TB-500 Regulatory Status: US, EU, Canada, and UK

What is TB-500?

TB-500 is a synthetic 7-amino-acid fragment of the 43-amino-acid protein thymosin beta-4. It is N-acetylated, covers residues 17 to 23, and has a molecular weight of about 889 g/mol [1]. It is not full-length thymosin beta-4 and not thymosin alpha-1 [1]. The name TB-500 is a common name, not an official drug name; FDA found several salts and derivatives, including different active moieties, sold under the same name [1].

Human studies of full-length thymosin beta-4, including eye-drop and intravenous recombinant products, do not show that TB-500 works or is safe [1]. FDA found no article in which TB-500 itself was given to a human, and none of the three papers the nominator cited involved TB-500 in humans [1].

Is TB-500 approved in the United States?

No. TB-500 is not an FDA-approved drug [1]. FDA's July 2026 review found no USP or National Formulary monograph for it, no FDA-approved drug containing it, no listing in the European or Japanese pharmacopeias, and no pharmacy marketing a compounded TB-500 product; no outsourcing facility reported one [1].

In the United States, FDA has evaluated whether TB-500 may be used as a bulk substance in compounded drugs. TB-500 appears in none of the three categories on FDA's list for state-licensed pharmacies and physicians, updated May 14, 2026, or on FDA's list for outsourcing facilities, updated March 21, 2025 [2][3][4]. FDA's policy of generally not taking action against compounders who meet set conditions does not cover it [2][3][4].

FDA's safety-risk page for bulk substances nominated for compounding, with content dated 04/22/2026, lists 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' in its nominated-but-withdrawn table [5]. That table holds substances previously in FDA's significant-safety-risk category whose nominators withdrew them; TB-500 is not in the active table [5]. Removal from that category was not a finding that TB-500 is safe [5]. FDA's stated concerns were that it had not identified any human exposure data on drug products containing the fragment, lacked important safety information, and that injectable peptides may pose immunogenicity risk because of aggregation and peptide-related impurities [5].

In July 2026, FDA staff proposed that neither TB-500 free base nor TB-500 acetate be added to the compounding bulks list [1]. The staff briefing document cited inconsistent naming, no impurity, aggregate or endotoxin data, unclear historical use, no evidence of effectiveness for wound healing (the use FDA evaluated), no human data of any kind, immunogenicity risk for injection, and the existence of FDA-approved wound treatments [1].

The Pharmacy Compounding Advisory Committee reviewed TB-500 on July 23, 2026 and voted in favor of adding it to the bulks list, against FDA staff's recommendation [6][7]. That vote is advice only and is not binding [6][7]. TB-500 is not on the list; adding it takes formal rulemaking [7].

HHS has also issued a draft enforcement-discretion policy for compounding with certain peptides, filed October 28, 2026 as Federal Register document 2026-22192, with publication scheduled October 30, 2026 and comments due two weeks after publication [7]. The draft names TB-500 among six peptides, covers TB-500 acetate for subcutaneous or intramuscular injection, and says HHS 'does not intend to take enforcement action' against a state-licensed pharmacy, federal facility or licensed physician compounding with it if conditions are met, such as a single active ingredient, a patient-specific prescription, an FDA-registered manufacturer with a certificate of analysis, and a label reading 'This is a compounded drug product. Not for resale.' [7][8].

That draft is not an FDA approval and does not put TB-500 on any list [7]. The notice says it 'does not establish any rights for any person and is not binding on HHS or the public,' and HHS may revisit it if a safety signal or product quality issue arises [7]. Compounded drugs are not FDA-approved: FDA does not review their safety, effectiveness or quality before marketing [7].

Is TB-500 approved in the European Union?

No. The European Medicines Agency has not authorized a TB-500 product [1]. FDA's review found no approved product in Belgium, Ireland, France, Norway, Germany, Spain or Italy [1]. It also found no listing in the European pharmacopeias [1].

Is TB-500 approved in Canada?

No. FDA's review found no approved product containing TB-500 in Canada [1].

Is TB-500 approved in the United Kingdom?

No. FDA's review found no approved product containing TB-500 in the UK [1].

Is TB-500 banned in sport?

Yes, for athletes under the World Anti-Doping Code. WADA's Prohibited List names 'Thymosin-beta4 and its derivatives e.g. TB-500' in S2.3, growth factors and growth factor modulators [9]. It is prohibited at all times, in and out of competition, and S2 substances are non-Specified Substances [9]. It is on the 2026 List, in force since January 1, 2026, and stays on the 2027 List in the tracked-changes version dated 26 August 2026 [9][10].

Is there an approved TB-500 dose?

No approved dose exists [1]. The nomination FDA reviewed proposed a 3 mg/mL lyophilized powder for subcutaneous or intramuscular injection, but that was a proposal, not an approved dose [1]. The product sold online as 'research use only' is not an approved medicine in the US, EU, Canada or UK [1].