# TB-500 Legal Status, FDA 503A Category, and Compounding Access > TB-500 legal status: FDA placed Thymosin beta-4, fragment (LKKTETQ), also known as TB-500, in 503A Category 2 (2023). It is not FDA-approved and is WADA-prohibited. Access under active FDA review. The present-tense regulatory record — FDA non-approval, the 503A Category 2 placement, an active 2026 review, and WADA prohibition — set as a canon of standing, every fact cited to the FDA. ## The standing of TB-500 today TB-500 legal status, stated in the present tense and sealed to the FDA, is this. The FDA lists the substance as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" and has placed it in 503A "Category 2" — bulk drug substances that may present significant safety risks — effective with the FDA's September 29, 2023 update to its nominated-substances list, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information [16]. As a Category 2 substance it is not within the FDA's enforcement-discretion policy for 503A compounding, and it is not an FDA-approved drug [16]. The FDA's own list entry establishes the relationship between the two names: TB-500 is the LKKTETQ fragment associated with thymosin beta-4. This is the canon entry from which the rest of this page reads. It is general information about the regulatory landscape — not medical or legal advice, and not an offer to sell or supply any substance. ## Access is under active FDA review and may expand in 2026 The forward-leaning fact, stated with care, is that this standing is not frozen. "TB-500 (free base)" and "TB-500 acetate" appear individually on the published agenda of the FDA Pharmacy Compounding Advisory Committee (PCAC) meeting scheduled for July 23-24, 2026, as bulk drug substances "being considered for inclusion on the 503A Bulks List" — the same agenda that also lists BPC-157, KPV, and MOTs-C [17]. The substance is, in other words, under active evaluation, and access could expand. The equally important fact is what that agenda is not. A PCAC discussion is a scheduled evaluation only. It is advisory, not a final FDA decision; it is not a reclassification, not a listing, and not a change in current status. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by PCAC, and being discussed by the committee is a step in evaluation, not the outcome [18]. No result of the July 2026 meeting should be assumed or dated. This codex states the momentum and refuses to state the verdict. ## Is TB-500 FDA Approved? No. TB-500 is not an FDA-approved drug and has no FDA-approved therapeutic indication [16]. FDA approval of a finished drug, through a New Drug Application or Biologics License Application, is a separate question from whether a bulk substance may be used in compounding [18]. TB-500 satisfies neither: it is not an approved medicine, and as a Category 2 bulk substance it is not within the enforcement-discretion policy for 503A compounding while that status stands [16]. The substance is supplied by research suppliers for laboratory use, not as an approved therapeutic. ## How the 503A and 503B compounding framework works Under the Federal Food, Drug, and Cosmetic Act, compounding runs through two sections [18]. Section 503A covers traditional, patient-specific compounding by state-licensed pharmacies and physicians, generally pursuant to a valid prescription for an individual patient. Section 503B covers registered outsourcing facilities that compound larger batches under cGMP-style oversight and FDA registration and inspection. A compounder may use a bulk drug substance — an active ingredient used as a starting material, rather than an FDA-approved finished drug — only if that substance has an applicable USP/NF monograph, is a component of an FDA-approved drug, or appears on the relevant FDA bulks list [18]. Substances not yet on a bulks list are evaluated by the FDA through a public nomination process with input from PCAC. The FDA's interim policy sorted nominated substances into Category 1 (covered by enforcement discretion while under evaluation) and Category 2 (identified as raising significant safety risks, and not covered by that discretion) [18]. TB-500 sits in Category 2 [16]. ## Can You Get TB-500 From a Compounding Pharmacy? Compounding-pharmacy access for this peptide is constrained by the bulk-substance rules above. In general terms, a legally compounded medication is prepared only after an individual patient is evaluated by an appropriately licensed prescriber — in person or through a compliant telehealth encounter — who determines a compounded preparation is clinically appropriate and issues a valid, patient-specific prescription [18]. The preparation is then made by a state-licensed 503A compounding pharmacy or, for office or batch use, sourced from an FDA-registered 503B outsourcing facility. Telehealth is one channel for that prescriber-evaluation step. It is a route to a licensed-prescriber consultation and prescription, not a separate legal status: it does not expand which substances may be compounded and does not remove the need for a legitimate clinical evaluation and a valid prescription [18]. The decisive constraint is ingredient eligibility — a compounder may use an active ingredient only if it is eligible under the 503A/503B rules, and a substance the FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [18]. For TB-500, that Category 2 status is the operative fact today [16]. This is general information about the lawful pathway, not guidance on obtaining any restricted substance, and it names no pharmacy, clinic, telehealth provider, or vendor. ## Is TB-500 banned by WADA and in competitive sports? Yes. TB-500 and thymosin beta-4 fall under the World Anti-Doping Agency's prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition for the relevant classes. The substance is detected by LC-MS anti-doping assays in equine and human matrices. The first rigorous chemical characterization of the Ac-17-23 fragment was itself published as a doping-control reference for a product "suspected to possess doping potential" [9], which is how the analytical world first fixed TB-500's identity. ## Why is TB-500 used in racehorses? TB-500 was encountered as a designer peptide in equine sport, which prompted the development of LC-MS detection methods for the fragment and its metabolites in horses [9]. It is supplied as a veterinary-context preparation of the synthetic Ac-LKKTETQ fragment and is treated as a doping-control target, not as an approved equine therapeutic. Its presence in racing is a matter for anti-doping enforcement, not evidence of an approved indication. --- A gothic research codex of the thymosin beta-4 record — inscribed from the literature, sealed to its sources, and dispensing nothing.