# TB-500 Legal Status, FDA 503A Category, and Compounding Access | TB-500 > TB-500 legal status: FDA lists the LKKTETQ thymosin beta-4 fragment as Category 2 for 503A compounding, and 'TB-500' is on the July 2026 PCAC agenda under active review. General information, not legal advice. The access record rendered as a status manifest: where the fragment sits today under FDA's 503A framework, and the one scheduled review worth watching — stated as a discussion, not a decision. ## TB-500 legal status and the FDA 503A category, stated plainly The TB-500 legal status begins with one present-tense fact. FDA lists this 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 nominated substances, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information [16]. FDA's own list entry establishes the relationship: 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 extend to it [17]. And it 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 TB-500 satisfies neither [17]. That is the floor on which everything else here stands. ## What 503A Category 2 means — and what it does not Under the Federal Food, Drug, and Cosmetic Act, compounding runs through two sections: 503A covers patient-specific compounding by state-licensed pharmacies and physicians under a valid prescription, and 503B covers FDA-registered outsourcing facilities compounding larger batches under cGMP-style oversight [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 on a list are evaluated through a public nomination process with input from the Pharmacy Compounding Advisory Committee (PCAC) [17]. FDA's interim policy sorted nominated substances into categories. Category 1 substances may be eligible for the bulks list and are covered by enforcement discretion while FDA evaluates them; Category 2 substances were identified as raising significant safety risks and are explicitly not afforded that discretion [17]. TB-500 sits in Category 2. What that does **not** mean: it is not a scheduling decision, not a ban on the molecule as such, and not a statement about any use outside the compounding framework — it is a statement that the ingredient is not eligible for routine 503A compounding while that status stands. ## Under active review: the July 2026 PCAC meeting The forward-looking part of the record is real, and it is worth stating with momentum — and with discipline. Access to compounded TB-500 is under active FDA review and may expand. "TB-500 (free base)" and "TB-500 acetate" appear individually on the published agenda of the FDA Pharmacy Compounding Advisory Committee meeting scheduled for July 23-24, 2026, as bulk drug substances "being considered for inclusion on the 503A Bulks List" — the same agenda that lists BPC-157, KPV and MOTs-C [18]. Here is the discipline. That is a scheduled evaluation and discussion **only**. It is not a listing decision, not a reclassification, and not a change in current status — a PCAC discussion is advisory, and inclusion on a final bulks list is decided by FDA rulemaking, not by being placed on a meeting agenda [17][18]. The current category for TB-500 remains Category 2 [16]. No outcome of the July 2026 meeting should be assumed, and no future FDA action carries a date here. The honest reading is: momentum, under review, status unchanged until FDA acts. ## How legally compounded peptide access works In general terms, and as background rather than instruction, a legally compounded medication in the U.S. is prepared only after a specific 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 office and batch use, sourced from an FDA-registered 503B outsourcing facility — registered outsourcing facilities compound larger batches under cGMP-style oversight and FDA inspection [17]. Telehealth can serve as the front-end channel through which that evaluation happens and a prescription is issued, but it does not change which substances are eligible to be compounded and does not remove the need for a legitimate prescriber-patient relationship and a valid prescription [17]. It is a route to a consultation, not a separate legal status. And the ingredient-eligibility caveat governs the whole pathway: a compounder may use a requested ingredient only if it is eligible under the 503A/503B bulk-substance rules — an applicable USP/NF monograph, a component of an FDA-approved drug, or a place on the applicable FDA bulks list — and an ingredient FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [17]. For TB-500, that is the current state: a Category 2 bulk substance, under evaluation, not on the bulks list. None of the above is medical or legal advice, names any pharmacy, clinic, telehealth provider or vendor, or describes a way to obtain any substance — it is general information about how the regulatory landscape is structured, and not an offer to sell or supply anything. --- A developer-console reading of the TB-500 record — the actin-binding fragment logged against its studies, with the full-length thymosin beta-4 caveat flagged in every diff, no clinic behind the terminal and nothing here prescribed or sold.