TB-500

Also called TB-500 acetate, Ac-LKKTETQ, thymosin β4 fragment 17–23. Not the same as thymosin β4 (Tβ4)¹

TB-500 is a synthetic 7-amino-acid peptide, not thymosin β4. FDA says plainly that "thymosin beta-4 and TB-500 are not the same substance." TB-500 is a short, acetylated piece of thymosin β4 (Tβ4), and FDA found no study in which it was given to people.¹ The human trials often quoted for TB-500 used full-length Tβ4, and those efficacy trials mostly missed their main goals.^{15, 19, 20} In the one rat tendon study of TB-500, it did improve healing.⁵ Since October 28, 2026, HHS has said it won't act against licensed pharmacies that compound the acetate as an injection with a prescription. That is not FDA approval.^{6, 8}

Often paired with BPC-157. See BPC-157 vs TB-500

At a glance

Where to get it

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Molecular structure

A straight chain of 7 amino acids with an acetyl cap on the first one. The cap is what separates TB-500 from plain LKKTETQ.

The N-terminal acetyl group

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AcacetylLLeuKLysKLysTThrEGluTThrQGln

Sequence

Ac-LKKTETQ-OH

Position

Residues 17–23 of thymosin β4

Length

7 amino acids + acetyl

Formula

C38H68N10O14

Weight

889.01 g/mol

Acetate

C38H68N10O14 · CH3COOH, 949.1 g/mol

CAS

885340-08-9 (free base). None for the acetate

FDA UNII

QHK6Z47GTG (free base). None for the acetate

Drawn from the sequence FDA lists. Formula and weight are for the free base as given by FDA; the acetate figures are from FDA and HHS.^{1, 3}

What it is

FDA defines TB-500 as "a seven amino acid synthetic fragment of thymosin β4 and an acetyl group at the N-terminal amino acid." It appears to have first been made in 2003. "TB-500" is a common name, not an official drug name.¹ Research funded by WADA identified the active content of products sold as TB-500 as "the N-terminal acetylated 17-23 fragment of thymosin beta4 (Ac-LKKTETQ)."¹⁴

Three molecules that get mixed up

FDA notes that "several websites state that TB-500 is a synthetic version of thymosin beta-4 and often use the terms interchangeably." They are different substances.¹ FDA also found identity problems in what was submitted to it: the nomination listed a CAS number and formula that "matches neither TB-500 free base nor TB-500 acetate," and the papers reviewed don't clearly say which form they studied.^{1, 2}

How it works

No one knows how TB-500 itself acts in the body. The theory comes from its parent protein.

• Actin binding. Thymosin β4 holds single actin units and helps regulate cell shape and movement.^{1, 13} FDA describes a 6-amino-acid segment, LKKTET, as Tβ4's actin-binding region. TB-500 contains that segment.¹
• Cell migration and blood vessels. In rats, full-length Tβ4 sped wound closure and increased new blood vessel growth.²² In mice with a blocked heart artery, it improved heart-cell survival and heart function.²³ These are Tβ4 results, not TB-500 results.

Two FDA-reviewed findings cut against simple extrapolation. A 2024 lab study found the TB-500 free base "appeared to be devoid of wound-healing properties" in a cell scratch test. A 2003 mouse study that did show benefit used the non-acetylated fragment, which FDA says "cannot be directly extrapolated to the N-acetylated heptapeptide TB-500."¹

Evidence map

Each claimed use is graded for TB-500 itself. Trials of full-length thymosin β4 don't count toward these grades.

Scale: 5 FDA-approved, 4 strong human, 3 limited human, 2 animal or lab only, 1 anecdotal

Studies of TB-500 itself

FDA's summary: the nominator "did not submit, and FDA did not identify," published nonclinical in-vivo studies of TB-500's effects on wounds.²

The thymosin β4 trials (not TB-500)

Sellers often cite human trials as TB-500 evidence. Every one of them used full-length thymosin β4: RegeneRx's eye drops (RGN-259), skin gel (RGN-137) or IV form (RGN-352), or a Chinese recombinant Tβ4 (NL005).^{15, 16, 20, 21, 40, 41, 42} None tested TB-500, which is a different molecule given a different way; FDA found no study in which TB-500 was given to humans.¹

Taken together, safety in the Tβ4 trials looked clean, but every efficacy trial with a reported primary result missed it. Tβ4 has no regulatory approval for any use in the sources we reviewed. None of this transfers to TB-500.¹

By goal

Pick your goal to see what the evidence supports.

How it's used

TB-500 is sold as an injection. The HHS policy covers it only under the skin or into muscle; nasal, oral and topical TB-500 are outside it.^{3, 9}

No human study has tested any dose, and there is no human data on how the body absorbs or clears it by any route.^{1, 2} The 2026 rat study gave a daily injection into the belly for 4 weeks.⁵ Per-kilogram human doses seen online have no study behind them. We don't give a dose.

Side effects and who should avoid it

• No human safety data. FDA is "concerned about the lack of human data on drug products containing TB-500," and says the potential risks to people are unknown.²
• No toxicology. No acute, repeat-dose, genetic, reproductive or cancer studies were submitted or found.¹
• Immune reactions. FDA says injectable peptides "may pose a significant risk for immunogenicity, potentially amplified by aggregation." No such data were provided for TB-500.²
• Quality. The acetate certificate FDA reviewed capped total impurities at 2% but didn't identify them. The free-base certificate lacked assay, impurity, endotoxin and aggregate testing.¹
• Cancer. There is no evidence TB-500 causes cancer, and no study has tested whether it does. FDA's written review raised no cancer finding; its concern was the missing studies.¹ At the July 2026 advisory meeting, FDA and several panelists reportedly focused on a potential cancer signal.¹⁰ The worry rests on the parent protein: Tβ4 is often highly expressed in some cancers, and another Tβ4 fragment, Ac-SDKP, is raised in tumor tissue. Both findings are correlational and neither is about TB-500.^{24, 25} HHS called the safety concerns "inferential or mechanistic rather than observed," as reported by AJMC.⁹
• Reported side effects. FDA's adverse event database had no TB-500 reports through March 26, 2025; FDA says that "does not imply that the substance is safe." Its food complaint system had 2 cases of "blended TB-500 and BPC-157."^{1, 2} One of three FAERS reports on BPC-157 involved a BPC-157 + TB-500 "research purposes only" product.³⁶
• Athletes. Prohibited at all times under WADA S2.3. The HHS policy doesn't change that.⁴
• Pregnancy, breastfeeding, active cancer. No human data and no reproductive studies.¹ Ask a clinician.

Compared with

Sources: Biçer 2026,⁵ FDA briefings,^{1, 36} HHS Appendix B,³ WADA 2026 list.⁴ Full comparison: BPC-157 vs TB-500

Stacks

TB-500 is sold mostly in blends. Only one has been tested, in rats, and it added nothing. All blends fall outside the HHS policy.

Myths vs evidence

All options and prices

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Licensed compounding, with a prescription

As of May 2026, FDA found no pharmacies compounding TB-500.¹

Blends and research vials, outside the policy

Some storefronts sell TB-500 in Wolverine, GLOW or KLOW blends. The HHS policy covers single-ingredient products only, so we don't list them.^{3, 34} The policy also excludes research chemicals.⁷ In August 2026 FDA warned five peptide sellers that a "research use only" label doesn't excuse products clearly meant for people.³⁵

Legal status history

Newest first.

1. Current statusNov 1, 2026HHS says it won't take action against licensed 503A pharmacies, federal facilities and licensed physicians that compound single-ingredient TB-500 acetate, under the skin or into muscle, with a prescription. The policy is interim and open for comment, and state rules still apply. Not FDA-approved. Banned in sport.^{3, 7, 4}
2. Next · no dateA formal rule to add TB-500 to the 503A bulks list; none proposed yet. Comments on the HHS policy are due 2 weeks after Federal Register publication, about Nov 13, 2026 if it ran Oct 30 as scheduled (our calculation).^{6, 8}
3. Oct 28, 2026HHS enforcement discretion policy for TB-500 acetate and five other peptides. Docket HHS-OASH-2026-0496. Not FDA approval; HHS may revisit it if safety or quality signals arise.^{6, 8}
4. Oct 14, 2026The interim access policy is sent to the White House budget office for review.³⁹
5. Jul 23, 2026FDA's compounding advisory committee votes 8–6–1 to recommend adding both the free base and the acetate, for wound healing. FDA staff recommended against. The vote is advisory, and the count comes from law-firm reports.^{10, 11}
6. May 15, 2026FDA's review memo recommends not adding TB-500 to the bulks list, citing poor characterization, no history of compounding use, no evidence of effectiveness and no human safety data.¹
7. Apr 22, 2026Removed from Category 2 (announced Apr 15) with 11 other peptides after nominations were withdrawn. This did not move it to Category 1. A Federal Register notice of Apr 16 put TB-500 on the July meeting agenda.^{3, 38, 27}
8. Sep 29, 2023Placed in FDA's Category 2, substances that may pose significant safety risks in compounding.³
9. 2013US horse racing's medication consortium says TB-500 should be a Class A prohibited drug. WADA funds research to detect it.^{28, 14}

What the HHS policy covers

Sources: HHS Appendix B,³ BakerHostetler,⁷ FDA Law Blog,⁸ AJMC,⁹ Frier Levitt.³⁴

In sport

WADA's 2026 Prohibited List names "Thymosin-β4 and its derivatives e.g. TB-500" under S2.3, growth factors, prohibited at all times. That is a different class from BPC-157, which sits under S0.⁴ Sport Integrity Australia lists TB-500 as another name for thymosin β4, "banned in sport at all times."³⁰ WADA's 2027 list takes effect January 1, 2027. A summary of it lists no change to S2; we have not read the full list.³¹ In 2016, the Court of Arbitration for Sport banned 34 past and present Essendon AFL players for using thymosin β4.²⁹

FAQ

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References