# TB-500 Legal Status, FDA 503A Category, and Compounding Access > TB-500 legal status: FDA placed the LKKTETQ fragment in 503A Category 2; it is not FDA-approved and is WADA-prohibited. How compounded access works, and the 2026 PCAC review. The access record as a man-page readout: --fda NOT-APPROVED, --503a CATEGORY-2, --wada PROHIBITED, --review SCHEDULED-2026. General information, not legal advice. ## 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]. --- Legit TB-500 runs the thymosin beta-4 literature like a status check: the seven-mer marked present, the full-length protein where the data actually live marked separately, the human-evidence column returning zero, and FDA's standing quoted straight — a console for verifying claims, not a clinic, a pharmacy, or a place anything is sold.