What TB-500 is
TB-500 is a common name. FDA's review says it isn't a United States Adopted Name, the kind of unique name a drug sold in the United States is given. The review says TB-500 free base is understood today to be a synthetic fragment of thymosin beta-4 that is seven amino acids long, amino acids 17 to 23 of it, with an acetyl group on the leucine at the front, written Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH. The review gives its formula as C38H68N10O14 and its molecular weight as 889.01 g/mol, and gives 949.1 g/mol for the acetate salt. It says the free base is reported as a white to off-white solid that is soluble in water.
Thymosin beta-4 itself is the full-length peptide, 43 amino acids long. FDA's review says several websites often use the two names interchangeably, and that thymosin beta-4 and TB-500 are not the same substance. It also says FDA has encountered multiple salts and derivatives, including different active moieties, sold commercially under the TB-500 name, and it calls naming like that a safety risk, because patients may be dosed with a different substance than the physician ordered. This page can't tell you which of those a vial holds. The calculator only works from the amount on the label.
Where it stands with the FDA
TB-500 isn't approved by the FDA, and the agency says it isn't a component of any FDA-approved drug. It was nominated for compounding, and the nomination was withdrawn. FDA says it was unclear whether the nomination was for TB-500 free base or TB-500 acetate, so it reviewed both on its own initiative.
The review looked at one use, wound healing. FDA says its search didn't identify data, such as clinical studies, on the use of TB-500 in humans, and that its literature search found no articles in which TB-500 was given to humans. It didn't identify nonclinical toxicity studies either. It says the potential safety risks of using TB-500 in humans are unknown, and that there's a lack of evidence to evaluate whether TB-500 products work for wound healing.
The review concluded that the criteria weigh against putting TB-500 on the list of substances pharmacies may compound with, and proposed not adding it. The reasons it gives include that TB-500 isn't well characterized physically and chemically, and concern about immune reactions to it in an injection. On the first point, the review says the certificate of analysis it found in the public domain for the free base didn't test or control assay, impurities, bacterial endotoxins or aggregates. The briefing document also says FDA won't issue a final determination until the committee's input has been considered and all reviews have been finalized.
FDA's page on substances that may present significant safety risks, current as of April 22, 2026, lists "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" among the substances that were previously in category 2 and were withdrawn by their nominators. Category 2 is where FDA put substances that may present significant safety risks. The page says compounded drugs containing it may pose risk for immunogenicity for certain routes of administration, and that FDA has not identified any human exposure data on drug products containing it. It adds that FDA lacks important information about any safety issues it raises, including whether it would cause harm if administered to humans.
FDA put TB-500 on the agenda of its Pharmacy Compounding Advisory Committee for July 23, 2026. The meeting page had no minutes posted as of October 2026, so this page doesn't report a vote.
The strength in the record
The product described in the nomination was a 3 mg/mL lyophilized powder for injection under the skin or into a muscle. FDA's review also says several websites were found offering TB-500 products including a 2 mg, 3 mg, 5 mg, 10 mg and 15 mg powder for reconstitution, and that those websites state the products are intended for research use only. The 5 mg vial in the table below is this page's own example. It isn't a vial size from the nomination.
| Strength in the record | Water for a 5 mg vial | One unit holds | 10 units hold |
|---|---|---|---|
| 3,000 mcg/mL | 1.667 mL | 30 mcg | 300 mcg |
Add that much water to a 5 mg vial and it comes to that strength. Any other amount of water works too. It only changes how many units the same dose takes up.
Storing TB-500
The storage figures in FDA's review are about the bulk substance, and they are reports the review repeats. For TB-500 free base it cites a product data sheet that says to store it in a sealed container, away from moisture and light and under nitrogen, at -80°C for 2 years or -20°C for a year as a powder, and at -80°C for 6 months or -20°C for one month in solvent. The review's summary is that the free base is reported to be stable below -20°C under those conditions.
For TB-500 acetate the review repeats two figures. The certificate of analysis sent in with the nomination recommends 2-8°C, in a refrigerator or a freezer, in a sealed container. Information from the public domain recommends below -15°C, protected from light in a tightly closed container. The review also says that how stable a peptide stays depends heavily on how the finished product was made.
There's no approved label for TB-500, so nothing official says how long a mixed vial keeps.
TB-500 dosage calculator questions
How do I turn a TB-500 dose into syringe units?
Divide the dose by the concentration to get millilitres, then multiply by 100. A 5 mg vial mixed with 2 mL is 2.5 mg/mL, so one unit on an insulin syringe holds 25 mcg and ten units hold 250 mcg.
How much bacteriostatic water goes in a 5 mg vial of TB-500?
There's no single right amount. The water only sets the concentration, and the amount of TB-500 in the vial stays the same. With 5 mg, 1 mL makes 5 mg/mL, 2 mL makes 2.5 mg/mL and 3 mL makes 1.667 mg/mL. Choose the amount that puts your dose somewhere between about 10 and 40 units, where it's easiest to read.
Is TB-500 approved by the FDA?
No. FDA says TB-500 isn't a component of any FDA-approved drug. It reviewed TB-500 for use in compounded drugs, concluded the criteria weigh against it and proposed not adding it to the list pharmacies may compound from, then put it on an advisory committee's agenda for July 23, 2026.
Does this page tell me how much TB-500 to take?
No. There's no FDA-approved TB-500 product, and FDA says its search didn't identify clinical studies of TB-500 in humans, so this page has no approved dose and no trial dose to report. The dose box starts empty for that reason, and the chart only converts.
Is TB-500 the same as thymosin beta-4?
No. FDA's review says thymosin beta-4 and TB-500 are not the same substance. It describes TB-500 as a synthetic fragment seven amino acids long, amino acids 17 to 23 of thymosin beta-4, which is 43 amino acids long.
Is TB-500 on the anti-doping prohibited list?
FDA's review says it is. It says TB-500 is on the World Anti-Doping Agency's list of prohibited substances, which the review's authors looked up on February 15, 2024.
More peptide calculators by name
The same instrument, set up one peptide at a time. For any other vial, use the peptide reconstitution calculator.