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

> TB-500 legal status: FDA placed the thymosin beta-4 LKKTETQ fragment (TB-500) in 503A Category 2, access is under active FDA review and may expand in 2026, and how compounded peptide access lawfully works.

Access is under active FDA review and may widen in 2026 — read against the present-tense facts FDA can be cited for today. General information, not medical or legal advice.

## 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].

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A case review of the TB-500 evidence — every finding tagged for the molecule it is on, no clinic behind the file and nothing here for sale.