TB-500 Legal Status, FDA 503A Category, and Compounding Access

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.