TB-500

What is TB-500, and is it the same as thymosin beta-4?

Thymosin beta-4 is a 43-amino-acid protein first isolated from calf thymus and later shown to be present in many cell types and released into body fluids such as blood, saliva, tears and wound fluid. It binds actin, the building block of the cytoskeleton. ^[1]

According to the FDA’s 2026 assessment, TB-500 is a seven-amino-acid synthetic peptide, N-terminally acetylated, corresponding to amino acids 17–23 of this protein (the LKKTETQ sequence); it was first derived from thymosin beta-4 in 2003. The FDA emphasizes that TB-500 is often promoted on the internet as “the synthetic version of thymosin beta-4” and that the two names are used interchangeably, but that they are not the same substance. ^[1]

This distinction matters: most laboratory and animal studies and all human studies have been done with full-length thymosin beta-4. The FDA also states that an acetyl group can change a peptide’s charge, size and binding properties, so findings obtained with the non-acetylated LKKTETQ sequence cannot be transferred directly to acetylated TB-500. ^[1]

What do animal and laboratory studies show?

The table below shows which molecule was examined in which model.

The FDA’s conclusion is clear: preclinical pharmacological evidence showing that TB-500 supports wound healing is currently lacking, and there is no toxicity study for TB-500 that could serve for a safety assessment. ^[1] For none of the uses put forward on the internet for TB-500, such as muscle growth, endurance, hair growth and heart health (which the FDA compiled one by one from websites), is there a human study done with TB-500. ^[1]

Has TB-500 been tried in humans?

No. The FDA states that it found no article, clinical study or human exposure data in which TB-500 was administered to humans, and that the possible safety risks of TB-500 in humans are therefore unknown. In FAERS, the FDA’s adverse event database, there were no reports for TB-500 through March 2025, and in the food and supplement complaint system two case records related to a “mixture of TB-500 and BPC-157,” without a safety assessment, emerged. ^[1]

In the BPC-157 assessment, widespread darkening of the skin and gums was reported in a woman using a mixture containing BPC-157 and TB-500 labeled “for research purposes only”; the picture recurred when the product was restarted, but the shares of the two peptides could not be distinguished. ^[13]

What did the thymosin beta-4 eye drop trials find?

The area in which thymosin beta-4 has been most studied in humans is the eye drop code-named RGN-259. These studies were done not with TB-500 but with the full-length protein, and their results cannot be transferred to TB-500 used by injection.

• Dry eye, phase 2 (72 people): In the randomized, placebo-controlled trial of 72 people with moderate-to-severe dry eye, the two primary outcomes (ocular discomfort and inferior corneal staining) were not found to differ from placebo on day 29; significant differences in some secondary outcomes were reported, and no adverse effects were seen. ^[4]
• Dry eye, phase 3 ARISE-2 and ARISE-3: According to the results records on ClinicalTrials.gov, 601 people took part in ARISE-2 and 700 in ARISE-3. ^[5] In ARISE-3, the change in inferior corneal staining on day 15 was −0.41 in the drug group and −0.46 in the placebo group; the change in ocular discomfort was −0.4 points in both groups. The record contains no statistical analysis. ^[6]
• Neurotrophic keratopathy, phase 3 (18 people): In patients with persistent corneal surface damage, complete healing at the end of 4 weeks was seen in 6 of 10 people in the RGN-259 group and in 1 of 8 in the placebo group (p=0.0656; not statistically significant). Improvement in some secondary measures and discomfort symptoms was reported. The trial was funded by the company that developed the drug; two of the authors are employees of this company and one of the parent company, and the trial was designed by company employees and the first author. ^[7]

These results show that even in thymosin beta-4’s most advanced human program, a consistent benefit could not be demonstrated. According to the FDA, there is no TB-500 product approved by the EMA in the EU, and there is no approved TB-500 product in Canada, Australia, the United Kingdom and various EU countries. ^[1]

Are there other human studies of thymosin beta-4?

Outside the eye, full thymosin beta-4 has also been tried in skin ulcers. A review written by researchers who have long worked on thymosin beta-4 (the authors include two of the authors of the 1999 rat study) reports that in two phase 2 trials in venous stasis and pressure ulcers, thymosin beta-4 accelerated healing by about a month in patients who healed. ^[14] This statement describes only the time in patients who healed; it does not show whether there was a difference in the proportion of patients who healed. These trials too were done not with TB-500 but with the full-length protein.

Why is TB-500 so well known?

A study cited by the FDA examined doping discussions on 13 internet forums; it found that discussions about peptides and growth factors have increased since 2001, that TB-500 came onto the agenda after 2010, and that it was one of the two substances most frequently mentioned by “brand name.” ^[1] The FDA also writes that it came across websites selling powder products in various amounts stated to be for research purposes, giving usage instructions or offering consultation appointments for TB-500. ^[1] Visibility on the internet is not related to the strength of the evidence: the same FDA assessment found no human data for any of these uses.

Is TB-500 banned in sport? Doping cases

WADA’s 2026 Prohibited List names “thymosin-β4 and its derivatives, e.g., TB-500” under S2.3 “growth factors and growth factor modulators”; substances in class S2 are prohibited at all times, in and out of competition. ^[8] According to the FDA’s account, WADA approved in 2013 a research project aimed at detecting the breakdown products of TB-500; the veterinary preparation of TB-500 was marketed in 2011 as performance-enhancing in horse and greyhound racing. ^[1]

The best-known case is in Australia. According to WADA’s statement, after the Australian Crime Commission’s February 2013 report alleging widespread doping in sport, the Australian Sports Anti-Doping Authority brought proceedings against players who played for the Essendon Football Club in the 2012 season, on the charge of using the prohibited peptide thymosin beta-4. The AFL tribunal cleared the players in 2015; on WADA’s appeal, the Court of Arbitration for Sport (CAS) imposed two-year bans on 34 former and current players on 11 January 2016. ^[9] This case concerns thymosin beta-4, not TB-500; on the WADA list, however, both are prohibited under the same heading.

What is the status of TB-500 in the USA?

In the archived copy of the September 27, 2024 version of the FDA page, “thymosin beta-4 fragment (LKKTETQ)” appears in the 503A category 2 table, reserved for substances that may present significant safety risks, with an addition date of 29 September 2023. ^[15] In the FDA’s page dated April 22, 2026, “thymosin beta-4 fragment (LKKTETQ), also known as TB-500” has been moved to the table of substances formerly in category 2 whose nominations were withdrawn by the nominators. The FDA’s rationale on this row: risk of immune response owing to aggregation and peptide impurities with some routes of administration, and the absence of any human exposure data for products containing TB-500. ^[2]

In its report prepared for the July 2026 advisory committee, FDA staff recommended that TB-500 not be added to the list of substances that pharmacies can use in compounding. ^[1] On 23 July 2026, the committee (PCAC) advised that TB-500, together with BPC-157, be added to the list. According to a law firm summarizing the meeting, the vote ended 8 yes, 6 no, 1 abstention, and for these recommendations to take effect, the FDA must conduct a rulemaking process with public comment. ^[10] The recommendation is not binding. This process is not a drug approval.

What is the status of TB-500 in Türkiye?

Status in Türkiye

License

No product containing TB-500 or thymosin beta-4 in the Licensed Human Medicinal Products List of TİTCK (Turkish Medicines and Medical Devices Agency) dated October 16, 2026 ^[12]

Law

Law No. 1262 on Pharmaceutical and Medicinal Preparations (İspençiyari ve Tıbbi Müstahzarlar Kanunu) ^[11]

Sport

WADA S2.3: prohibited at all times ^[8]

Article 3 of Law No. 1262 makes the placing of preparations on the market and their import subject to Ministry permission. Article 19 provides imprisonment of one to five years for those who manufacture unlicensed preparations and those who knowingly sell or offer them for sale, considers the commercial import of a preparation made abroad without a license to be smuggling, and provides for access blocking in promotion or sale over the internet. ^[11] How products labeled “for research purposes” stand in relation to these provisions is assessed in each concrete case by the administration and the courts; this page is not legal advice.

For the general framework: Are peptides legal? and What does research peptide mean?

What are the risks of TB-500?

The risk picture for TB-500 consists more of unknowns than of known adverse effects:

• No toxicity data: The FDA found no preclinical toxicity study for TB-500; genetic damage, reproductive and carcinogenicity tests have not been done. ^[1]
• Immune response: According to the FDA, peptides given by injection can produce an immune response; outcomes range from asymptomatic antibodies to severe reactions and cannot be predicted in advance. There is no study examining this risk for TB-500. ^[1]
• Naming and content uncertainty: TB-500 is not an official drug name; the FDA states that different salts and derivatives are sold under the same common name, and that some sellers use the identification number given for the free base for the acetate salt. ^[1]
• Blood vessel formation: Full thymosin beta-4 increased blood vessel formation in an animal wound model. ^[3] The meaning of this effect for tumor development has not been examined in humans.
• Mixed products: TB-500 is often sold in the same vial as BPC-157; when an adverse effect develops, it cannot be distinguished which substance it is attributable to. ^[13]

The adverse effect and product quality information gathered for BPC-157 is also instructive for TB-500, because the two substances are sold through the same channels:

Detailed guideBPC-157 side effects: what is known, what is unknown?→ Detailed guideBPC-157: evidence, risks and legal status→

For the copper peptide also used as a cosmetic ingredient: GHK-Cu.

Limits of this guide

This page summarizes published evidence and official documents on TB-500 and thymosin beta-4. It contains no dose, preparation, administration, course or product source; conditions in animal studies are not transferred to humans. Because TB-500 has never been studied in humans, no safe manner of use has been defined. The regulatory situation is changing rapidly; the information on this page is valid as of October 2026.

Are there other human studies of full-length thymosin beta-4?

Yes. A 2010 randomized, placebo-controlled early-phase study by Ruff and colleagues assessed intravenous full-length thymosin beta-4 safety and pharmacokinetics in 40 healthy volunteers. It does not establish efficacy of the TB-500 fragment or treatment of sports injuries. Describing human research as limited to eye drops was incorrect. ^[16]

Correction — 19 October 2026

The statement that human studies of full-length thymosin beta-4 were limited to eye drops was corrected; the distinction from the fragment is retained.