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

The current FDA status, stated plainly

TB-500 legal status begins with one citable fact. The U.S. Food and Drug Administration 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 its list of nominated bulk drug substances, citing concerns including potential immunogenicity for certain routes of administration and a lack of important safety information ^[16]. FDA's own list entry establishes the relationship: TB-500 is the LKKTETQ fragment associated with thymosin beta-4.

Two consequences follow directly from Category 2. First, as a Category 2 substance, TB-500 is not within FDA's enforcement-discretion policy for 503A compounding — the policy that covers certain substances still under evaluation does not extend to it. Second, TB-500 is not an FDA-approved drug; it has no approved therapeutic indication. Those are the present-tense facts, cited to FDA, and they are the floor this page stands on.

What may change in 2026 — under active review, not yet decided

There is genuine forward momentum, and it is worth stating with its hedges intact: access to TB-500 is under active FDA review and may expand in 2026. The anchor for that statement is concrete. "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" — the same agenda that lists BPC-157, KPV and MOTS-c ^[17].

Read that for exactly what it is. A scheduled PCAC discussion is an evaluation step — a public advisory meeting where candidates for the bulks list are considered. It is not a listing decision, not a reclassification, and not a change in current status. PCAC advises; FDA decides separately, through rulemaking. No outcome should be assumed or dated. What the agenda confirms is that TB-500's evaluation is ongoing — which is consistent with the present standing, not a departure from it. The momentum is real; the result is pending.

How legally compounded peptide access works

Compounding in the United States is governed by two sections of the Federal Food, Drug, and Cosmetic Act. 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. 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 ^[16].

In practice the lawful pathway runs in order: a patient is evaluated by an appropriately licensed prescriber — in person or through a compliant telehealth encounter — who determines whether a compounded preparation is clinically appropriate; if it is appropriate and lawful, the prescriber issues a valid, patient-specific prescription; that prescription is dispensed by a state-licensed 503A compounding pharmacy or, for office or batch use, sourced from an FDA-registered 503B outsourcing facility ^[16]. Telehealth is one front-end channel for the prescriber-evaluation step — a route to a consultation and prescription, not a separate legal status, and it does not expand which substances may be compounded.

The ingredient-eligibility caveat is the part that governs TB-500 specifically. A compounded preparation may lawfully be made only when its active ingredient is permitted under the 503A/503B framework, and a substance FDA has flagged for significant safety risks is not eligible for routine 503A compounding while that status stands ^[16]. That is the current constraint on the LKKTETQ fragment. This page is general information about the regulatory landscape — not medical or legal advice, and not an offer to sell or supply any substance.

Is TB-500 FDA Approved?

No. TB-500 is not approved by the FDA and has no approved therapeutic indication. FDA lists it 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 — so it is also not within FDA's enforcement-discretion policy for 503A compounding ^[16]. FDA approval of a finished drug is a separate question from compounding eligibility, and neither applies here.

What is the FDA 503A status of TB-500?

TB-500 sits in FDA's 503A "Category 2" — nominated bulk substances that FDA identified as potentially presenting significant safety risks — effective with the September 29, 2023 nominated-substances update, citing potential immunogenicity for certain routes and a lack of important safety information ^[16]. Category 2 substances are not covered by the enforcement-discretion policy that applies to Category 1. TB-500 is also on the July 23-24, 2026 PCAC agenda as a candidate being considered for the bulks list — a scheduled discussion, not a decision ^[17].

Can you get TB-500 from a compounding pharmacy?

Lawful compounding requires a valid, patient-specific prescription from a licensed prescriber and an active ingredient eligible under the 503A/503B framework ^[16]. Because FDA placed TB-500 in 503A Category 2 as a substance that may present significant safety risks, it is not eligible for routine 503A compounding while that status stands ^[16]. This is general regulatory information, not advice on obtaining any substance, and not a route around FDA restrictions.

Is TB-500 legal?

The accurate answer is layered. TB-500 is not an FDA-approved drug and is sold by research suppliers for laboratory use only; FDA placed the LKKTETQ fragment in 503A Category 2, so it is not within FDA's enforcement-discretion policy for compounding ^[16]. It is prohibited in sport by WADA and is classified as a prescription medicine in some jurisdictions. "Legal" therefore depends entirely on context — approval, compounding eligibility, sport, and jurisdiction are separate questions, and this page describes the regulatory landscape rather than offering legal advice.

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. The prohibition is a sport-governance status, distinct from the FDA compounding question, and it applies regardless of formulation ^[13].

Why is TB-500 used in racehorses?

TB-500 has circulated as a veterinary and designer preparation in equine sport, which prompted the first LC-MS detection methods in horse plasma and urine — with limits of detection around 0.01-0.02 ng/mL — to control its misuse. It is a prohibited substance in regulated competition. The equine-detection history is part of why anti-doping science characterizes the heptapeptide so precisely, even though human pharmacokinetic data for the fragment do not exist ^[13].