TB-500

TB-500 is a lab-made chain of seven amino acids ^[6]. Amino acids are the building blocks of proteins. The chain copies a small part of thymosin beta-4, a protein the body makes, with one small chemical change at its start ^{[6] [16]}. Thymosin beta-4 has 43 amino acids, so TB-500 is a short piece of it ^[6].

TB-500 and thymosin beta-4 are not the same substance, even though many websites use the names as if they were ^[6]. TB-500 is part of no FDA-approved drug and has no official quality standard ^[6]. Websites promote it for injury recovery, tendons, muscles, wounds, hair growth and many other uses ^[6]. Sport testing labs look for it because athletes and racehorses may be given it ^{[6] [16]}.

TB-500 is in limbo: FDA lists it among the Category 2 substances whose nominations were withdrawn, and it has not added it to Category 1 ^{[1] [2]}. That is not approval, and it does not make compounding lawful. FDA reviewed it as a shot for wound healing, but websites promote it for injury recovery, muscle and much more ^{[5] [6]}. Checked 23 October 2026.

Category 2 is FDA's list of substances that may present significant safety risks. Category 1 is the list of substances pharmacies may use while FDA reviews them ^[3]. The pharmacy that nominated TB-500 pulled its nomination, so it came off Category 2 ^{[1] [6]}. FDA then reviewed it on its own. FDA's scientists found no study of TB-500 in people and advised against adding it to the list ^{[6] [8]}.

On 23 July 2026, FDA's Pharmacy Compounding Advisory Committee met on TB-500 ^{[4] [5] [7]}. News and legal reports say it voted 8 to 6, with 1 member abstaining, to recommend adding TB-500 to the list ^{[11] [12] [21]}. FDA's meeting page does not show the vote ^[5]. A committee vote is only advice ^[21]. FDA decides by writing a rule, after public comment ^{[12] [22]}.

Until then, a pharmacy that makes TB-500 is outside federal law ^{[3] [11]}. Selling it for people to use is also illegal, even when the label says it is for research only ^[9].

The evidence grade is animal-only: FDA found no study of TB-500 in people ^[6]. One rat study, published in July 2026, tested a substance it calls synthetic thymosin beta-4 (TB-500) ^[14]. Its summary does not say whether that was the seven-amino-acid piece. Most other studies cited for TB-500 used a different molecule. They are named below as borrowed evidence.

The rat study: in rats whose Achilles tendon was cut and repaired, shots into the belly cavity gave stronger, more orderly tendons after four weeks ^[14]. The authors call this an early result that needs more study ^[14]. In a lab test on skin cells, TB-500 itself did not help a scratch close ^[6].

Borrowed evidence: a 2003 mouse study tested thymosin beta-4 and a seven-amino-acid piece of it on skin wounds, and both sped healing ^[15]. That piece lacks TB-500's chemical change, so FDA says its results do not carry over to TB-500 ^[6]. A review reports that full-length thymosin beta-4 sped healing in animals and in two trials in people with skin ulcers ^[18]. In 9 people with severe dry eye, thymosin beta-4 eye drops eased symptoms ^[19]. In healthy volunteers, thymosin beta-4 given into a vein caused only mild or moderate problems ^[20]. The last three used the whole protein, not TB-500. None of these results is evidence for TB-500 ^[6].

There is no legal way to get TB-500 in the US today ^[6]. No approved drug contains it, here or in ten other countries FDA checked ^[6]. A pharmacy may use a substance with no official quality standard only if it is in an approved drug or on the federal list. TB-500 is neither ^{[3] [6]}. That could change if FDA adds it by writing a rule after the committee vote ^{[11] [12]}.

FDA found no clinical study of TB-500 in people ^[6]. Trials of full-length thymosin beta-4 test a different molecule, so they are not listed here. Any open TB-500 trial would appear in the trials block below, with the date the official registry was last checked.

People who use TB-500 get it in three main ways ^{[6] [9]}. The first is online sellers that label it for research use only. FDA has warned a seller of TB-500 that this label does not make it legal to sell a drug meant for people ^{[9] [13]}. The second is pharmacies. Two websites say they get TB-500 from a compounding pharmacy, though FDA found no pharmacy that markets it ^[6]. The third is websites where people book an online visit to discuss using it ^[6].

In all three, nobody checks what is in the product the way FDA checks an approved drug. A lab found that TB-500 products bought online did not always hold what they claimed ^[17]. FDA found two reports of problems with a TB-500 and BPC-157 blend, with no assessment of harm ^[6]. FDA does not get every report of harm, especially for compounded products, so these files cannot show how often harm happens ^[6].