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

The current FDA standing, stated first

TB-500 legal status, as it stands today: TB-500 — which FDA lists as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" — is a research peptide that FDA placed in 503A "Category 2" (bulk substances that may present significant safety risks), effective with FDA's September 29, 2023 update to its list of nominated bulk drug substances, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information ^[13]. As a Category 2 substance it is not within FDA's enforcement-discretion policy for 503A compounding, and it is not an FDA-approved drug ^[13].

FDA's own list entry establishes the identity relationship this site keeps reconciling: TB-500 is the LKKTETQ fragment associated with thymosin beta-4, and FDA describes the two together in the same entry ^[13]. This page is general information about the regulatory landscape — not medical or legal advice, and not an offer to sell or supply any substance.

Under active review: the July 2026 PCAC agenda

Access to TB-500 through compounding is under active FDA review and may expand in 2026 — but nothing has changed yet, and the current flag still stands. The forward-leaning fact is concrete and citable: "TB-500 (free base)" / "TB-500 acetate" are individually named 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" ^[14]. The same agenda lists BPC-157, KPV and MOTs-C ^[14].

What that is, precisely: a scheduled evaluation and discussion. What it is not: a listing decision, a reclassification, or any change in current status ^[14]. 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 a final listing ^[15]. A PCAC discussion is advisory, and its outcome is unknown — no result should be assumed or dated.

What the 503A and 503B framework means

Under the Federal Food, Drug, and Cosmetic Act, drug compounding runs through two sections. Section 503A covers traditional, patient-specific compounding by state-licensed pharmacies and physicians, generally pursuant to a valid prescription for an individual patient ^[15]. Section 503B covers FDA-registered "outsourcing facilities" that may compound larger batches under cGMP-style oversight ^[15].

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 ^[15]. Category 1 substances are those FDA judged may be eligible for the list and that do not raise significant safety risks; FDA does not intend to act against compounding with them while it evaluates ^[15]. Category 2 substances — TB-500's category — are those FDA identified as raising significant safety risks, and they are not covered by that enforcement-discretion policy ^[13]. FDA approval of a finished drug is a separate question from whether a bulk substance may be used in compounding; TB-500 is neither an approved drug nor afforded Category 1 discretion ^[13][15].

How legally compounded access works

In general terms, a legally compounded medication is prepared only after an individual patient is evaluated by an appropriately licensed prescriber who determines a compounded preparation is clinically appropriate and issues a valid, patient-specific prescription ^[15]. The preparation is then made by a state-licensed 503A compounding pharmacy (patient-specific) or, for larger volumes, sourced from an FDA-registered 503B outsourcing facility ^[15].

Telehealth can serve as the front-end channel through which a patient is evaluated and a prescription is issued, but it does not change which substances are eligible to be compounded, and it does not remove the need for a legitimate prescriber–patient relationship and a valid prescription ^[15]. The decisive caveat is the ingredient itself: a compounder may use a requested active ingredient only if it is eligible under the 503A/503B bulk-substance rules, and a Category 2 substance that FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands ^[13][15]. This is a description of the lawful pathway in general terms, with no specific pharmacy, clinic, telehealth provider or vendor named, and no dosing or administration guidance.

Is TB-500 banned by WADA and in competitive sports?

Yes. TB-500 and thymosin beta-4 are prohibited by the World Anti-Doping Agency under prohibited peptide/growth-factor and tissue-repair categories, banned in and out of competition for the relevant classes ^[16]. They are detectable by LC-MS anti-doping assays in equine and human matrices ^[16]. TB-500 has been encountered as a designer substance in racehorses, which prompted the equine and human detection methods now in use ^[16].

Is TB-500 FDA Approved?

No. TB-500 has no FDA-approved therapeutic indication; it is not an FDA-approved drug ^[13]. FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 as a bulk substance that may present significant safety risks, citing concerns including potential immunogenicity for certain routes and a lack of important safety information ^[13]. FDA approval of a finished drug and eligibility of a bulk substance for compounding are separate questions, and TB-500 satisfies neither ^[13][15].

Is TB-500 legal?

The accurate answer is a status, not a yes or no. TB-500 is not an FDA-approved drug, and FDA placed it in 503A Category 2 — a flag that means it is not within FDA's enforcement-discretion policy for routine 503A compounding ^[13]. It is prohibited in sport by WADA ^[16]. This page states the present-tense, FDA-citable regulatory standing as general information, not legal advice, and not an offer to supply anything ^[13].

Can you get TB-500 from a compounding pharmacy?

Not through routine 503A compounding while its current FDA status stands. A compounder may use a bulk substance only if it is eligible under the 503A/503B rules, and TB-500's Category 2 placement means FDA identified it as a significant-safety-risk substance not afforded enforcement discretion ^[13][15]. Lawful compounded access in general requires a licensed-prescriber evaluation and a valid patient-specific prescription, but the ingredient-eligibility caveat applies regardless of the prescription ^[15].

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 its September 29, 2023 nominated-substances update, citing potential immunogenicity for certain routes and a lack of important safety information ^[13]. Category 2 substances are not covered by FDA's enforcement-discretion policy for 503A compounding ^[13]. TB-500 is also individually named on the July 23–24, 2026 PCAC agenda as a substance being considered for the bulks list — a scheduled discussion, not a decision ^[14].