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

Where TB-500 stands today, present-tense

Start with the current fact. TB-500 — which the FDA lists as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" — is a research peptide that the FDA placed in 503A "Category 2" (bulk substances that may present significant safety risks), effective with the FDA's September 29, 2023 update to its list of nominated substances, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information ^[17]. The FDA's own list entry establishes the relationship: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 ^[17].

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 applies to Category 1 substances does not cover it ^[18]. And TB-500 is not an FDA-approved drug; approval of a finished drug is a separate question from whether a bulk substance may be used in compounding, and TB-500 has no approved therapeutic indication ^[18]. This is the last FDA action confirmable from FDA.gov, and it is the status this page states as current ^[17].

Why access may expand in 2026 — and what is actually scheduled

The momentum is real, and it is specific. "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" ^[19]. The same agenda also lists BPC-157, KPV, and MOTs-C ^[19]. That places TB-500 squarely inside an active evaluation: the FDA is scheduled to discuss whether it should join the list of substances permitted in 503A compounding.

What that is, precisely: a scheduled evaluation and discussion. What it is not: a listing decision, a reclassification, or a change in current status. Inclusion on a final 503A bulks list is decided by FDA rulemaking informed by the PCAC; being discussed by the committee is a step in evaluation, not a final listing decision, and a PCAC discussion is advisory rather than determinative ^[18]. No outcome of the July 2026 meeting should be assumed or dated — the agenda confirms the question is open, not that it is answered ^[19]. Read honestly, the news is that TB-500 is being looked at again; the verdict has not been written.

For completeness: some commercial and clinic sources have reported an early-2026 expectation that a group of Category 2 peptides would move back toward Category 1, and specific dated "removal" claims for individual peptides. As of the audited review date those reports could not be confirmed from an authoritative FDA source, and the most candid of them acknowledged the formal reclassification was still pending — so this page does not treat any reclassification as having occurred ^[18]. The PCAC agenda still listing TB-500 for July 2026 is consistent with its evaluation being ongoing rather than resolved ^[19].

How legally compounded peptide access works

U.S. drug compounding runs through two sections of the Federal Food, Drug, and Cosmetic Act. Section 503A covers traditional, patient-specific compounding by state-licensed pharmacies and licensed physicians, generally pursuant to a valid prescription for an individual patient; Section 503B covers FDA-registered "outsourcing facilities" that compound larger batches under cGMP-style oversight and FDA registration and inspection ^[18]. 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 the relevant FDA bulks list; substances not yet on a list are evaluated by the FDA through a public nomination process with input from the PCAC ^[18].

In practice the pathway is sequential. A patient is evaluated by an appropriately licensed prescriber — in person or through a compliant telehealth encounter — who determines whether a compounded preparation is clinically appropriate ^[20]. If it is appropriate and lawful, the prescriber issues a valid, patient-specific prescription ^[20]. That prescription is then dispensed by a state-licensed 503A compounding pharmacy, or, for office and batch use, sourced from an FDA-registered 503B outsourcing facility ^[20]. Telehealth can serve as the front-end channel for the evaluation and prescription, but it does not change which substances are eligible to be compounded or remove the need for a legitimate prescriber-patient relationship and a valid prescription ^[20].

There is one ingredient-eligibility caveat that governs all of the above for this compound: a compounder may use a requested active ingredient only if that ingredient is eligible under the 503A/503B bulk-substance rules, and an ingredient the FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands ^[20]. TB-500's Category 2 placement is exactly such a flag, which is why its current status and its presence on the July 2026 PCAC agenda are the two facts that matter most for access ^[17][19]. This site does not name any pharmacy, clinic, telehealth provider, or vendor, does not provide dosing or administration instructions, and does not describe any way to obtain a substance outside the lawful framework.

TB-500 in sport: the WADA position

Separately from the compounding question, TB-500 is prohibited in sport. TB-500 and thymosin beta-4 fall under the World Anti-Doping Agency's prohibited peptide and 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 ^[16]. TB-500 has also been encountered as a designer substance in racehorses, which prompted the development of equine and human anti-doping detection methods ^[16]. The WADA prohibition is independent of the FDA compounding status and applies regardless of how a substance is obtained.

Questions on legal status and access

This is general information about the regulatory landscape, not medical or legal advice, and not an offer to sell or supply any substance. The three questions below are answered from the audited FDA reference.

Is TB-500 legal?

TB-500 is sold for laboratory research use only and is not an FDA-approved drug for human use; it is WADA-prohibited in sport and is classified as a prescription medicine in some jurisdictions ^[16]. In U.S. compounding it sits in 503A Category 2, outside the FDA's enforcement-discretion policy ^[17]. "Legal" depends entirely on context — research supply, sport, and compounding are three different frameworks, covered above ^[18].

Can you get TB-500 from a compounding pharmacy?

Not through routine 503A compounding while its current status stands: the FDA placed the LKKTETQ fragment marketed as TB-500 in Category 2, identifying it as a bulk substance that may present significant safety risks, which means it is not eligible for routine 503A compounding ^[17]. A compounder may only use a bulk ingredient that is on the relevant FDA bulks list, has a USP/NF monograph, or is a component of an approved drug — TB-500 meets none of these today ^[18].

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

TB-500 is in 503A "Category 2" — bulk substances that may present significant safety risks — effective with the FDA's September 29, 2023 nominated-substances update, citing potential immunogenicity for certain routes and a lack of important safety information; it is not within the enforcement-discretion policy that covers Category 1 and is not an FDA-approved drug ^[17]. It is named on the July 23-24, 2026 PCAC agenda as being considered for the 503A Bulks List — a scheduled discussion, not a decision ^[19].