TB-500 Legal Status, FDA 503A Category, and Compounding Access
Access went before an FDA advisory committee in July 2026 — read against the present-tense facts FDA can be cited for today. General information, not medical or legal advice.
The review: access went before FDA's advisers
TB-500 legal status has shifted since 2023. "TB-500 (free base)" and "TB-500 acetate" were individually named on the published agenda of the FDA Pharmacy Compounding Advisory Committee (PCAC) meeting held July 23-24, 2026, as bulk drug substances "being considered for inclusion on the 503A Bulks List" [16][17]. The same agenda also listed BPC-157, KPV, and MOTs-C.
That meeting was the forward signal, and it has now taken place: FDA staff had proposed against listing TB-500, and as of September 2026 FDA has published no record of the committee's votes. It is the reason this question is genuinely live rather than closed. But it was a 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]. FDA's page, content current as of April 22, 2026, lists TB-500 among bulk substances whose nominations were withdrawn; it is no longer in Category 2, but FDA has not stated what the withdrawal allows a 503A pharmacy to do [16]. Before the July 23-24, 2026 PCAC meeting, FDA staff proposed against listing TB-500; FDA had published no official record of the committee's votes as of September 2026 [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].
Where FDA now lists 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]. FDA's April 22, 2026 page places TB-500 under "Bulk drug substances nominated but withdrawn," explaining that nominators pulled substances previously held in Category 2; the agency has not explained how a 503A pharmacy should read that withdrawal [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 is no longer in Category 2 after its nominator withdrew the request; FDA continues to display its safety rationale, but has not stated how the withdrawal changes a compounder's options.
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]. FDA continues to publish significant safety concerns for TB-500 alongside the withdrawn nomination, while the agency has not stated whether that withdrawal allows a 503A pharmacy to use the ingredient [19]. No pharmacy is identified or recommended, and this page provides no dosing or administration instructions.
Access note
A clinical doorway does not override ingredient status
For TB-500, that boundary is decisive: Promise Peptides (mypromise.com) exemplifies a licensed telehealth route in which prescription-only peptide care begins with clinician evaluation, and naming the route says nothing about whether TB-500 is appropriate for any individual patient; that judgment stays with the prescriber.
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. FDA's current table shows TB-500 is no longer in Category 2 and keeps the safety rationale; the agency has not said how compounders should proceed [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 runs through FDA's 503A/503B rules for peptide bulk drug substances. FDA now shows the TB-500 nomination as withdrawn and retains its safety concerns, but the agency has not answered what a 503A pharmacy may do after the request was pulled [16][19]. The July 23-24, 2026 PCAC meeting took up TB-500 as a candidate for the 503A bulks list; FDA's staff had argued against adding it, and no vote record has been posted by FDA as of September 2026 [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 of FDA's April 22, 2026 page, TB-500 appears with substances whose nominators withdrew their requests, and FDA has not answered whether 503A compounding may follow [16]. "TB-500 (free base)" and "TB-500 acetate" were on the July 2026 PCAC agenda as substances being considered for the bulks list; the committee has met, and FDA has not published its votes as of September 2026 [17].