TB-500 Tracker: Logging a Peptide With Borrowed Numbers

Is TB-500 the same as thymosin beta-4?

No, though the names are often used loosely. Natural thymosin beta-4 is a 43-amino-acid protein, and the recombinant version tested in a phase 1 study, called NL005, had 44.^[4] The FDA's bulk substances page lists an item it calls thymosin beta-4, fragment, in its nominated-and-withdrawn section, and it says it has not identified any human exposure data for drug products containing that fragment.^[1] So the label TB-500 can point to a fragment, while the human numbers that exist belong to the full-length protein. That mismatch is the main reason a TB-500 tracker has to be honest about its limits. PepTrac lets you add a compound called TB-500, record every dose and vial, and see an estimate, but it flags that the half-life behind the estimate is borrowed. It does not sell TB-500 and does not suggest a dose.

Thymosin beta-4

A 43-amino-acid protein. Phase 1 data exists only for a recombinant full-length version given intravenously.^[4]

TB-500

A name sellers use, usually for a fragment. The FDA lists the item as thymosin beta-4, fragment.^[1]

NL005

The recombinant human thymosin beta-4 tested in healthy volunteers, with a half-life of 0.5 to 2.08 hours.^[4]

Assumed peak time

PepTrac's stand-in for time to peak when none is on record: 0.2 times the half-life, captioned peak est. on the chart.

Wide band

A wider shaded range, drawn when the half-life came from an intravenous study.

Is TB-500 FDA-approved?

No. As of October 2026 the FDA lists thymosin beta-4, fragment, in its bulk drug substances section for items that were nominated for compounding and then withdrawn. The page, current as of April 22, 2026, flags a risk of immunogenicity from aggregation and peptide-related impurities, and states that the FDA lacks important information on safety issues.^[1] According to a summary by the law firm McDermott Will & Schulte, the FDA's Pharmacy Compounding Advisory Committee voted 8 to 6, with 1 abstention, on July 23, 2026 to recommend both TB-500 and BPC-157 for the 503A bulk drugs list. The vote is advisory, and the FDA would still need to finish rulemaking.^[2] A recommendation to list a substance for compounding is not an approval and not a finding that it works. These pages change, so recheck the FDA before relying on this paragraph. It reflects what the cited sources said on October 3, 2026.

Is TB-500 prohibited in sport?

Yes. The U.S. Anti-Doping Agency's summary of the 2018 World Anti-Doping Agency Prohibited List states that thymosin-beta-4 and its derivatives, such as TB-500, were added as examples of prohibited growth factors under section S2.3.^[3] That page describes the 2018 change, so athletes should read the current list for the current wording instead of relying on it. Anti-doping rules apply to the athlete under their own program, not to an app, and a tracker does not make a substance allowed or detectable. PepTrac does not check any prohibited list for you, and it is not a compliance tool of any kind. If you compete under an anti-doping program, ask your governing body or your national anti-doping organization about any substance before you use it, because the list is revised each year. Logging a dose in an app changes nothing about that.

What half-life data exists for TB-500?

The only human half-life data PepTrac found is for recombinant full-length thymosin beta-4, not for the TB-500 fragment. A phase 1 study in healthy volunteers in China gave NL005 by intravenous injection and reported a half-life of 0.5 to 2.08 hours across dose groups, in 54 volunteers in the single-dose trial and 30 in the multiple-dose trial.^[4] It was published in the Journal of Cellular and Molecular Medicine. It did not study subcutaneous injection, and it did not study the fragment. PepTrac's catalog uses 1.3 hours for TB-500, which sits inside that range, and it has no time-to-peak value because the study supplies none. Those gaps are why the app draws a wide band. If you have a better-sourced number, you can enter your own half-life for the compound and the curve will use it instead.

Why does PepTrac show a wider band for TB-500?

Two borrowed inputs make the estimate less certain, so the app widens the range. Normally the shaded band reruns the curve with half-life and peak time each changed by 20 percent. For TB-500 the half-life came from an intravenous study, so the half-life sweep widens to 35 percent. With no peak time on record, the app assumes 0.2 times the half-life and sweeps that by 50 percent, and the chart caption reads peak est. For an example 2 mg entry, the estimate is 0.83 relative units at 2 hours, with a range of 0.44 to 1.11. At 6 hours it is 0.10, range 0.02 to 0.23, and at 12 hours 0.004, range 0.000 to 0.021. The amount is an arithmetic example, not a dose recommendation. The band at 2 hours is almost as wide as the estimate, and that width is the honest result. The range is a sensitivity range, not a statistical confidence interval.

What should a TB-500 log include?

Because so little is established about TB-500, the record is the most reliable thing you can hold. Write down the date and time, the amount, the injection site, the vial and its reconstituted date, the seller or source, the lot or batch note, and anything you want to raise with a clinician. The FDA's concerns about aggregation and peptide-related impurities in compounded versions are a practical reason to keep source and lot records, so you can tell one vial from another if a question comes up.^[1] PepTrac stores the dose, time, and site with each entry, shows your most recent sites on a body map, and tracks each vial's fill percentage and days left. It stores a reconstituted date you enter, but it does not count down or flag any expiry. It has no dedicated side-effect log, so keep symptom notes separately. PepTrac does not suggest a TB-500 dose or schedule.

To log TB-500 next to another compound, read the peptide stack tracker page. For vial arithmetic, see how to reconstitute peptides.