Research review · Sources checked October 15–31, 2026

Published February 14, 2026 · Updated October 31, 2026

TB-500: what the research shows

TB-500 is sold as a synthetic version of a short region of thymosin beta-4 (N-acetylated LKKTETQ). It is not an FDA-approved drug, and FDA reports no human exposure data for it.[1][2][3]

What TB-500 is

Doping-control laboratories identified the N-acetylated 17–23 fragment of human thymosin beta-4 (Ac-LKKTETQ) as the key ingredient in TB-500 products.[1] The LKKTETQ segment is the region of thymosin beta-4 associated with actin binding and cell migration; TB-500 was described as a veterinary preparation, and racing laboratories have developed assays to detect it in horses.[4]

Regulatory status

No FDA-approved drug product contains TB-500 or thymosin beta-4; a Drugs@FDA search returns no approved application.[2] FDA lists “Thymosin beta-4, fragment (LKKTETQ), also known as TB-500” among substances previously placed in category 2 of its compounding interim policies whose nominations were withdrawn. FDA states it “has not identified any human exposure data” for drug products containing the fragment and flags aggregation, impurities, and immunogenicity risk.[3]

Update, October 28, 2026: HHS made public a draft enforcement-discretion policy that lists TB-500 among six peptides (the others are BPC-157, epitalon, KPV, MOTS-c and semax). HHS says it does not intend to take enforcement action against state-licensed pharmacies, federal facilities or licensed physicians that compound these peptides under 10 conditions.[8] For TB-500, Appendix B names TB-500 acetate, for subcutaneous or intramuscular injection only.[8] The conditions include bulk powder from an FDA-registered facility with a certificate of analysis, one listed active ingredient per product, reporting of serious adverse events and a patient-specific prescription.[8] HHS calls the document a draft, open to comment on regulations.gov (Docket No. HHS-OASH-2026-0496) until 2 weeks after its October 30, 2026 Federal Register publication (November 13, 2026, per regulations.gov), and says it is not binding and may be revisited if a safety signal or quality problem arises.[8] This is not an FDA approval: compounded drugs are not reviewed by FDA for safety or effectiveness, and the policy records that FDA’s drug center recommended against listing TB-500.[8] For what it does and doesn’t change, see our FDA peptide policy explainer. This summary is not legal advice.

Full-length thymosin beta-4 is a different molecule

Human trials have studied the full 43-amino-acid thymosin beta-4, not TB-500. In a phase 1 study of 40 healthy volunteers, intravenous thymosin beta-4 at 42–1,260 mg daily for 14 days had infrequent, mild-to-moderate adverse events and no dose-limiting toxicity.[5] A phase 2 study of a topical thymosin beta-4 gel in 73 patients with venous ulcers found safety comparable to placebo and suggested a possible healing effect at one dose.[6] These results cannot be transferred to a 7-amino-acid fragment.

What are the side effects of TB-500?

Short answer: they are not established. We found no published human study of TB-500 itself. FDA says it “has not identified any human exposure data” for drug products containing the fragment and “lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans.” The risk FDA names is immunogenicity (an immune reaction) for certain routes of administration, because of possible aggregation and peptide-related impurities.[3]

The “thymosin beta-4 side effects” often quoted online come from studies of the full-length 43-amino-acid molecule, not TB-500: adverse events were “infrequent, and mild or moderate in intensity” in a 40-person intravenous study in healthy volunteers,[5] and a topical gel’s safety was “comparable to placebo” in 73 people with venous ulcers.[6] Both were small, short studies of a different molecule, so in our view they say little about an injected 7-amino-acid fragment. A 2026 Sports Medicine review of approved and unapproved peptides, which covers TB-500, says “rigorous human safety data are scarce.”[7]

What is not known

There are no published controlled human trials of TB-500 itself, no human pharmacokinetic data, and no established human dose. A 2026 review of gray-market sports peptides lists TB-500 among unapproved compounds with scarce human safety data.[7] An October 2026 review in an orthopaedic surgeons’ journal reached the same conclusion; see below.[9]

New, October 2026: what an orthopaedic surgeons’ journal concluded

The short answer: a review published October 27, 2026 in the Journal of the American Academy of Orthopaedic Surgeons (JAAOS) found no controlled human evidence that TB-500, thymosin beta-4 or BPC-157 helps musculoskeletal injuries. It also says TB-500 should not be treated as the same thing as thymosin beta-4. The authors conclude: “Routine clinical use cannot be currently recommended.”[9]

The narrative review is by Alexander Tham, Christopher W. Hodgkins and John G. Kennedy. PubMed lists their affiliations as the foot and ankle surgery division at NYU Langone Health and Baptist Health Orthopaedic Care in Florida. They searched PubMed/MEDLINE, EMBASE and Scopus from inception through June 2026, and also reviewed regulatory and antidoping sources. What the abstract says:[9]

• TB-500. It is “a distinct seven amino-acid fragment of TB-4 that is frequently conflated with full-length TB-4 despite the absence of validated biologic or clinical equivalence.” That matches what we found when we traced TB-500’s history in our TB-500 paper trail.[9]
• Thymosin beta-4. The full-length protein has more human experience, in eye, skin and heart studies, but its direct musculoskeletal evidence “remains limited to in vitro and rodent studies.” The authors add: “These nonorthopaedic findings cannot establish musculoskeletal efficacy or safety.”[9]
• BPC-157. It has the most direct musculoskeletal lab and animal evidence of the three, mostly in small animals. Human musculoskeletal evidence “is limited to one small retrospective uncontrolled case series without validated outcome measures,” and “validated dosing, pharmacokinetic, and long-term safety data are lacking.” More in our BPC-157 review.[9]
• Products. The authors flag concerns about the “identity, purity, concentration, sterility, and manufacturing consistency” of commercial products.[9]
• Bottom line for surgeons. None of the three has an FDA-approved musculoskeletal use, a validated orthopaedic treatment protocol, or controlled human orthopaedic efficacy evidence. The authors say orthopaedic clinicians should “specifically ask about peptide use” and counsel athletes about antidoping rules.[9]

Antidoping status. The World Anti-Doping Agency’s 2026 Prohibited List, in effect since January 1, 2026, names “Thymosin-ß4 and its derivatives e.g. TB-500” among growth factors (section S2.3), prohibited at all times, in and out of competition. It names BPC-157 under non-approved substances (section S0), also prohibited at all times.[10] Our analysis: the HHS draft compounding policy described above is about US pharmacy enforcement. As we read it, it does not change WADA’s list, which applies in sports that follow the World Anti-Doping Code.[8][10]

Limits. This is a narrative review, not a systematic review or new data, and its conclusions largely match what this page already said. We read the abstract through PubMed. The publisher’s full text was not available to us (it returned an error), so we could not check which studies the authors counted, which case series they mean, or their funding and disclosure statements. PubMed lists no conflict-of-interest statement for the paper.[9]

Our analysis: the news here is less the conclusion than the audience. A mainstream orthopaedic journal is telling surgeons to ask patients directly about these peptides, which suggests use has become common enough to come up in clinic (see the BPC-157 medical-records study). The same logic works the other way: if you have used TB-500 or similar products and are seeing a surgeon or doctor, telling them lets them factor it in. This page doesn’t recommend using, sourcing or dosing TB-500.

This page summarizes published research and regulatory documents. It is not medical advice and does not recommend using, sourcing, or dosing any of these substances.