Thymosin beta-4 fragment (Ac-LKKTETQ)
Usually the acetylated 7-amino-acid active fragment (residues 17–23) of thymosin beta-4. Some products sold as TB-500 contain the full 43-amino-acid protein instead.
Category 2 is FDA’s list of bulk substances that may present significant safety risks in compounding. The 503A bulks list adds substances that pharmacies may compound with. Advisory committee votes are advice; FDA makes the final decision. Sport status follows the WADA Prohibited List in force since January 1, 2026; athletes should confirm with their anti-doping organization. Checked October 5, 2026.
Loading: 2–2.5 mg twice weekly for 4–6 weeks.
Maintenance: 2–2.5 mg once weekly or every 2 weeks.
Load 5 weeks, maintain 6, then 6 off, shown over 26 weeks
The ways TB-500 is most often run, each tagged with where it comes from.
The usual pattern: about 4–5 mg a week to start, then roughly half. Untested in any human study.
A lighter schedule some guides use to hold gains after the loading phase.
How it’s taken in the premixed 1:1 blend. See BPC-157 + TB-500.
| Period | Dose | Draw at 5 mg/mL |
|---|---|---|
| Weeks 1–5 (2× per week) | 2.5 mg | 50 units (0.50 mL) |
| Weeks 6–11 (1× per week) | 2 mg | 40 units (0.40 mL) |
Units assume a 5 mg vial mixed with 1 mL. Use the calculator for other vial sizes.
Under the skin anywhere. Guides agree it acts body-wide, so it needn’t go near the injury. Rotate belly, outer thigh and upper arm.
No published guidance, and the guides checked don’t address it. Take it when you remember unless the next dose is close, then keep the usual days; don’t double up.
Some users report tiredness or headache during loading that fades after the first week or two.
CommunityGuides describe less pain and stiffness and better movement. Anecdotal only.
CommunityGuides say older or chronic injuries need the full 8–12 weeks. No human study of TB-500 has measured any benefit.
CommunityTiredness or lethargy in weeks 1–2 (community)
Common during loading. Usually passes on its own.
Headache (community)
Usually mild and early. Stop if it’s severe or doesn’t settle.
Injection-site redness, swelling or tenderness (community)
Mild. Rotate sites across belly, thigh and upper arm.
Nausea (community, rare)
Usually mild and around the time of injection.
Unknown safety of the fragment
Never tested in people. Full-length thymosin beta-4 was well tolerated in phase 1 IV trials, but that is a different molecule.
Hives, face or throat swelling, trouble breathing, chest pain or fainting; spreading redness, heat, pus or fever at a site; or any new lump, given the theoretical tumor concern.
No published human studies of TB-500 turned up in our October 2026 review. The evidence note at the top of this page sums up what is known.
| Vial | Water | Common dose | Draw | Strength | Action |
|---|---|---|---|---|---|
| 5 mg | 1 mL | 2.5 mg | 50 units (0.50 mL) | 5 mg/mL | |
| 10 mg | 2 mL | 2.5 mg | 50 units (0.50 mL) | 5 mg/mL |
Syringe units for common doses at different water volumes. Select a cell to open it in the calculator.
| Dose | Water added | ||
|---|---|---|---|
| 1 mL | 2 mL | 3 mL | |
| 2 mg | |||
| 2.5 mg | |||
| 5 mg | |||
U-100 insulin syringe: 100 units is 1 mL. Draws over 100 units show in mL. Faded values are under 2 units, which is hard to measure. Check that your vial holds the larger volumes.
Usually the acetylated 7-amino-acid active fragment (residues 17–23) of thymosin beta-4. Some products sold as TB-500 contain the full 43-amino-acid protein instead.
Not approved as a drug in the US or EU. Nomination withdrawn, so no longer in FDA Category 2 (April 2026). On July 23, 2026 FDA’s advisory committee voted 8 to 6, 1 abstaining, to recommend adding it to the 503A bulks list; FDA staff had advised against.
From community reports, not established: Loading: 2–2.5 mg twice weekly for 4–6 weeks. Maintenance: 2–2.5 mg once weekly or every 2 weeks. These are the amounts sources reference, not recommendations.
There’s no single right amount, because the water only sets the strength. With 1 mL of bacteriostatic water in a 5 mg vial, the strength is 5 mg/mL, so 2.5 mg is 50 units on a U-100 insulin syringe. More water makes small doses easier to measure. The dose chart above shows other volumes.
Before mixing: Freezer (about −20 °C) for long-term storage. After mixing: Fridge (2–8 °C); use within about 4 weeks. This is common practice; no product label covers it.
Yes. Named under S2.3 growth factors (“thymosin-beta-4 and its derivatives, e.g. TB-500”), banned at all times.
No published human studies turned up in our October 2026 review. The evidence note at the top of this page sums up what is known.
Doses tagged Community come from public dosing guides and user reports, checked against at least two of them. Those sites aren’t named here because many of them sell peptides or earn commissions on them.