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

> TB-500 legal status: the FDA lists the LKKTETQ thymosin beta-4 fragment as a Category 2 bulk substance for 503A compounding and it is not an FDA-approved drug. Access is under active FDA review and may expand in 2026. General regulatory information, not legal advice. Cited to FDA.

Where the regulatory trace stands today — and the single board-level fact pointing forward: TB-500 is named on a scheduled 2026 FDA advisory-committee agenda.

## Where TB-500 legal status stands now

TB-500 legal status is, before anything else, a compounding-eligibility question — and the present fact is specific. The FDA lists the entry as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" and placed it in 503A "Category 2": bulk drug substances that may present significant safety risks [16]. That placement took effect with the FDA's September 29, 2023 update to the list of nominated substances, and the FDA's stated rationale included potential immunogenicity for certain routes of administration and a lack of important safety information [16]. The FDA's own list entry establishes the relationship the rest of this site keeps flagged: TB-500 is the LKKTETQ fragment associated with thymosin beta-4.

Two consequences follow directly. As a Category 2 substance, TB-500 is **not** within the FDA's enforcement-discretion policy for 503A compounding [16][17]. And TB-500 is **not** an FDA-approved drug — no New Drug Application or Biologics License Application has approved it for any human indication [17]. FDA approval of a finished drug and eligibility of a bulk substance for compounding are two separate questions, and TB-500 clears neither today.

## What is moving — and what is not

There is real, current momentum to read here, and it is worth leading with: access is under active FDA review and may expand in 2026. That statement rests on one verifiable, FDA-published fact. "TB-500 (free base)" and "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" [18]. The same agenda also lists BPC-157, KPV, and MOTs-C [18]. Being placed on the agenda means the substance is under evaluation — a step that could, over time, change its standing.

What that agenda is **not** must be stated as plainly. A scheduled PCAC discussion is advisory and evaluative only. It is not a listing decision, not a reclassification, and not a change in TB-500's current status [18][17]. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by the committee, and being discussed by the committee is a step in evaluation, not the outcome of it [17]. No result of the July 2026 meeting should be assumed, dated, or treated as already decided. As of this writing, the last FDA action confirmable from FDA.gov is the Category 2 placement [16] — that is the present-tense fact, and the agenda is a forward signal layered on top of it, not a replacement for it.

## Is TB-500 FDA approved?

No. TB-500 has no FDA-approved therapeutic indication; it is not an FDA-approved drug [16][17]. The FDA has evaluated the LKKTETQ thymosin beta-4 fragment as a bulk drug substance for compounding and placed it in Category 2, citing significant safety concerns [16]. Approval of a finished medicine is a separate process from the compounding-eligibility review, and TB-500 has not been through it for any human use.

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

The 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 update to the nominated-substances list [16]. Category 2 substances are not covered by the FDA's enforcement-discretion policy for 503A compounding [16][17]. Separately, TB-500 is named on the FDA's published agenda for 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 legal?

TB-500 is not an FDA-approved drug and, as an FDA Category 2 bulk substance, is not within the enforcement-discretion policy for routine 503A compounding [16][17]. It is supplied for laboratory research and is encountered in a veterinary context, and it is prohibited in sport by the World Anti-Doping Agency [15]. "Legal" depends on jurisdiction and use; what can be stated from authoritative U.S. sources is the FDA standing above. This page is general regulatory information, not legal advice.

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

How legally compounded peptide access works is worth understanding in general terms, because the ingredient-eligibility rule is the gate. In the U.S., a compounded medication is prepared only after a licensed prescriber evaluates an individual patient — in person or through a compliant telehealth encounter, which can serve as the front-end channel — and issues a valid, patient-specific prescription [17]. 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 [17].

The ingredient caveat is decisive. A compounder may use a bulk substance only if it is eligible under the 503A/503B rules — covered by a USP/NF monograph, a component of an approved drug, or on the applicable FDA bulks list — and a substance the FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [17]. Because TB-500 is currently a Category 2 substance [16], that eligibility gate is the operative constraint today. Telehealth is one channel to the prescriber-evaluation step; it does not expand which substances may be compounded and does not remove the need for a legitimate clinical evaluation and a valid prescription [17]. This is general information about the regulatory landscape — not medical or legal advice, and not an offer to sell or supply any substance.

## Why is TB-500 associated with racehorses?

TB-500 (Ac-LKKTETQ) has been supplied as a veterinary preparation and encountered as a designer drug in racehorses, which prompted LC-MS anti-doping detection methods in equine plasma and urine [15]. It is a controlled and prohibited substance in horse sport, and the same anti-doping science underlies its detection in human matrices. The equine context is part of why the compound exists in commerce under the TB-500 name rather than as an approved human medicine.

## Is TB-500 banned by WADA?

Yes. TB-500 and thymosin β4 fall under the World Anti-Doping Agency's prohibited peptide, growth-factor, and tissue-repair categories — banned both in and out of competition for the relevant classes — and are detected by LC-MS anti-doping assays in equine and human matrices [15]. For any athlete subject to anti-doping rules, TB-500 is prohibited regardless of its compounding-eligibility standing under the FDA framework.

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A cool-green research board for the TB-500 record — the Ac-LKKTETQ fragment routed as its own net apart from the full-length thymosin beta-4 it is sold as, the empty human-trial pad left open, the tumor-angiogenesis trace flagged and the FDA 503A standing read first; no clinic solders this board and nothing here is dispensed or sold.