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

The current FDA fact: TB-500's nomination was withdrawn and it is no longer in Category 2

The TB-500 legal status begins with one present-tense FDA fact. 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," the designation for bulk substances that may present significant safety risks ^[17]. The placement became effective with FDA's September 29, 2023 update to the list of bulk drug substances nominated for use under section 503A, and FDA cited concerns including potential immunogenicity for certain routes of administration and a lack of important safety information ^[17].

Two consequences follow directly from that status. First, that classification is no longer current: FDA's page dated April 22, 2026 shows TB-500 under "Bulk drug substances nominated but withdrawn" because its sponsor took back the nomination, and FDA has not explained what that withdrawal permits a 503A pharmacy to do ^[17]. Second, TB-500 is not an FDA-approved drug; it has no approved therapeutic indication ^[17]. FDA's own list entry establishes the identity relationship this whole site turns on: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 ^[17]. This is the last FDA action on the substance that is confirmable from FDA.gov, and it is the status as it stands.

Access went before FDA review in July 2026; no outcome yet

The second fact is concrete and hedged. TB-500 — listed as "TB-500 (free base)" and "TB-500 acetate" — was individually named on the published agenda of the FDA Pharmacy Compounding Advisory Committee (PCAC) meeting held July 23–24, 2026, as a bulk drug substance "being considered for inclusion on the 503A Bulks List" ^[18]. The same agenda also listed BPC-157, KPV, and MOTs-C ^[18]. Being named for discussion put its 503A eligibility in front of the committee, and FDA staff had proposed against adding it.

This is process, not a decision. A PCAC meeting is an evaluation and discussion step, not a listing decision and not, by itself, a change in status ^[18]. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by the committee; being on the agenda was a step in that process, and as of September 2026 FDA has published no record of the committee's votes ^[18]. FDA now shows TB-500's nomination as withdrawn and no longer in Category 2, but that change alone does not place it on the 503A Bulks List ^[17]. Some commercial sources have circulated claims of an early-2026 reclassification or a dated removal of certain peptides from Category 2; those reports could not be confirmed from an authoritative FDA source and are not treated as fact on this page ^[18]. The verifiable, present-tense position is: nomination withdrawn and off FDA's Category 2 table, discussed at the July 2026 meeting, and no outcome published or assumed.

Is TB-500 FDA approved?

The direct question — is TB-500 FDA approved — has a one-word answer: no. TB-500 has no FDA-approved therapeutic indication and is not an FDA-approved drug ^[17]. It is handled as a research chemical and appears in a veterinary and anti-doping context rather than as an approved human medicine ^[17].

Approval and compounding eligibility are separate questions. Whether FDA has approved a finished drug (through a New Drug Application or Biologics License Application) is distinct from whether a bulk substance may be used in compounding ^[17]. FDA now shows TB-500's nomination as withdrawn and the peptide no longer in Category 2, but the agency has not stated whether that entry changes what a 503A pharmacy may prepare ^[17]. The July 2026 PCAC discussion concerned the compounding-eligibility question only, and did not touch the approval status ^[18].

How legally compounded peptide access works

U.S. drug compounding runs through two sections of the Federal Food, Drug, and Cosmetic Act. Section 503A covers traditional, patient-specific compounding by state-licensed pharmacies and physicians, made pursuant to a valid prescription for an individual patient. Section 503B covers FDA-registered outsourcing facilities that compound larger batches under cGMP-style oversight ^[19]. 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 through a public nomination process with PCAC input ^[19].

The lawful pathway, in general terms: an appropriately licensed prescriber evaluates an individual patient — in person or through a compliant telehealth encounter — and determines whether a compounded preparation is clinically appropriate; if so, the prescriber issues a valid, patient-specific prescription; the prescription is dispensed by a state-licensed 503A pharmacy or, for office or batch use, sourced from a 503B outsourcing facility ^[19]. Telehealth is one front-end channel for that prescriber evaluation; it does not expand which substances may be compounded and does not remove the need for a legitimate clinical evaluation and a valid prescription ^[19]. The decisive caveat for this compound: a compounder may use an ingredient only if it is eligible under the bulk-substance rules, and FDA has not said how those rules treat a substance whose Category 2 nomination was withdrawn ^[17][19]. This is the FDA 503A compounding access picture for TB-500 — described here as general regulatory information, not as a route to obtain anything.

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

Yes. TB-500 falls under the World Anti-Doping Agency's prohibited peptide, growth-factor, and tissue-repair categories, and it is detected by liquid-chromatography–mass-spectrometry anti-doping assays ^[10]. It is banned in and out of competition for the relevant athlete classes.

The forensic interest has a specific origin: TB-500 was encountered as a designer tissue-repair drug in racehorses, which prompted the development of equine LC-MS detection methods ^[10]. That veterinary-doping history is also why the analytical literature characterizes the fragment and its metabolites — to detect it in plasma and urine, the same reason the substance is a known quantity in anti-doping science ^[10]. WADA prohibition is independent of the FDA compounding question; both stand at once.

Is TB-500 legal?

TB-500 remains an unapproved drug; FDA placed it in Category 2 with its September 29, 2023 update, but the agency's current page records that the nomination was withdrawn and has not said how 503A pharmacies should read its absence from Category 2 ^[17]. It is sold by suppliers for laboratory research use, it is WADA-prohibited in sport ^[10], and it was on the July 2026 FDA compounding-review agenda, where FDA staff had proposed against listing it; the agency has not published what the committee decided ^[18]. This is general information, not legal advice.

Can you get TB-500 from a compounding pharmacy?

FDA has not given pharmacies a clear answer. FDA now records TB-500's nomination as withdrawn and the peptide no longer in Category 2; the agency has not answered whether a 503A pharmacy can treat that change as permission to compound it ^[17][19]. The lawful framework runs through a licensed-prescriber evaluation and a patient-specific prescription, but whether TB-500 meets the ingredient-eligibility rule at all is the part FDA has not addressed ^[19].

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 ^[17]. Category 2 substances are not covered by FDA's enforcement-discretion policy for 503A compounding, but FDA's page, current as of April 22, 2026, no longer lists TB-500 in that category — its nomination shows as withdrawn, and FDA has not said which rule applies now ^[17]. TB-500 was also named on the July 23–24, 2026 PCAC agenda as a candidate being considered for the 503A bulks list; FDA staff had argued against listing it, and no outcome has been published ^[18].