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

> TB-500 legal status: FDA placed 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' in 503A Category 2 (significant safety risks). Not FDA-approved. Under active review — named on the July 2026 PCAC agenda.

The current FDA standing, stated present-tense and cited — plus the scheduled 2026 review that may move it, framed as a discussion and not a decision.

## TB-500 legal status: under active FDA review, with a real chance of change in 2026

TB-500 legal status is, right now, an open file that the FDA has scheduled to reopen. The single most consequential fact for anyone reading this: TB-500 — listed by the FDA as "TB-500 (free base)" and "TB-500 acetate" — is named individually 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]. Access to legally compounded TB-500 is under active review and may expand in 2026.

That is the forward-leaning part, and it is bounded carefully. A PCAC listing 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 a final listing [19]. No outcome of the July 2026 meeting should be assumed [18].

This page is general information about the regulatory landscape. It is not medical or legal advice, and it is not an offer to sell or supply any substance.

## The current fact: 503A Category 2, not FDA-approved

As of now, the FDA standing is specific and citable. The FDA identified "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" as a bulk drug substance that may present significant safety risks and placed it in 503A Category 2, effective with the FDA's September 29, 2023 update to the nominated-substances list, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information [20]. The FDA's own list entry establishes the relationship: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 [20].

Category 2 has a defined meaning. Under the FDA's interim policy, Category 2 bulk drug substances are those nominated with sufficient information for the FDA to evaluate but which the FDA has identified as raising significant safety risks; they are not covered by the enforcement-discretion policy that applies to Category 1, and the FDA stated it would consider taking action against a compounder for compounding with a Category 2 substance [19]. So as a Category 2 substance, TB-500 is not within the FDA's enforcement-discretion policy for 503A compounding, and it is not an FDA-approved drug [20].

Two separate questions sit behind that. FDA approval of a finished drug (a New Drug Application or Biologics License Application) is distinct from whether a bulk substance may be used in compounding; TB-500 is neither an approved drug nor, while Category 2 stands, eligible for routine 503A compounding [19][20].

## How legally compounded peptide access works

Compounded medication access follows a defined, prescriber-anchored pathway. A legally compounded preparation is made 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 [21]. 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 operating under cGMP-style oversight [21].

Telehealth fits at the front end, not as a separate legal status. It can serve as the channel through which a patient is evaluated and a prescription is 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 [21].

The ingredient-eligibility caveat is the operative limit here. A compounder may use a bulk drug substance only if it is the subject of an applicable USP/NF monograph, is a component of an FDA-approved drug, or appears on the relevant FDA bulks list [19]. A substance the FDA has flagged for significant safety risks — a Category 2 substance such as TB-500 — is not eligible for routine 503A compounding while that status stands [21]. None of this is dosing guidance, and none of it names or endorses any pharmacy, clinic, telehealth provider, or vendor.

## Regulatory FAQ

Direct answers to the regulatory questions, drawn only from the audited FDA reference. Present-tense facts; no future FDA action is stated as decided or dated.

#### Is TB-500 FDA approved?

No. TB-500 is not an FDA-approved drug and has no approved therapeutic indication. The FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 — bulk substances identified as raising significant safety risks — effective with its September 29, 2023 update, citing potential immunogenicity for certain routes and a lack of important safety information [20].

#### Is TB-500 legal?

There is no single yes/no answer, and this is general information, not legal advice. In the U.S. compounding context, the FDA placed TB-500 in 503A Category 2, so it is not within the FDA's enforcement-discretion policy for routine 503A compounding and is not an FDA-approved drug [19][20]. Separately, TB-500 is prohibited in sport by WADA [22]. Status varies by jurisdiction and context.

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

Legally compounded medications require a licensed-prescriber evaluation and a valid, patient-specific prescription, dispensed by a 503A pharmacy or 503B outsourcing facility [21]. A compounder may use an ingredient only if it is eligible under the 503A/503B bulk-substance rules; a Category 2 substance the FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [19][21].

#### 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 drug substances that may present significant safety risks — effective with its September 29, 2023 nominated-substances update [20]. Category 2 substances are not covered by the FDA's enforcement-discretion policy for 503A compounding [19]. TB-500 is also named on the July 23-24, 2026 PCAC agenda for evaluation, which is a scheduled discussion, not a decision [18].

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The TB-500 literature drawn to spec on a single drawing sheet — the Ac-LKKTETQ fragment dimensioned out from its thymosin beta-4 parent, the empty human-trial cell left in the title block, and the FDA 503A standing stamped before anything else; no clinic drafted it and nothing here is dispensed or sold.