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

> TB-500 legal status, cited to FDA: FDA placed Thymosin beta-4, fragment (LKKTETQ), also known as TB-500 in 503A Category 2, it is not FDA-approved, it is WADA-prohibited, and it is on a scheduled 2026 compounding-review agenda.

The present-tense regulatory record, read from FDA: a 503A Category 2 substance, not FDA-approved, WADA-prohibited — and individually named on a scheduled 2026 compounding-review agenda. General information, not legal or medical advice.

## The current FDA fact: TB-500 is a 503A Category 2 substance

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, as a Category 2 substance, TB-500 is **not** within FDA's enforcement-discretion policy for 503A compounding — the policy that lets compounders work with a substance while FDA continues its evaluation applies to Category 1, not Category 2 [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 is under active FDA review and may expand in 2026

The forward-looking fact is concrete and hedged. TB-500 — listed as "TB-500 (free base)" and "TB-500 acetate" — is individually named on the published agenda of the FDA Pharmacy Compounding Advisory Committee (PCAC) meeting scheduled for July 23–24, 2026, as a bulk drug substance "being considered for inclusion on the 503A Bulks List" [18]. The same agenda also lists BPC-157, KPV, and MOTs-C [18]. That a substance is named for discussion means its 503A eligibility is being actively evaluated.

This is momentum, not a decision. A scheduled PCAC meeting is an evaluation and discussion step, 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 the committee; being on the agenda is a step in that process, and the outcome is unknown [18]. Nothing here should be read as TB-500 having moved out of Category 2 or onto the bulks list. 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: Category 2 now, under active review, with a discussion scheduled for July 2026 and no outcome 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]. TB-500 fails both tests today: no approved finished drug, and a Category 2 standing that keeps it outside routine 503A compounding while that status holds [17]. The scheduled 2026 PCAC discussion concerns the compounding-eligibility question only, and does not change 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 a substance FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [17][19]. This is the [FDA 503A compounding access](/legal-status) reality for a Category 2 substance — 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 is not an FDA-approved drug and is not within FDA's enforcement-discretion policy for 503A compounding; FDA placed it in Category 2 (significant-safety-risk) effective with its September 29, 2023 update [17]. It is sold by suppliers for laboratory research use, it is WADA-prohibited in sport [10], and it is on a scheduled July 2026 FDA compounding-review agenda — a discussion, not a decision [18]. This is general information, not legal advice.

## Can you get TB-500 from a compounding pharmacy?

Not through routine 503A compounding while its current status stands. A 503A compounder may use a bulk substance only if it is eligible under the bulk-substance rules, and a Category 2 substance FDA has flagged for significant safety risks is not eligible for that routine compounding [17][19]. The lawful framework runs through a licensed-prescriber evaluation and a patient-specific prescription, but the ingredient-eligibility rule is the binding constraint here [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 [17]. TB-500 is also named on the July 23–24, 2026 PCAC agenda as a candidate being considered for the 503A bulks list — a scheduled discussion, not a decision [18].

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The TB-500 record sorted onto one flat status board — each study dropped into its evidence row, the Ac-LKKTETQ fragment kept apart from its parent protein thymosin beta-4, and the empty human-trial row left in plain sight; no clinic stands behind the board and nothing here is dispensed or sold.