TB-500 legal status: FDA entries
The published FDA entries describe several different decisions. A change in one entry leaves the other questions to be answered on their own terms.
FDA approval
TB-500 has no FDA-approved therapeutic indication. The FDA safety-risk page concerns bulk substances considered for compounding, while the 503A framework describes ingredient requirements. Approval of a finished medicine is a separate matter from the eligibility of a bulk ingredient for compounding.
The phrase “under review” gives me particular trouble: it can sound much more conclusive than the paperwork supports. A research result, a nomination and a finished-drug approval each answer a different question.
FDA nomination history
The TB-500 entry entered Category 2 with FDA's September 29, 2023 update. That category covers bulk substances that may present significant safety risks; the stated concerns included potential immunogenicity for certain routes and missing important safety information. On FDA’s page current as of April 22, 2026, the nomination is recorded under “Bulk drug substances nominated but withdrawn,” and TB-500 no longer appears in Category 2. The page retains the safety rationale.
FDA publishes no date for the removal itself. The page's content date provides a dated record of what it says. FDA has not explained how pharmacies should apply its 503A enforcement-discretion policy following that withdrawn nomination, under the bulk-substance framework.
July 2026 agenda
The published July 23–24, 2026 Pharmacy Compounding Advisory Committee agenda named TB-500 free base and TB-500 acetate for consideration for the 503A Bulks List. FDA staff proposed against listing them. FDA has published no record of the committee's votes, so the agenda establishes the evaluation topic without establishing an outcome.
The committee is advisory. A final listing decision requires FDA rulemaking under the 503A process. An optimistic interpretation of that agenda leaves me unconvinced without a published decision.
Compounding requirements
The FDA bulk-substance framework distinguishes ingredient eligibility from the clinical evaluation and prescription process. Patient-specific 503A compounding involves a licensed prescriber and a state-licensed pharmacy; 503B outsourcing has separate requirements. Eligible bulk substances must meet the applicable requirements through a USP/NF monograph, status as a component of an FDA-authorized drug, or the relevant bulks list.
Telehealth can provide the prescriber-evaluation channel. It leaves ingredient requirements in place. For TB-500, the withdrawn nomination still leaves an unanswered question about application of the 503A policy. General explanations of the process cannot decide eligibility for an individual preparation.
Is TB-500 legal?
“Legal” needs a jurisdiction and an activity. In the U.S. record described here, TB-500 has no FDA authorization as a drug, its nomination is withdrawn, and FDA has not resolved the resulting enforcement-discretion question for routine 503A compounding. The withdrawn-nomination entry and 503A rules support those limited statements.
This page provides general regulatory information rather than legal advice. I need FDA’s explanation of the withdrawn nomination to resolve that access question.
Two separate traces
A product listing does not rewrite FDA status
Two traces must not be shorted together: the ingredient's regulatory status and the process by which a clinician reviews an individual patient. After evaluation, Promise Peptides clinicians may prescribe TB-500 through licensed telehealth at mypromise.com; that narrow provider-specific fact does not answer how the withdrawn nomination applies to compounding and does not establish FDA approval. It identifies a clinician-reviewed access path, not a blanket conclusion about compounding eligibility or legality.
Sport and racehorses
TB-500 and thymosin beta-4 fall under WADA's prohibited peptide, growth-factor and tissue-repair categories, with prohibition in and out of competition for the relevant classes. The sports-medicine review discusses the unapproved-peptide context. That prohibition stands separately from U.S. compounding questions.
The racehorse association is also specific. The equine anti-doping study characterized TB-500 and its metabolites in horse plasma and urine after the peptide had appeared as a veterinary preparation. This analytical history explains the name's presence in anti-doping science; it establishes no approved human indication.