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

The momentum: access is under active FDA review

TB-500 legal status is moving. "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" ^[16][17]. The same agenda also lists BPC-157, KPV, and MOTs-C.

That is the forward signal: the path that could widen lawful compounded access runs through a scheduled FDA evaluation of TB-500, and it is happening in 2026. It is the reason this question is genuinely live rather than closed. But it is a scheduled discussion and nothing more — a PCAC evaluation is advisory, not a listing decision, not a reclassification, and not a change in current status. No outcome is assumed, stated, or dated here.

Is TB-500 FDA approved? The current fact

TB-500 is not an FDA-approved drug. FDA lists the substance as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500," and its own list entry establishes the relationship: TB-500 is the LKKTETQ fragment associated with thymosin beta-4 ^[16].

FDA placed that substance 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 substances nominated for use under section 503A ^[16]. FDA cited 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]. That is the present-tense status, and the July 2026 PCAC listing as a substance still "being considered" is consistent with its evaluation being ongoing rather than resolved ^[17].

How the 503A and 503B framework works

Under the Federal Food, Drug, and Cosmetic Act, drug compounding runs through two sections ^[18]. Section 503A covers traditional, patient-specific compounding by state-licensed pharmacies, federal facilities, and licensed physicians, generally pursuant to a valid prescription for an individual patient. Section 503B covers registered "outsourcing facilities" that may compound larger batches under cGMP-style oversight and FDA registration and inspection ^[18].

A compounder may use a bulk drug substance — an active ingredient used as a starting material, rather than an FDA-approved finished drug — only if that substance has an applicable USP/NF monograph, is a component of an FDA-approved drug, or appears on the relevant FDA bulks list ^[18]. Substances not yet on a bulks list are evaluated through a public nomination process with input from the PCAC. 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 an approved drug nor on the final 503A bulks list ^[16][18].

What Category 2 means for TB-500

Category 2 bulk drug substances are those nominated with enough information for FDA to evaluate, but that FDA identified as raising significant safety risks ^[18]. They are not covered by the enforcement-discretion policy that applies to Category 1, and FDA stated it would consider taking action against a compounder for compounding with a Category 2 substance ^[18].

A further procedural note: on January 7, 2025, FDA finalized a revised interim policy under which it no longer sorts newly nominated substances into these numbered categories; substances already in Category 1 may continue within the interim enforcement-discretion policy, while FDA has stated Category 2 substances are not afforded that discretion even if nominations are updated ^[18][20]. TB-500's status, as confirmable from FDA today, is Category 2.

How lawful compounded peptide access works

A legally compounded medication is prepared 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 ^[19]. The preparation is then made by a state-licensed 503A compounding pharmacy or, for larger volumes, by an FDA-registered 503B outsourcing facility ^[19].

Telehealth can serve as the front-end channel through which a patient is evaluated and a prescription is issued, 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 ^[19]. The decisive caveat for TB-500: a compounded preparation may lawfully be made only when its active ingredient is permitted under the 503A/503B framework, and an ingredient FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands ^[19]. This page names no specific pharmacy, clinic, telehealth provider, or vendor, and it provides no dosing or administration instructions.

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

Yes. TB-500 and thymosin beta-4 fall under WADA's prohibited peptide/growth-factor and tissue-repair categories, banned both in and out of competition for the relevant classes, and are detectable by LC-MS anti-doping assays in equine and human matrices. TB-500 has been encountered as a designer drug in racehorses, which prompted the development of equine and human anti-doping detection methods. It is also classified as a prescription medicine in some jurisdictions, such as Australia and New Zealand.

Is TB-500 legal?

TB-500 is not an approved medicine. It is sold by research suppliers for laboratory use, is classified as a prescription medicine in some jurisdictions, and is prohibited by WADA in sport. Under U.S. compounding rules it sits in 503A Category 2, outside FDA's enforcement-discretion policy ^[16]. "Legal" therefore depends on context — research use, sport, and the compounding question are separate. This is general information about the regulatory landscape, not legal advice.

Can you get TB-500 from a compounding pharmacy?

Access through compounding is constrained by FDA's review of peptide bulk drug substances under the 503A/503B framework. As a Category 2 substance, TB-500 is not eligible for routine 503A compounding while that status stands ^[16][19]. The July 23-24, 2026 PCAC meeting is scheduled to discuss TB-500 as a candidate for the 503A bulks list, but that is an evaluation, not a decision ^[17]. No specific pharmacy or provider is named here, and this is not an offer to supply any substance.

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]. As Category 2, it is outside FDA's enforcement-discretion policy for 503A compounding ^[16]. "TB-500 (free base)" and "TB-500 acetate" are on the July 2026 PCAC agenda as substances still being considered for the bulks list — a scheduled discussion, not a listing decision ^[17].