TB-500 legal status, FDA 503A category, and compounding access

TB-500 legal status: the current FDA fact

TB-500 legal status starts with one citable FDA fact. FDA lists this substance as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500," and placed it in 503A "Category 2" — bulk substances that may present significant safety risks — effective with FDA's September 29, 2023 update to the list of bulk drug substances nominated for use under section 503A ^[16]. FDA's stated rationale for the placement includes concerns about potential immunogenicity for certain routes of administration and a lack of important safety information ^[16]. As a Category 2 substance, TB-500 is not within FDA's enforcement-discretion policy for 503A compounding, and it is not an FDA-approved drug ^[16][17]. FDA's own list entry establishes the identity link this whole site turns on: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 ^[16].

A short framework note makes the category legible. Under the Federal Food, Drug, and Cosmetic Act, section 503A covers traditional, patient-specific compounding by state-licensed pharmacies and physicians, and section 503B covers FDA-registered outsourcing facilities compounding larger batches under cGMP-style oversight ^[17]. A compounder may use a bulk drug substance only if it has an applicable USP/NF monograph, is a component of an FDA-approved drug, or appears on the relevant FDA bulks list; substances not yet listed are evaluated by FDA through a public nomination process informed by the Pharmacy Compounding Advisory Committee (PCAC) ^[17]. Category 2 is FDA's flag that a nominated substance raises significant safety risks and is not afforded the enforcement discretion that applies to Category 1 ^[17].

Access is under active FDA review and may expand in 2026

The forward-looking fact is real and it is on FDA's own calendar. "TB-500 (free base)" and "TB-500 acetate" appear on the published agenda of the FDA Pharmacy Compounding Advisory Committee meeting scheduled for July 23-24, 2026, as bulk drug substances "being considered for inclusion on the 503A Bulks List" — the same agenda also lists BPC-157, KPV, and MOTs-C ^[18]. That places TB-500 squarely under active evaluation, and it is the honest basis for saying its compounding access may expand.

It is just as important to state precisely what that meeting is not. A scheduled PCAC discussion is an advisory evaluation, not a listing decision, not a reclassification, and not a change in current status ^[18]. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by PCAC; being discussed by the committee is a step in evaluation, not an outcome ^[17]. The outcome of the July 2026 meeting is unknown, and nothing on this page assumes, dates, or asserts a result. As of FDA's last confirmable action, TB-500 remains in Category 2 ^[16].

What the current status does and does not mean

Two distinctions keep this accurate. First, FDA approval of a finished drug (a New Drug Application or Biologics License Application) is a separate question from whether a bulk substance may be used in compounding — and TB-500 is neither an approved drug nor a substance afforded compounding enforcement discretion ^[17]. Second, a Category 2 placement is a present-tense regulatory status, not a permanent verdict; FDA continues to evaluate nominated substances, which is exactly why the July 2026 PCAC discussion is on the calendar ^[16][18].

This page deliberately excludes claims that could not be confirmed from an authoritative FDA source. Reports that a group of Category 2 peptides was expected to move back toward Category 1 in early 2026, and vendor claims of specific dated removals of certain peptides from Category 2, could not be verified as completed, effective FDA actions and are not stated here as fact ^[16]. The status above is the last FDA action confirmable on FDA.gov.

How lawful compounded access actually works

In general terms, a legally compounded medication in the U.S. is prepared only after an individual patient is evaluated by an appropriately licensed prescriber who determines that a compounded preparation is clinically appropriate and issues a valid, patient-specific prescription ^[17]. The preparation is then made by a state-licensed 503A compounding pharmacy (patient-specific) or, for office or batch use, sourced from an FDA-registered 503B outsourcing facility ^[17]. Telehealth can serve as the front-end channel for that prescriber evaluation, but it does not change which substances are eligible to be compounded and does not remove the need for a legitimate clinical evaluation and a valid prescription ^[17].

The ingredient-eligibility caveat is the operative constraint here. A compounder may use a requested active ingredient only if that ingredient is eligible under the 503A/503B bulk-substance rules, and an ingredient FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands ^[17]. For TB-500, that is the present situation: a Category 2 flag means the substance is not within the routine 503A enforcement-discretion pathway today, regardless of the access mechanics described above ^[16][17]. This page names no pharmacy, clinic, telehealth provider, or vendor, gives no dosing, and describes only the lawful pathway in general terms.

Is TB-500 FDA approved?

No. TB-500 has no FDA-approved therapeutic indication; FDA lists it as the "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" bulk substance placed in 503A Category 2 ^[16]. It is sold by research suppliers for laboratory use only and is not an approved medicine ^[16]. FDA approval of a finished drug is a separate question from compounding eligibility, and TB-500 meets neither bar ^[17].

Is TB-500 legal?

TB-500 is not an FDA-approved drug and, as a 503A Category 2 substance, is not within FDA's enforcement-discretion policy for routine compounding ^[16][17]. It is sold by research suppliers for laboratory use only, it is prohibited in sport by WADA, and it is treated as a prescription medicine in some jurisdictions. This is general regulatory information, not legal advice — the precise rules depend on jurisdiction and route, and the FDA status above is the citable U.S. anchor ^[16].

Can you get TB-500 from a compounding pharmacy?

Under current FDA status, no — for routine 503A compounding. TB-500 is in Category 2, meaning FDA has flagged it for significant safety risks and it is not afforded the enforcement discretion that lets a 503A pharmacy compound with a permitted bulk substance ^[16][17]. Lawful compounded access generally runs through a licensed-prescriber evaluation, a valid patient-specific prescription, and a 503A pharmacy or 503B facility — but only when the ingredient is eligible, which TB-500 is not while its Category 2 flag stands ^[17].

What is the FDA 503A status of TB-500?

FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 — bulk substances that may present significant safety risks — effective with the September 29, 2023 nominated-substances update, citing potential immunogenicity for certain routes and a lack of important safety information ^[16]. Category 2 substances are not within FDA's enforcement-discretion policy for 503A compounding ^[17]. TB-500 is also on the agenda of the July 23-24, 2026 PCAC meeting as a substance being considered for the 503A bulks list — a scheduled discussion, not a decision ^[18].

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 ^[15]. They are detectable by LC-MS anti-doping assays in equine and human matrices — the WADA prohibited status is part of why detection methods were developed for the substance in the first place.

Why is TB-500 used in racehorses?

TB-500 has been encountered as a veterinary or designer preparation in equine sport, which prompted the development of the first LC-MS detection method in horse plasma and urine (limit of detection roughly 0.01-0.02 ng/mL) to control its misuse. Its appearance in racehorses is an anti-doping concern, not an approved indication — it is part of the same prohibited-substance picture that makes it WADA-banned in human sport ^[15].