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

> TB-500 legal status: FDA placed 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' in 503A Category 2; it is not FDA-approved. Access is under active FDA review for 2026. Cited to FDA.

The present-tense FDA facts, stamped to source — what Category 2 means today, and what the FDA's 2026 advisory-committee agenda does and does not change.

## 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, listed as bulk drug substances "being considered for inclusion on the 503A Bulks List" [18]. The same agenda also lists BPC-157, KPV, and MOTS-C. That places TB-500 squarely inside an active FDA evaluation, and the access picture may expand in 2026.

Read that carefully, because the wording matters. Being on a PCAC agenda is a *scheduled evaluation and discussion* — not a listing decision, not a reclassification, and not a change in current status. A PCAC discussion is advisory; FDA decides inclusion on a final bulks list through rulemaking, informed by but not bound to the committee. The meeting is a step in evaluation, and its outcome is unknown. Nothing here should be read as a result that has already happened.

## Is TB-500 FDA approved?

Is TB-500 FDA approved? No. The current, FDA-citable fact is that FDA lists this 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 nominated substances, citing 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.

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 — it has no FDA-approved therapeutic indication [17]. FDA approval of a finished drug is a separate question from whether a bulk substance may be used in compounding; on both questions, the answer for TB-500 today is no.

## What FDA 503A Category 2 means

Under the Federal Food, Drug, and Cosmetic Act, compounding runs through two sections. Section 503A covers traditional, patient-specific compounding by state-licensed pharmacies and physicians, generally under a valid prescription for an individual patient. Section 503B covers FDA-registered "outsourcing facilities" that may compound larger batches under cGMP-style oversight [16]. 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 the relevant FDA bulks list; substances not yet listed are evaluated through a public nomination process with input from PCAC [16].

FDA's interim policy sorted nominated substances into categories. Category 1 substances are covered by FDA's enforcement-discretion policy while under evaluation. Category 2 substances are those FDA identified as raising significant safety risks; they are not covered by that discretion, and FDA stated it would consider taking action against a compounder for compounding with a Category 2 substance [16]. On January 7, 2025, FDA finalized a revised interim policy under which it no longer places newly nominated substances into these numbered categories — but substances already in Category 2 are not afforded enforcement discretion even if nominations are updated [16][19]. TB-500 sits in Category 2.

## How legally compounded access works

Here is the lawful pathway, in general terms. 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 (patient-specific) or, for larger volumes, sourced from an FDA-registered 503B outsourcing facility [16].

Telehealth can serve as the front-end channel through which a patient is evaluated and a prescription is issued. It is a route to a licensed-prescriber consultation, not a separate legal status: telehealth does not expand which substances may be compounded and does not remove the need for a legitimate clinical evaluation and a valid prescription [16].

One caveat governs all of it. The compounder may use the requested active ingredient only if that ingredient is eligible under the 503A/503B bulk-substance rules — and a substance FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands [16]. For TB-500, that Category 2 status is the current state of [FDA 503A compounding access](/legal-status). This page is general information about the regulatory landscape — not medical or legal advice, and not an offer to sell or supply any substance.

## Beyond the FDA: WADA and the veterinary context

TB-500 is prohibited in sport. It falls under WADA's prohibited peptide, growth-factor, and tissue-repair categories, and it is detected by LC-MS anti-doping assays — banned in and out of competition for the relevant classes [11]. It has also been encountered as a designer tissue-repair drug in racehorses, which prompted equine anti-doping detection methods; that is a veterinary and doping context, not an approved equine medicine.

A note on what we are not saying. Some commercial and clinic pages have reported a possible early-2026 reclassification of Category 2 peptides, or specific dates on which TB-500 was "removed" from Category 2. Those claims could not be confirmed from an authoritative FDA source, and the most candid of them acknowledge the formal reclassification is still pending [17][18]. We state the status as Category 2 — the last FDA action confirmable from FDA.gov — and treat any further change as unconfirmed until FDA publishes it.

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The TB-500 record inked panel by panel on blueprint stock — the Ac-LKKTETQ fragment stamped apart from the full-length thymosin beta-4 it is sold as, the empty human-trial panel left visible, and the FDA 503A status struck first; no clinic at the press and nothing here priced or dispensed.