What Is TB-500 Frag? Dosage, Half-Life & How to Track It

What TB-500 Frag actually is (and why the name is misleading)

TB-500 Frag is marketed as a fragment of TB-500 (thymosin beta-4) — implying a smaller piece of the same healing molecule at a lower price. What is actually being sold under that name, in nearly every case, is Ac-SDKP (N-acetyl-Ser-Asp-Lys-Pro), also known by the generic name goralatide. It is a real, well-characterized natural peptide — but it is the fragment cleaved from the N-terminal end of thymosin beta-4, structurally and functionally unrelated to the actin-binding domain that gives full-length TB-500 its cell-migration effect.

That distinction matters because the two compounds do different jobs. TB-500 mobilizes repair cells throughout the body by binding G-actin. Ac-SDKP does not touch actin at all — its best-documented roles are keeping hematopoietic stem cells in a quiescent, non-dividing state, and acting as an antifibrotic signal that limits excess collagen deposition in the heart, kidney, and lung. Buying “TB-500 Frag” expecting TB-500’s wound-healing effect at a discount is buying the wrong peptide for that goal.

Ac-SDKP has one more genuinely notable property: it is the natural substrate of ACE (angiotensin-converting enzyme), the same enzyme ACE-inhibitor blood pressure drugs block. That is not a coincidence — part of why ACE inhibitors show antifibrotic benefits in the heart and kidney is thought to run through the resulting 5–10× rise in circulating Ac-SDKP levels, since ACE is what normally destroys it. This gives Ac-SDKP an unusually strong mechanistic backing for a research peptide, even though it was never developed as a self-administered injectable.

Typical dosing & reconstitution

Because Ac-SDKP is sold through the same research-peptide channels as BPC-157 and TB-500, it typically ships the same way: lyophilized powder reconstituted with bacteriostatic water. Community-reported protocols describe 100–300 mcg subcutaneously once daily, but this is worth being direct about — there is no clinical precedent for that route or schedule. Published Ac-SDKP research is dominated by continuous IV infusion in animal and small human cardioprotection studies, not a daily subcutaneous bolus.

At 1.0 mg/mL, a 200 mcg dose is 20 units on a standard U-100 insulin syringe. The reconstitution math is identical to any other lyophilized peptide — what is genuinely uncertain is whether the once-daily schedule reflects the compound’s actual pharmacology, given its 5-minute plasma half-life.

Half-life & what it means for frequency

Ac-SDKP clears from plasma extremely fast — roughly 5 minutes — because ACE degrades it almost as quickly as it appears, the same relationship that makes it accumulate when ACE is pharmacologically blocked. A once-daily subcutaneous injection produces a brief spike, not a sustained elevation, which is a mismatch with how the compound’s best-documented effects were actually studied — using continuous exposure, not a single daily peak.

This is the honest caveat that gets lost in “TB-500 Frag” marketing: a 5-minute half-life dosed once a day means blood levels are only meaningfully elevated for a small fraction of each 24-hour period. Whether that intermittent exposure produces any of the antifibrotic or stem-cell effects seen in continuous-infusion research is genuinely unknown.

What to track & common side effects

There is no established human side-effect profile for self-administered Ac-SDKP at research-peptide doses — the compound’s human data comes from IV infusion studies in specific clinical contexts, not from daily subcutaneous self-dosing. Reported issues in the research-peptide community mirror any small injectable peptide: injection-site irritation and occasional lightheadedness.

Given how thin the dosing evidence is, the useful thing to track is the plain record: dose, timing, and site, logged consistently enough that if anything changes — good or bad — you have an actual timeline to look at rather than a memory of “a few weeks ago.”

Frequently asked questions