What it is
Thymosin beta-4 (Tβ4) is a small protein, 43 amino acids long, found naturally in almost all human cells. It binds actin, the protein that builds a cell's internal scaffolding, and is involved in cell movement and wound repair.
TB-500 is the name the research-chemical market uses for a much shorter, synthetic piece of that protein: a 7 amino acid fragment covering the actin-binding region, listed by the US FDA as thymosin beta-4, fragment. This distinction matters. Most of the published research that gets cited to support TB-500, including the wound-healing and cardiac work, was done with the full 43 amino acid protein, produced under names like RGN-137, RGN-259 and RGN-352 by the company RegeneRx, not with the short fragment sold in research-peptide vials. Very little published work has tested the short fragment on its own.
How it works
The full-length protein binds monomeric actin and is thought to promote cell migration, reduce inflammation and support blood vessel growth, effects studied in skin wounds, corneal injury and heart tissue after a heart attack. The short fragment is built around the region of the protein believed to be responsible for the actin-binding activity, on the theory that this piece carries the useful part of the effect. Whether the isolated 7 amino acid fragment behaves the same way the intact 43 amino acid protein does in tissue has not been demonstrated in the published literature we could find.
What the research found
Full-length thymosin beta-4. This is where almost all of the substantive data sits.
- In mice, recombinant human thymosin beta-4 improved cardiac function after induced heart attacks, and a related 2025 study extended this to a small group of human patients with acute ST-elevation myocardial infarction after reperfusion, alongside the mouse work.
- As an eye drop (RGN-259), the full protein has gone through Phase 3 trials for neurotrophic keratitis and has been studied for dry eye disease, with the company reporting it as generally well tolerated across more than a thousand treated patients.
- Earlier small trials and reviews describe use of the full protein in chronic wounds such as pressure ulcers, venous ulcers and epidermolysis bullosa.
The short TB-500 fragment. Published data on the specific 7 amino acid fragment sold as TB-500, on its own, is thin. The clearest example is a 2026 rat study that gave BPC-157, TB-500 and the combination to rats with surgically cut Achilles tendons and compared healing on biomechanical and tissue measures. That is a rodent study, and it stands out mainly because so little else has tested the short fragment specifically rather than the full protein.
Side effects reported in studies
The full-length protein's human trials, run for eye and wound indications, are reported as generally well tolerated, with injection or application site reactions as the main issue noted in company and review summaries. That safety record does not automatically transfer to the short fragment given by subcutaneous injection, which has not gone through the same testing. The US FDA's nomination documents for both the fragment and BPC-157 raised the same generic concern: injectable compounded peptides can carry a risk of immunogenicity from aggregation or manufacturing impurities, and the agency said it lacked the data to know whether harm would result.
TB-500 vs full-length thymosin beta-4
| TB-500 (research market) | Full-length thymosin beta-4 | |
|---|---|---|
| Length | 7 amino acids | 43 amino acids |
| Route in trials | Not clinically trialled as this fragment | Eye drops, injection, topical gel |
| Human data | None found specific to the fragment | Phase 3 eye trials; small cardiac and wound studies |
| WADA status | Covered under thymosin beta-4 prohibition | Prohibited at all times |
Status in the Philippines
No TB-500 or thymosin beta-4 product is registered with FDA Philippines as a medicine, and it is not a controlled substance under RA 9165. It is sold locally by research-peptide suppliers, usually alongside BPC-157. Athletes should note that thymosin beta-4 is on the WADA Prohibited List regardless of which version is used. In the US, the short fragment was nominated in 2023 to FDA's list of bulk substances that may present significant safety risks for compounding and that nomination was withdrawn in April 2026, which is a procedural change, not an approval.
Local stock TB-500 10mg at Primara Labs, delivered in Metro Manila and nationwide. Research use only.
Storage
Keep the lyophilised powder refrigerated and away from light. Once reconstituted with bacteriostatic water, store at 2 to 8°C. During a brownout, move vials to a cooler with ice packs rather than leaving them in a fridge that is warming up. The TB-500 calculator and the reconstitution calculator handle the arithmetic. See the beginner guide for handling basics.
