CURRENT RULES / 05
TB-500 Legal Status: FDA has not approved the drug
Prescription access to TB-500 involves a clinician's decision. A withdrawn nomination does not grant FDA drug approval or blanket permission for pharmacy mixing.
A 2026 FDA meeting didn't promise a rule change
Did FDA approve TB-500? No; advisory discussion of two TB-500 forms did not grant FDA drug approval [17].
The two TB-500 forms differ in how a lab prepares the same main substance. The FDA calendar records an advisory meeting about those forms [16].
The committee's discussion addressed the 503A list [16]. That list helps decide what a pharmacy may mix for one named patient.
The same notice named BPC-157 and other substances. It said TB-500 might be weighed for the list.
Any permission for pharmacy mixing must come from the applicable substance rules [18]. The meeting notice didn't change access.
The advisers can only give advice [16]. FDA makes the final 503A decision [18].
The calendar documents an advisory discussion, while FDA's current page records a withdrawn TB-500 nomination [16][17]. Neither record establishes FDA drug approval or general permission to compound TB-500.
FDA still lists the fragment among higher-risk substances
Why does FDA list TB-500 as a concern? FDA originally placed TB-500 in Category 2 [17].
Category 2 covers substances that may pose serious safety risks. FDA cited a possible immune reaction and too little safety information.
That entry makes clear which substance FDA means. It names the TB-500 fragment as the short part of thymosin beta-4.
The agency hasn't called TB-500 safe or approved. FDA now puts TB-500 in its nominated-but-withdrawn table, outside Category 2 [17].
The withdrawn nomination leaves two separate questions: pharmacy permission and drug approval. Withdrawal alone gives a patient-specific 503A pharmacy no blanket permission to use TB-500 [17][18].
TB-500 also isn't an FDA-approved drug [18]. The pharmacy rule and drug approval are separate tests.
Research-labelled TB-500 remains on sale outside prescription care. That label does not establish a medicine's safety or FDA approval [17].
The withdrawn entry still carries FDA's safety concerns [17]. The advisory calendar supplies no final FDA listing decision [16][18].
503A serves one patient; 503B makes larger batches
What are the two pharmacy paths? They govern pharmacies that mix medicines.
A 503A pharmacy fills a valid prescription for one named patient. A 503B site may make larger batches and must register with FDA [18].
Neither kind of pharmacy may use any substance it wants. A substance must meet a legal test before a pharmacy may use it [18].
It must appear in an official drug quality book, be part of an approved drug, or appear on FDA's allowed list. FDA once put pending requests into Category 1 or Category 2 [18].
The second group meant greater safety concern. On January 7, 2025, FDA stopped giving new requests those numbered labels.
Substances already in Category 2 didn't gain permission [18]. TB-500's withdrawn nomination does not erase the safety concerns beside its entry [17].
A doctor's prescription can't overrule the substance rule
Can a prescription make the fragment lawful for a pharmacy to mix? No, the substance must also pass FDA's rule.
A mixed medicine begins with a licensed doctor who knows the patient [18]. The doctor checks the person's health and decides whether to issue a valid prescription.
A state-licensed 503A pharmacy may then make medicine for that patient. A 503B site may supply larger batches under stricter checks [18].
The first doctor visit may happen by video [18]. A video visit can't make a barred substance legal.
A real health check still comes first; medicine can be dispensed only with a valid prescription [18]. The substance must also meet FDA's pharmacy rule.
FDA has flagged TB-500 for serious safety risks. TB-500 prescribing at mypromise.com is now part of Promise Peptides' prescription-only care; a licensed U.S. clinician examines the case and chooses whether to write a prescription. A clinician may refuse a request. The route serves U.S. patients alone, and the patient's state and selected treatment constrain the options. Its compounded product has no FDA approval.
Prescribing does not turn the withdrawn nomination into FDA permission to compound [17][18]. Prescribers and pharmacies remain bound by the applicable substance rules [18].
These are broad U.S. rules, not a ruling on your case. A lawyer or your state pharmacy board can answer a personal legal question.
The current FDA list gives these short answers
TB-500 is not an approved drug
Is TB-500 an approved drug? No; FDA lists it as the short piece of thymosin beta-4.
FDA put TB-500 in Category 2 because of possible serious safety risks [17]. The nomination is now withdrawn, while FDA's immune-reaction and safety-data concerns remain [17].
Prescription review and pharmacy rules are separate questions
Mixed medicine needs a valid prescription after a licensed doctor checks the patient. It may come from a 503A pharmacy or a 503B batch-making site [18].
Each substance must still pass FDA's pharmacy rule. A withdrawn nomination alone does not answer whether a particular TB-500 preparation meets that test [17][18].
FDA now records the TB-500 nomination as withdrawn
FDA put the thymosin beta-4 short piece called TB-500 in Category 2. The current entry instead sits with withdrawn nominations [17].
FDA cited possible immune harm and too little safety information. The FDA calendar describes advisory consideration of TB-500, rather than a final listing decision [16].
Tested athletes can't use TB-500
TB-500 and thymosin beta-4 are banned in and out of sport contests [13]. Tests can find TB-500 in horse and human samples.
The ban doesn't show whether the drug helps or harms. It settles the sports rule.
TB-500 remains an unapproved drug
TB-500 has no FDA-approved medical use [17]. Sellers label it for research or animals, not as approved medicine.
The pharmacy rule is a second issue. A prescription does not confer FDA drug approval or settle the separate pharmacy question [17][18].