TB-500

Repair & healing

Also known as Ac-LKKTETQ, thymosin beta-4 fragment 17-23

A seven-amino-acid fragment of thymosin beta-4. Not the same molecule as thymosin beta-4 itself.

Read this first

Two chemically different molecules are sold as 'TB-500': this 7-residue fragment and full-length 43-residue thymosin beta-4, which is roughly 5.6 times heavier. All published clinical data belongs to the full-length peptide. There is no way to tell which is in a vial without mass spectrometry.

How it works

Carries the actin-binding LKKTETQ motif from thymosin beta-4, which sequesters G-actin and regulates cell motility and cytoskeletal remodelling during tissue repair.

SubcutaneousIntramuscular

In the body

No plasma curve is shown for this compound.

Unknown. No pharmacokinetic study of this fragment exists in any species. The widely repeated claim of a multi-day half-life has no source and is contradicted by full-length thymosin beta-4, which clears from human plasma in 0.5 to 2 hours.

Doses

2 mg, 2.5 mgtwice weekly loading, then weeklyCommunity practice

Community loading protocol for 4 to 6 weeks, then maintenance. No clinical trial has ever used the subcutaneous route.

Vial sizes

2 mg5 mg10 mg

Commonly treated as good for 28 days refrigerated once reconstituted.

Side effects

No human safety data for this fragment exists.
Full-length thymosin beta-4 showed no dose-limiting toxicity across intravenous doses from 42 to 1260 mg.

Cautions

Known or suspected cancer. Thymosin beta-4 overexpression in melanoma produced a 2.3-fold increase in cell migration and a 4.4-fold increase in tumour vessel count, and it is overexpressed in colon, pancreatic, renal and lung tumours.
Prohibited in sport at all times. WADA names it explicitly under S2.3: 'Thymosin-β4 and its derivatives, e.g. TB-500'.

Status

Not approved. An FDA advisory committee voted 8 to 6 in favour of the 503A compounding list in July 2026; that vote is non-binding.

Sources

Reference information for personal record-keeping. Not medical advice, and not a recommendation to use any of these compounds.