PLAIN ANSWERS FROM STUDIES AND FDA PAGES
A sore spot brings questions: plain TB-500 answers
Start with what hurts, what you've heard about TB-500, or the rule that worries you. Each answer identifies whether the work involved people, live animals, or loose cells.
What the compound is and how it may move repair cells
What does TB-500 do in the body?
TB-500 is built in a lab from seven protein building blocks. Those blocks are numbered 17–23 in thymosin beta-4 [1].
It weighs about 889 daltons versus 4963 daltons for the full protein; a dalton is a tiny unit of weight. The gap shows they aren't the same thing, but it doesn't show what either will do in you.
In TB-500, what do TB and the name TB-500 mean?
TB means thymosin beta. TB-500 is a research and animal-care name for a section of thymosin beta-4 made in a lab [5].
The number is a seller's label. The seven-part section uses blocks 17–23 and can hold actin, a protein that helps your cells change shape and travel.
What changes have TB-500 researchers looked for?
Researchers studied wounds, blood vessels, hearts, brains, hair, swelling, and scars in animals or dishes of cells [5]. Nearly all got full thymosin beta-4 instead of TB-500, so the work doesn't prove healing for you.
How may TB-500 change the way cells move?
TB-500 can keep one loose actin part from joining another. The lab writes one protein holding one part as 1:1 [1].
Actin is a protein inside your cells. It helps them rebuild inner support and move, but human tests haven't proved that the small piece copies thymosin beta-4.
What TB-500 research found in wounds, organs, and hair
What did TB-500 change in swelling tests?
Full thymosin beta-4 lowered IL-8, the lab's name for a chemical call that brings immune cells and swelling [7]. Eye tissue changed in a similar way [8], but no fair test in people has shown that the small seven-part piece calms swelling for you.
What did TB-500 wound studies actually show?
Rats given full thymosin beta-4 grew 42% more skin cover at 4 days and up to 61% more at 7 days. Their wounds also shrank and made more collagen, the protein that strengthens skin [3].
Eye drops called RGN-259, made from full thymosin beta-4, helped human eyes and dry eye [16]. Neither finding tells you about the small piece.
What did TB-500 change in animal hearts?
Researchers shut one vessel that fed mouse heart muscle. Full thymosin beta-4 then helped heart cells live and the heart work [2].
In pigs, full thymosin beta-4 failed a test of lost and restored blood flow [10]. The animal work can't predict your heart result.
What did TB-500 change after a rat stroke?
After a stroke, rats moved better. They got 2 and 12 milligrams of full thymosin beta-4 for each kilogram of the rat's weight.
At 18 milligrams per kilogram, the rats gained no help. About 3.75 milligrams per kilogram looked best in that rat test [4], and the small piece wasn't tested.
Can TB-500 grow blood vessels that may feed a tumor?
With full thymosin beta-4, low oxygen had 1 clear effect: blood-vessel cells started moving and growing [5]. Extra vessels might mend your tissue or feed a tumor, but that finding doesn't prove that TB-500 causes cancer.
What did TB-500 change in animal hair growth?
Tiny measured amounts of full thymosin beta-4 stirred cells at the hair root and hair growth in rats and mice [5]. No sound human hair study has used TB-500, so your hair may not follow the animal result.
How does TB-500 differ from BPC-157, another lab-made protein piece?
TB-500 comes from thymosin beta-4. It holds actin, which helps your cells change shape and move.
BPC-157 copies part of a protein found in stomach fluid [1]. In 2026, a Sports Med review called the animal findings hopeful but found little proof about your safety [11].
What repair signs didn't improve useful healing
What did TB-500 change after muscle tears or exercise?
In mice with weak muscles, full thymosin beta-4 drew young muscle cells and raised rebuilding fibers WITHOUT better strength, heart function, or scars [5]. Thymosin beta-4 left the mice just as weak, and no study in people proves that TB-500 will help your recovery.
What human trials have tested the small TB-500 piece?
No completed fair test in people has used the TB-500 seven-part piece for any purpose [6]. Phase 1, the first step that checks safety, used full thymosin beta-4 by vein; eye tests used drops of full thymosin beta-4 called RGN-259, and neither can promise that the small piece will heal you [16].
When did wound changes appear in TB-500 studies?
No human study tells you when TB-500 healing would start. Full thymosin beta-4 raised rat skin cover 42% at 4 days and up to 61% at 7 days against salt water [3], but your healing time can't come from a rat.
What did TB-500 change in tendons and ligaments?
In tendon and ligament work, full thymosin beta-4 reduced scar-making cells, moved repair cells, and grew small blood vessels [5]. The animals got the whole protein, so the work can't say whether TB-500 would help your tendon or ligament.
What we know about immunity, cancer, and long use
What could TB-500 do to your immune system?
Controlled human safety work doesn't tell you how TB-500 affects your immune system. Lab-dish work found that full thymosin beta-4 lowered IL-8, the lab's name for one chemical call tied to swelling [7].
FDA raised a different concern: your immune system might react against the small piece. That concern helped place the small piece in Category 2, its warning group for raw drug ingredients [21].
What is the tumor concern with TB-500?
High amounts of full thymosin beta-4 appear in several cancers. The protein helps cells travel and blood vessels grow [5], which a tumor could use, but that worry doesn't prove TB-500 causes cancer in you.
What unwanted TB-500 effects are actually known?
Controlled human studies give you no list of TB-500 side effects [6]. Tumor and blood-vessel work on thymosin beta-4 [5], plus doubt about what research powder holds and how clean it is [17], are the main worries; online reports aren't trial results.
What is known about long-term TB-500 safety?
Long-term human safety facts for TB-500 don't exist. During Phase 1, the first safety check, people got up to 1260 milligrams of full thymosin beta-4 by vein over 14 days without a problem that stopped dosing [6], but that brief test can't settle your long-term risk [11].
What FDA and sport rules allow now
What happens if a tested athlete uses TB-500?
The World Anti-Doping Agency sets the drug-test ban for TB-500 and thymosin beta-4 in the matching sport groups, both during and outside a contest [13]. Tests can find the small piece from both people and horses, so the rule matters if you're tested.
What has FDA approved TB-500 to treat?
Nothing. TB-500 has no FDA approval as a human drug [21], while licensed clinicians can assess requests for prescription care. FDA records the ingredient's nomination as withdrawn [20]; that record neither authorizes compounding nor makes TB-500 a Category 1 ingredient.
What does the law currently allow for TB-500?
FDA hasn't approved TB-500 and put the seven-part piece in Category 2 for possible major safety risks [21][20]. Withdrawal of the nomination is not permission to compound it or a place in Category 1 [20]. Prescribing now happens after a licensed U.S. clinician's case review, which can end in a declined request; state and treatment restrictions still apply. FDA drug approval does not come with compounding.
Sport rules are separate and also ban the small piece [13]. Neither rule tells you that the substance is safe or works.
Can a pharmacy make TB-500 for one person?
A pharmacy making a drug for one named patient must first confirm that the raw ingredient is allowed [22]. The FDA safety label is part of that check.
FDA's 2023 major-risk listing stood in the way of that named-patient work. FDA marks its page current through April 22, 2026; it records the TB-500 nomination as withdrawn and no longer lists the ingredient in Category 2 [21], and the withdrawal does not authorize compounding. A clinician's decision to prescribe and a pharmacy's ingredient check are separate steps [22].
What is FDA's current status for TB-500?
On September 29, 2023, FDA placed TB-500, the small thymosin beta-4 piece, in Category 2 under its named-patient pharmacy law for possible immune reactions and missing safety facts [21]; its page, current as of April 22, 2026, lists the request as withdrawn instead. The July 23–24, 2026 agenda named "TB-500 (free base)," one lab form, and "TB-500 acetate," another form of the same ingredient; FDA has published no decision from that meeting [19].