whether it works in people?
Does it heal injuries faster?
The monthly Evidence Brief
Keep up with the evidence
One email a month: new trials, grade changes and FDA or WADA updates across the whole atlas, TB-500 included. You get the free guide right away.
Free guide · PDF
10 Peptide Claims, Fact-Checked
13 pages · sent to your inbox right away
Email only. Unsubscribe from any email in one click. We do not sell or rent your address. Nothing we send is medical advice. Privacy