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

> TB-500 legal status: FDA lists the LKKTETQ fragment as TB-500 and placed it in 503A Category 2 for significant safety risks. Access is under active FDA review and may expand in 2026. General information.

Where the fragment stands today with the FDA and WADA, why access is under active review, and how legally compounded peptide access actually works. General information, not medical or legal advice.

## The current FDA status, stated plainly

Here is the **TB-500 legal status** as it stands. The 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 the FDA's September 29, 2023 update to the list of substances nominated for use under section 503A [1]. The FDA cited concerns including potential immunogenicity for certain routes of administration and a lack of important safety information [1]. The FDA's own list entry establishes the relationship the rest of this site turns on: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 [1].

Two consequences follow directly. As a Category 2 substance, TB-500 is not within the FDA's enforcement-discretion policy for 503A compounding — the policy that, for Category 1 substances, signals the FDA does not intend to act against a compounder while evaluation continues does not cover it [2]. And TB-500 is not an FDA-approved drug; FDA approval of a finished drug is a separate question from whether a bulk substance may be used in compounding, and the fragment satisfies neither [2]. State both facts together and you have the present-tense reality: not approved, and not eligible for routine 503A compounding while this status stands.

## Why the door is not closed: access is under active review

The forward-leaning part is real, and it is anchored on a published fact. "TB-500 (free base)" and "TB-500 acetate" appear individually on the published agenda of the FDA Pharmacy Compounding Advisory Committee (PCAC) meeting scheduled for July 23–24, 2026, listed as bulk drug substances "being considered for inclusion on the 503A Bulks List" [3]. The same agenda lists BPC-157, KPV, and MOTs-C. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by the PCAC, and being discussed by the committee is a step in evaluation [2].

That is the honest shape of the momentum: TB-500's compounding eligibility is under active FDA review, and access may expand in 2026. But a scheduled PCAC discussion is advisory, not a decision. It is not a listing, not a reclassification, and not a change in current status [3]. No outcome should be assumed, stated, or dated. As of the last confirmable FDA action, the category is still Category 2 — and the fact that the fragment remains on a July 2026 agenda as a candidate is itself consistent with its evaluation being ongoing rather than resolved [reg-unc]. You may also see commercial or clinic sources claiming that peptides were "moved back" toward Category 1 in early 2026, or that TB-500 was "removed" from Category 2 on a specific 2026 date; those reports could not be confirmed from an authoritative FDA source and the most candid of them concede the formal reclassification is still pending, so this page does not treat any reclassification as having occurred [reg-unc].

## How legally compounded peptide access works

In the United States, 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 [2]. The preparation is then made either by a state-licensed 503A compounding pharmacy (patient-specific) or, for larger volumes, by an FDA-registered 503B outsourcing facility operating under cGMP-style oversight [2].

The pathway runs in one direction: licensed-prescriber evaluation → valid prescription → 503A compounding pharmacy or 503B outsourcing facility [2]. Telehealth can serve as the front-end channel through which a patient is evaluated and a prescription is issued, but it is a route to a licensed-prescriber consultation, not a separate legal status — it does not expand which substances may be compounded and does not remove the need for a legitimate clinical evaluation and a valid prescription [2]. The ingredient-eligibility caveat is the binding one for TB-500: a compounder may use a requested active ingredient only if that ingredient is eligible under the 503A/503B bulk-substance rules, and a substance the FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [2]. That is general information about the regulatory landscape — not medical or legal advice, not a protocol, and not an offer to supply any substance.

## Is TB-500 FDA approved?

No. **Is TB-500 FDA approved** has a clean answer: the FDA has not approved TB-500 for any human use, and it has no approved therapeutic indication [1]. It is a research-chemical and veterinary-context substance, not an approved medicine. FDA approval of a finished drug is a distinct legal question from whether a bulk substance may be used in compounding, and TB-500 meets neither bar — it is not approved, and as a 503A Category 2 substance it is not within the FDA's enforcement-discretion policy for compounding [1][2].

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

TB-500 is in 503A Category 2: a bulk drug substance the FDA identified as one that may present significant safety risks, placed there effective with the September 29, 2023 nominated-substances update, citing concerns including potential immunogenicity for certain routes and a lack of important safety information [1]. Category 2 substances are not covered by the enforcement-discretion policy that applies to Category 1, and the FDA has said it would consider acting against a compounder for compounding with one [2]. The fragment is also on the July 23–24, 2026 PCAC agenda as a candidate for the bulks list — a scheduled discussion under evaluation, not a decision [3].

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

Under the framework as it stands, no — not through routine 503A compounding. A 503A compounding pharmacy may use a bulk substance only if it has an applicable USP/NF monograph, is a component of an FDA-approved drug, or appears on the FDA's 503A bulks list; TB-500 satisfies none of these, and as a Category 2 substance it is not eligible for routine 503A compounding while that status stands [2][1]. Any lawful access would still require a licensed-prescriber evaluation and a valid prescription, and the ingredient-eligibility rule is the gate the fragment does not currently clear [2]. This is general regulatory information, not advice on how to obtain the substance.

## 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 and growth-factor / tissue-repair categories and are banned in and out of competition for the relevant classes [5]. The substance is detected by LC-MS anti-doping assays in equine and human matrices [5]. WADA prohibition is independent of the FDA compounding question — a substance can be banned in sport regardless of its compounding status — and both stand against TB-500 today.

## Why is TB-500 used in racehorses?

TB-500 was marketed as a veterinary preparation and was encountered as a designer drug in racehorses, which prompted the first equine LC-MS detection methods to control its misuse in sport [5]. That veterinary and anti-doping history is part of why the fragment is named the way it is — "TB-500" is a research and veterinary designation — and why analytical detection of the seven-mer, rather than human pharmacology, is where much of the non-academic literature on it actually sits.

## Is TB-500 legal?

There is no single yes-or-no answer; legality depends entirely on context. As a matter of FDA status, TB-500 is not an approved drug and is in 503A Category 2, not eligible for routine 503A compounding while that status stands [1][2]. In sport, it is prohibited by WADA [5]. It is sold by research suppliers for laboratory use and has been classified as a prescription medicine in some jurisdictions [5]. This page is general information about that regulatory landscape — not medical or legal advice, and not an offer to sell or supply any substance.

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A constructivist broadsheet of the TB-500 record — the Ac-LKKTETQ fragment typeset against the thymosin beta-4 protein where the data live, the angiogenesis lens set beside its tumor signal, and the FDA 503A and WADA standing composed before anything else; no clinic behind the masthead and nothing here dispensed or sold.