TB-500 Compounding Pharmacy, FDA, and State Board Enforcement History

Is TB-500 an approved drug in any market FDA checked?

No. FDA's July 2026 review found no USP or National Formulary monograph for the substance, no FDA-approved drug containing it, no listing in the European or Japanese pharmacopeias, and no approved product in Canada, Australia, the UK, Belgium, Ireland, France, Norway, Germany, Spain or Italy, or authorised by the European Medicines Agency [1].

TB-500 is a synthetic 7-amino-acid fragment of thymosin beta-4, residues 17 to 23, N-acetylated, with a molecular weight of about 889 g/mol. It is not the full 43-amino-acid protein and not thymosin alpha-1 [1]. 'TB-500' is a common name rather than an official drug name, and FDA found several salts and derivatives, including different active moieties, sold under it [1]. According to FDA's review, TB-500 appears to have first been synthesized in 2003, and a veterinary preparation marketed to boost performance in horses and greyhounds appeared in 2011 [1]. The version sold online is a research-use-only injectable powder in 2 mg to 15 mg vials, alone or blended with BPC-157 [1].

Human studies of full-length thymosin beta-4, whether eye drops or intravenous recombinant protein, do not show that TB-500 works or is safe [1].

Does any FDA compounding list cover TB-500?

No. FDA's interim policy sorts nominated substances into three categories; category 1 is the one where FDA says it does not intend to act against a compounder that meets the policy conditions [4]. TB-500 appears in none of the three categories on FDA's list for state-licensed pharmacies and physicians, updated May 14, 2026, and in none of the categories on FDA's list for outsourcing facilities, updated March 21, 2025, so the category 1 policy does not cover it [2][3][4]. FDA also found no pharmacy marketing a compounded TB-500 product and no outsourcing facility reporting one [1].

Why it sits in the 'nominated but withdrawn' table

FDA's page on bulk substances that may present significant safety risks, with content dated 04/22/2026, lists 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' in the table of substances previously in category 2 whose nominators withdrew them [5]. FDA's stated concerns were that it 'has not identified any human exposure data' on drug products containing the fragment, that it lacks important information on the substance's safety, and that injectable peptides may pose immunogenicity risk from aggregation and peptide-related impurities [5]. Removal from category 2 was not a finding that TB-500 is safe [5].

July 2026: staff recommended against listing, advisers voted for it

FDA staff's briefing document proposed that neither TB-500 free base nor TB-500 acetate be added to the pharmacy list. The reasons given: the substance is not well characterized (inconsistent naming; no impurity, aggregate or endotoxin data), its historical use is unclear, there is no evidence of effectiveness for wound healing, the use FDA evaluated, there are no human data of any kind, injection carries immunogenicity risk, and FDA-approved wound treatments already exist [1].

The Pharmacy Compounding Advisory Committee took up TB-500 on July 23, 2026 and voted in favour of adding it, against the staff recommendation [6][7]. FDA generally follows advisory committee recommendations but is not legally bound to [6]. Adding a substance to the list takes formal rulemaking, and TB-500 is not on the list [7].

The October 2026 HHS draft policy

HHS filed a draft enforcement-discretion policy for compounding with certain peptides on October 28, 2026, Federal Register document 2026-22192, with publication scheduled for October 30, 2026 and comments due two weeks after publication [7][8]. It names six peptides, BPC-157, epitalon, KPV, MOTS-c, Semax and TB-500, and covers TB-500 acetate given by subcutaneous or intramuscular injection [7][8]. HHS says it 'does not intend to take enforcement action' against a state-licensed pharmacy, federal facility or licensed physician compounding with it where the policy conditions are met: 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].

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

What the safety record behind these decisions looks like

FDA searched PubMed, Embase, ClinicalTrials.gov and other sources and found no article in which TB-500 was given to a human; none of the three papers the nominator cited involved TB-500 in people [1]. An in-vitro scratch-wound test found that TB-500 at 50 micrograms/mL did not induce wound closure in fibroblast cultures, while a shorter metabolite, N-acetylated LKKTE, did show activity [1]. FDA found no nonclinical toxicity studies, no immunogenicity or aggregation studies, and no human pharmacokinetic or pharmacodynamic data by any route [1].

Its adverse-event database search through March 26, 2025 retrieved no TB-500 reports, and its food and supplement complaint system, covering January 1, 2004 to March 10, 2025, retrieved two cases about a blended TB-500 and BPC-157 product with no safety assessment [1]. FDA separately described a 40-year-old woman who used a research-purposes-only BPC-157 plus TB-500 (5 mg/5 mg) injection twice daily and developed widespread skin hyperpigmentation and gum darkening within a week, recurring when she retried the product two weeks later; because the product held two peptides, FDA said it could not tell whether either caused it [10].

There is no approved dose and no human dosing study; the nomination FDA reviewed proposed a 3 mg/mL lyophilized powder for subcutaneous or intramuscular injection [1].

Is TB-500 prohibited in sport?

Yes. WADA's Prohibited List names 'Thymosin-beta4 and its derivatives e.g. TB-500' under 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 appears 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][11]. A 2012 paper described the synthesis and characterization of the N-acetylated 17-23 fragment 'identified in TB-500, a product suspected to possess doping potential', and suggested detection methods for plasma and urine; it is analytical chemistry, not a clinical study [12].