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

The current FDA position on TB-500

TB-500 legal status starts from a fixed, 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 substances that may present significant safety risks — effective with FDA's September 29, 2023 update to the list of bulk drug substances nominated for use under section 503A ^[16][17]. FDA cited concerns including potential immunogenicity for certain routes of administration and a lack of important safety information ^[17]. 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 FDA's enforcement-discretion policy for 503A compounding ^[16][17]. And it is not an FDA-approved drug — it has no approved therapeutic indication ^[17]. 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 ^[16].

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.

Access is under active FDA review and may expand in 2026

The forward-looking fact is genuine, and it is stated with care. TB-500 — listed by FDA as "TB-500 (free base)" and "TB-500 acetate" — appears 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].

That is the whole of what can be asserted: a scheduled evaluation and discussion. It is not a listing decision, not a reclassification, and not a change in current status ^[18]. 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 ^[16]. The outcome of the July 2026 meeting is unknown and is not assumed here ^[18].

A note on what this page does not claim. Some commercial and clinic sources have reported an early-2026 reclassification of Category 2 peptides, and some assert specific 2026 dates on which substances were "removed" from Category 2. Those reports could not be confirmed from an authoritative FDA source, so this page does not present any reclassification or removal as having occurred ^[16]. The current category for TB-500 is stated as Category 2 — the last FDA action confirmable from FDA.gov — and the fact that PCAC still lists TB-500 for July 2026 is consistent with its evaluation being ongoing rather than resolved ^[18].

How legally compounded peptide access 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 compound larger batches under cGMP-style oversight ^[16].

In practice, a legally compounded medication is prepared only after an individual patient is evaluated by a licensed prescriber who determines a compounded preparation is appropriate and issues a valid, patient-specific prescription ^[16]. The preparation is then made by a state-licensed 503A compounding pharmacy or, for larger volumes, an FDA-registered 503B outsourcing facility ^[16]. Telehealth can serve as the front-end channel through which a patient is evaluated and a 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 ^[16].

The ingredient-eligibility caveat is the operative one for TB-500. 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 is on the relevant FDA bulks list ^[16]. A substance FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands — so a Category 2 substance such as TB-500 is not eligible under that framework as the status presently stands ^[16][17]. This is described in general terms; this page names no pharmacy, clinic, telehealth provider or vendor, gives no dosing, and describes no way to obtain a restricted substance outside the lawful framework.

Is TB-500 Legal?

TB-500 has no FDA-approved human therapeutic indication and is not an FDA-approved drug; FDA placed the LKKTETQ fragment in 503A Category 2 as a bulk substance that may present significant safety risks, effective September 29, 2023 ^[16][17]. It is sold by suppliers for laboratory and research use, is prohibited by WADA in sport, and is classified as a prescription medicine in some jurisdictions ^[15]. This is general regulatory information, not legal advice.

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 nominated-substances update, citing potential immunogenicity for certain routes and a lack of important safety information ^[16][17]. Category 2 substances are not within FDA's enforcement-discretion policy for 503A compounding ^[16]. TB-500 is separately listed for discussion at the July 23-24, 2026 PCAC meeting as a candidate for the 503A bulks list — a scheduled evaluation only, not a decision ^[18].

Can You Get TB-500 from a Compounding Pharmacy?

Lawful compounded access requires that the active ingredient be eligible under the 503A/503B framework — via a USP/NF monograph, status as a component of an approved drug, or inclusion on the FDA bulks list ^[16]. TB-500 is in 503A Category 2, which FDA does not afford enforcement discretion, so it is not eligible for routine 503A compounding while that status stands ^[16][17]. Any legitimate compounded preparation still requires a licensed-prescriber evaluation and a valid, patient-specific prescription ^[16]. This is general information, not advice, and not an offer to supply anything.

Is TB-500 FDA Approved?

No. TB-500 is not approved by the FDA for human use and has no approved therapeutic indication ^[17]. FDA reviewed peptide bulk drug substances, including the thymosin beta-4 LKKTETQ fragment, for compounding and flagged safety concerns, placing TB-500 in 503A Category 2 ^[16][17]. FDA approval of a finished drug is a separate question from compounding eligibility, and TB-500 meets neither — it is a research and veterinary-context substance, not an approved medicine ^[16][17].

Is TB-500 Legal to Use in Research?

TB-500 is sold by suppliers for laboratory and research use and has no approved human therapeutic indication ^[17]. It is prohibited by WADA in sport and is classified as a prescription medicine in some jurisdictions, such as Australia and New Zealand ^[15]. It is not intended or approved for human use; this site describes findings as studied at named doses in named species rather than recommending any human use ^[17].