TB-500: evidence, safety and FDA status

TB-500 appears in recovery offers alongside BPC-157. The first question is which molecule a seller means: the seven-amino-acid fragment or full thymosin beta-4. FDA’s 2026 assessment concerns the defined fragment ^[1]. Newer clinical reports must be read for product identity, co-treatments and study design, rather than folded into a blanket claim that every use is proven or that no human report exists.

TB-500 is a seven-amino-acid piece of thymosin beta-4

TB-500 is the lab-made fragment Ac-LKKTETQ, while the natural protein thymosin beta-4 is 43 amino acids long ^[1]. The fragment copies amino acids 17 to 23 of the protein and adds an acetyl group to the first one. FDA's 2026 briefing calls it a synthetic N-acetylated heptapeptide, which is chemistry for a capped seven-unit chain.

Why that stretch? Researchers studying the full protein linked the LKKTET segment to binding actin, a structural protein cells use to move and close wounds ^[1]. TB-500 was built on the idea that the short piece might carry the protein's repair effects on its own. Clinical benefit of the verified fragment remains unestablished.

You will see it labeled TB-500, TB-500 acetate, TB-500 free base or "thymosin beta-4 fragment". Many sellers also call it plain "thymosin beta-4". FDA evaluated both the free base and the acetate salt, because it was unclear which one the original nominator meant ^[1].

Why "TB-500" and "thymosin beta-4" are not the same product

The two names are often used as if they were interchangeable, but FDA reviewed the fragment, and selected controlled human trials used the full protein. That gap matters more than anything else on this page. A result in one molecule does not carry over to the other without a study that shows it does.

FDA made the same point in its briefing. It noted that findings for the non-acetylated LKKTETQ sequence "cannot be directly extrapolated" to TB-500, the acetylated version sold today ^[1]. It also found a lab study in which TB-500 did not speed wound closure in fibroblast cultures ^[1].

Human evidence: distinguish the fragment, mixed treatments and full protein

The current registry search returned NCT07487363, but its own summary calls it a fictional example of a ClinicalTrials.gov-style record. A structured recruiting label is therefore not sufficient to present it as a verified active trial. It has no posted results. This anomalous entry does not establish human efficacy or authorization ^[9].

FDA’s assessment found no human pharmacokinetic or treatment studies for the defined TB-500 free base or acetate. Its FAERS search through March 26, 2025 retrieved no reports; a separate food/supplement complaint search found two blended-product cases without safety assessments ^[1]. These findings describe those searches. They do not prove no person has been exposed, or that later reports cannot appear.

The trial most often linked to TB-500 is a phase 2 study of thymosin beta-4 eye drops (0.1%, sold in trials as RGN-259) in 9 people with severe dry eye ^[5]. At day 56, eye discomfort was 35.1% lower than with the vehicle drops (P=0.0141), and corneal staining was 59.1% lower (P=0.0108) ^[5]. It is a real randomized trial. It is also the wrong molecule, the wrong route and a tiny group, so it tells you nothing direct about an injected seven-amino-acid fragment.

What TB-500 is claimed to do vs what has been tested

A 2026 Achilles-tendon experiment used 32 male rats in four groups of eight. It reported histological and biomechanical differences, including improved load to failure in the TB-500 group and no additional combination benefit. The abstract calls the material synthetic thymosin beta-4/TB-500 without establishing the seven-residue identity. Animal injury repair, product identity and human function are separate questions ^[8].

FDA’s assessment did not establish clinical effectiveness of the defined fragment for wound healing. It describes marketing claims for tissue repair, tendons, muscle, ligaments and bones, but found no applicable clinical treatment evidence ^[1]. A newer rat Achilles-tendon study does not fill the human-outcome gap ^[8].

So when people ask whether BPC-157 and TB-500 build muscle, or what the pair does, the honest answer is that nobody has measured it in people. The claims come from animal work, from the larger protein, or from marketing.

BPC-157 and TB-500 together: what's known

A three-case October 2026 report describes dental or surgical nerve injuries treated with a mixture naming TB-500, BPC-157 and ARA-290, alongside dexamethasone and local anesthetics. Reported subjective improvement cannot identify which component helped, exclude spontaneous recovery, or establish a safe treatment protocol ^[7]. The article does not report sequence or analytical identity verification for the substance called TB-500. It therefore does not establish efficacy of FDA’s specific Ac-LKKTETQ fragment.

FDA’s food/supplement complaint search covered January 2004 through March 10, 2025 and found two cases naming blended TB-500 and BPC-157, without safety assessments. Those reports do not independently verify product contents or causation ^[1]. A separate knee report used BPC-157 with full thymosin beta-4; that must not be relabeled a verified TB-500-fragment trial. For the distinctions, compare BPC-157 and TB-500 and BPC-157’s human evidence.

Safety: what FDA says it can't rule out

FDA identifies important safety gaps, including immune reactions, aggregation and peptide-related impurities ^[3]. The newer three-case report observed no adverse effects, but that small, uncontrolled series cannot exclude uncommon, delayed or treatment-specific harm ^[7]. Unknown risk must not be translated into either established safety or a known event rate.

FDA is particularly concerned about the absence of human data on drug products containing these substances administered via any ROA.^[1]

• Immune reactions. As an injected peptide, TB-500 may provoke an immune response, a risk FDA says can be amplified by aggregation (peptide chains clumping together) and by impurities left from manufacturing ^[1].
• Unknown quality. FDA found no physical and chemical characterization data adequate to judge the substance, and no carcinogenicity studies ^[1].
• No reports is not the same as safe. FDA's adverse-event search found nothing, and FDA itself warns that its reporting system is voluntary and incomplete, especially for compounded products ^[1].

FDA status and current pharmacy requirements

FDA’s briefing proposes against adding TB-500 free base or acetate to the 503A bulks list. That is an agency assessment, not an approval or a final listing rule ^[1]. The current 503A regulation does not list TB-500, while FDA’s interim nomination document places the withdrawn nomination among substances previously in Category 2. Withdrawal does not itself establish ordinary retail eligibility ^{[11] [4]}.

A compounding advisory vote is advice to FDA. This page does not use a secondary report of a vote as proof of a changed legal status. An OIRA entry for a pending peptide-compounding access policy is also not issued guidance or a final rule ^[10]. Authorized clinical investigation under the IND framework has its own requirements and must be distinguished from a clinic selling a compounded prescription ^[12].

Can you get TB-500 through a pharmacy? Not right now

No FDA-approved TB-500 product is established by the reviewed sources. For ordinary 503A bulk compounding, an applicable USP/NF monograph, approved-drug-component route or final bulk listing must be evaluated; current records do not establish one for this fragment ^{[1] [11]}. A research-use label does not make a product approved for treatment. Authorized investigation is a separate regulated pathway ^[12].

A clinic’s statement that a licensed pharmacy supplies a product does not itself establish eligibility of that ingredient or a particular prescription. Ask for the exact molecule, dispensing facility and legal basis. The related BPC-157 approval guide and legal-status guide explain why approval, nomination and authorized research are different questions.

TB-500 is banned in sport at all times

WADA’s 2026 Prohibited List names thymosin beta-4 and derivatives such as TB-500 under S2.3, prohibited at all times ^[6]. A prescription alone does not remove that restriction. Athletes need advice through their governing anti-doping organization about applicable rules and any exemption process.

How to read a TB-500 offer

Start with molecular identity. A product called thymosin beta-4 may refer to the full 43-amino-acid protein, while the FDA-assessed TB-500 fragment has seven. Ask about the named pharmacy, product testing and legal basis. An unanswered question leaves uncertainty; it does not prove the seller’s contents or manufacturing practices.

Next, compare the claims with the tables above. A page promising faster tendon healing from TB-500 is describing animal or lab work, not trials in people. For how this site rates providers and the checks behind each rating, see how we check. For the companion peptide's safety record, see Is BPC-157 safe?

Terms used on this page