# 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 is WADA-prohibited. How compounded peptide access works, and what the July 2026 PCAC agenda means.

Where TB-500 stands today under FDA's 503A compounding framework, the active review that may move it in 2026, and how legally compounded peptide access actually works. General information, not legal advice.

## TB-500 legal status and FDA 503A category, stated present-tense

TB-500 legal status, as a current and FDA-citable fact, is this: FDA — which lists the entry as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" — placed it in 503A "Category 2," the designation for bulk drug substances that may present significant safety risks, effective with FDA's September 29, 2023 nominated-substances update, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information [16]. As a Category 2 substance, TB-500 is not within FDA's enforcement-discretion policy for 503A compounding, and it is not an FDA-approved drug [16].

The framework behind that label matters. Under the Federal Food, Drug, and Cosmetic Act, Section 503A governs traditional patient-specific compounding by state-licensed pharmacies and physicians, and Section 503B governs FDA-registered outsourcing facilities that compound in larger volumes [17]. 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 FDA's 503A bulks list; substances not yet listed are evaluated through a public nomination process with input from the Pharmacy Compounding Advisory Committee (PCAC) [17]. FDA approval of a finished drug is a separate question from whether a bulk substance may be used in compounding — and TB-500 is neither approved nor within the enforcement-discretion policy as things stand [16][17].

### Is TB-500 FDA approved?

No. TB-500 — FDA's "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" — is not an FDA-approved drug, and it sits in 503A Category 2 (bulk substances that may present significant safety risks), outside FDA's enforcement-discretion policy for compounding [16]. It is a research and veterinary-context substance, not an approved medicine.

## Access is under active FDA review and may expand in 2026

There is real momentum to report, and it should be read as momentum, not as a decision. 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]. After years in Category 2, the fragment is on a scheduled evaluation docket — which is a meaningful sign that its status is being actively reconsidered.

The limits on that statement are firm, and this site holds them. A PCAC meeting is a scheduled evaluation and discussion only. It is not a listing decision, not a reclassification, and not a change in current status [18]. A PCAC discussion is advisory; the outcome is unknown and must not be assumed, stated, or dated. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by PCAC — being on the agenda is a step in evaluation, not the end of one [17][18].

Two widely circulated 2026 claims do not meet that bar and are excluded here. Reports that roughly 14 of the ~19 peptides placed in Category 2 in 2023 were expected to move back toward Category 1 could not be confirmed as a completed, effective FDA action from an authoritative FDA source; the most candid of those sources itself states the formal reclassification is still pending [19]. Separately, vendor and clinic pages asserting specific 2026 dates on which substances were "removed" from Category 2 could not be verified from an authoritative FDA source — and the standing PCAC agenda, which still lists TB-500 as under consideration for July 2026, is consistent with the evaluation being ongoing rather than resolved [19]. The honest present-tense position is Category 2, under active review, outcome unknown.

## How legally compounded peptide access works

In general terms, a legally compounded medication in the U.S. is prepared only after an individual patient is evaluated by an appropriately licensed prescriber who determines that a compounded preparation is clinically appropriate and issues a valid, patient-specific prescription [20]. The preparation is then made by a state-licensed 503A compounding pharmacy (patient-specific) or, for larger office or batch use, sourced from an FDA-registered 503B outsourcing facility [20]. Telehealth can serve as the front-end channel for the prescriber-evaluation step — a route to a licensed-prescriber consultation and prescription — 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 [20].

The ingredient-eligibility caveat is the part that governs TB-500 specifically. A compounder may use a requested active ingredient only if that ingredient is eligible under the 503A/503B bulk-substance rules — a USP/NF monograph, a component of an approved drug, or a place on the applicable FDA bulks list [20]. Ingredients FDA has flagged for significant safety risks are not eligible for routine 503A compounding while that status stands [20]. TB-500 is a Category 2 substance, so that caveat applies to it directly for as long as the current status holds [16].

This page is general information about the regulatory landscape. It is not medical or legal advice, it names no specific pharmacy, clinic, telehealth provider, or vendor, it provides no dosing or administration instructions, and it is not an offer to sell or supply any substance.

### Is TB-500 legal?

There is no single yes-or-no answer, because "legal" depends on the context. As an FDA matter, TB-500 is not an approved drug and sits in 503A Category 2 — outside FDA's enforcement-discretion policy for compounding while that status stands [16]. In sport, it is WADA-prohibited [5]. Some jurisdictions classify it as a prescription medicine. This site describes the U.S. regulatory landscape as general information, not legal advice.

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

Compounded access generally requires a licensed-prescriber evaluation, a valid patient-specific prescription, and an eligible active ingredient at a 503A pharmacy or 503B outsourcing facility [20]. A Category 2 substance is not eligible for routine 503A compounding while that status stands — which applies to TB-500 today [16]. The July 2026 PCAC meeting is a scheduled discussion of whether to consider it for the 503A bulks list, not a change in that status [18].

### 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 update, citing potential immunogenicity for certain routes and a lack of important safety information [16]. It is therefore not within FDA's enforcement-discretion policy for 503A compounding. "TB-500 (free base)" and "TB-500 acetate" are on the July 23–24, 2026 PCAC agenda for consideration, which is a scheduled evaluation, not a decision [18].

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

Yes. TB-500 falls under WADA's prohibited peptide/growth-factor and tissue-repair categories and is detected by LC-MS anti-doping assays [5]. It is banned in and out of competition for the relevant classes. It has been encountered as a designer tissue-repair drug in racehorses, which prompted equine and human anti-doping detection methods.

### Why is TB-500 used in racehorses?

TB-500 was encountered as a designer tissue-repair drug in racehorses, prompting equine LC-MS detection methods [5]. It is used in a veterinary and doping context, not as an approved equine medicine. The racehorse association is one reason the fragment is described together with anti-doping detection science rather than with an approved-drug record.

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A luminous console reading of the thymosin beta-4 literature — the Ac-LKKTETQ fragment mapped apart from the full-length protein it is sold as, the empty human-trial node and the FDA 503A status left lit, and no clinic behind the readout nor anything here dispensed.