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

> TB-500 legal status: FDA placed the thymosin beta-4 LKKTETQ fragment in 503A Category 2, it is not FDA-approved, and access is under active FDA review for a July 2026 PCAC meeting.

Access is under active FDA review and may expand in 2026 — but the present-tense facts are precise, and this page states them as facts, not predictions.

## The current FDA fact

TB-500 legal status begins with one citable fact. FDA lists the substance 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 — effective with FDA's September 29, 2023 update to the list of substances nominated for use under section 503A [16]. FDA's stated rationale includes concerns such as potential immunogenicity for certain routes of administration and a lack of important safety information [16]. FDA's own list entry establishes the relationship between the two names: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 [16].

Two consequences follow directly. As a Category 2 substance, TB-500 is not within FDA's enforcement-discretion policy for 503A compounding — the policy that applies to Category 1 substances does not apply here [17]. And TB-500 is not an FDA-approved drug for any indication [16]. Those are the present-tense facts, and the rest of this page is anchored to them.

## What is changing — and what is not

Here is the forward-leaning part, stated carefully. "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, as bulk drug substances "being considered for inclusion on the 503A Bulks List" — the same agenda that also lists BPC-157, KPV, and MOTs-C [18]. Access to this class is under active FDA review, and it may expand in 2026. That is real momentum, and it is the honest top-line for anyone tracking this.

Now the equally important limit. A PCAC meeting is a scheduled evaluation and discussion only. It is not a listing decision, not a reclassification, and not a change in TB-500's current status [18]. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by the committee — being discussed by PCAC is a step in evaluation, not an outcome [17]. The fact that TB-500 is still listed as "being considered" for July 2026 is itself consistent with its evaluation being ongoing rather than resolved. This page does not state, date, or assume any outcome, and it does not repeat unconfirmed reports of a 2026 reclassification or removal that could not be verified against an authoritative FDA source.

## How the 503A and 503B framework works

Under the U.S. 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. Section 503B covers FDA-registered "outsourcing facilities" that may compound larger batches under cGMP-style oversight and FDA inspection [17].

The ingredient rule is what makes TB-500's category matter. 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 [17]. Substances not yet on a bulks list are evaluated by FDA through a public nomination process with input from PCAC. Because FDA placed TB-500 in Category 2, it is not eligible for routine 503A compounding while that status stands [17]. Separately, FDA approval of a finished drug is a different question from whether a bulk substance may be used in compounding — and TB-500 is neither approved nor on a final bulks list today [16].

## How legally compounded peptide access works, in general terms

Described generally — not as medical or legal advice, and not as an offer to supply anything — a legally compounded medication in the U.S. 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 [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].

Telehealth can serve as the front-end channel through which the patient is evaluated and the prescription 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 [17]. The ingredient-eligibility caveat governs the whole pathway: a compounder may use a requested active ingredient only if that ingredient is eligible under the 503A/503B bulk-substance rules, and an ingredient FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [17]. This page names no pharmacy, clinic, telehealth provider, or vendor, gives no dosing, and describes no way to obtain a restricted substance outside that lawful framework.

## TB-500 and anti-doping status

Separate from the FDA compounding question, TB-500 is prohibited in sport. TB-500 and thymosin beta-4 fall under the World Anti-Doping Agency's prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition for the relevant classes, and are detected by LC-MS anti-doping assays in equine and human matrices [4][16]. Athletes subject to anti-doping codes should treat the substance as prohibited regardless of how the compounding question evolves.

## Is TB-500 FDA approved?

No. TB-500 has no FDA-approved therapeutic indication [16]. It is a research and veterinary-context substance, and the human data that exist are for full-length thymosin beta-4, not the fragment [4]. FDA approval of a finished drug is a separate question from whether the bulk substance may be used in compounding, and TB-500 satisfies neither today [16][17].

## Is TB-500 legal?

The precise statement is regulatory, not a simple yes or no. TB-500 has no FDA-approved human indication, is sold by research suppliers for laboratory use only, is prohibited in sport by WADA, and is classified as a prescription medicine in some jurisdictions such as Australia and New Zealand [16][4]. FDA placed it in 503A Category 2, so it is not eligible for routine 503A compounding while that status stands [16][17]. This is general information about the regulatory landscape, not legal advice.

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

Because FDA placed TB-500 in 503A Category 2 as a substance that may present significant safety risks, it is not eligible for routine 503A compounding while that status stands [16][17]. The general compounding pathway requires a licensed-prescriber evaluation, a valid patient-specific prescription, and an eligible ingredient [17]. This page describes that framework in general terms and names no pharmacy or vendor.

## 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, effective with the September 29, 2023 nominated-substances update, citing concerns including potential immunogenicity for certain routes and a lack of important safety information [16]. Category 2 substances are not within FDA's enforcement-discretion policy [17]. TB-500 is also on the July 23–24, 2026 PCAC agenda as a substance being considered for the 503A bulks list — a scheduled discussion, not a decision [18].

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

Yes. TB-500 and thymosin beta-4 fall under WADA's prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition for the relevant classes, and they are detected by LC-MS anti-doping assays [4][16]. The prohibition is independent of the FDA compounding question and applies to athletes under anti-doping codes regardless of jurisdiction.

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A clear-eyed digest of the TB-500 and thymosin beta-4 record, read by glow intensity — the established findings bright, the human-data gaps left dim and labeled, with no clinic behind the aurora and nothing here dispensed.