# An absent human clock for TB-500 half-life

> The clock missing from TB-500 half-life — No validated human half-life exists for the TB-500 fragment. Full-protein pharmacokinetics and horse detection work do not supply one or a dosing plan.

**The clock question**

No one has measured a sound human half-life for TB-500.

## What is the half-life of TB-500?

There is no validated human pharmacokinetic half-life for the Ac-LKKTETQ fragment. Half-life is the time a measured amount takes to fall by half. Its value comes from measurements of a particular substance by a particular route. Changing either calls for fresh measurements.

The [human intravenous pharmacokinetic work](https://pubmed.ncbi.nlm.nih.gov/20536472/) used full-length thymosin beta-4. Its half-life increased with dose. That finding does not provide a number of hours for the smaller TB-500 fragment or for another route.

I distrust an exact hour count here more than a plainly missing one. It can look authoritative while silently changing the molecule. The evidence does not establish how long TB-500 stays in a person's system, and it does not yield a validated dosing interval.

## The horse assay was built for detection

The [horse blood-and-urine analysis](https://pubmed.ncbi.nlm.nih.gov/23084823/) detected TB-500 and its metabolites for doping control. A metabolite is material left after a substance breaks down. Detecting that material serves an anti-doping investigation. Measuring the fragment's half-life in humans would require human pharmacokinetic work.

I appreciate how modest the assay's purpose is. It can establish the presence of a substance without establishing a useful duration of effect in people. Detectability, time in circulation and a recovery benefit are not interchangeable clocks.

The [sports prohibition](/legal-status) therefore does not depend on having a human dosing timetable. The ban and the missing pharmacokinetic study can both be true.

## The stroke experiment defeats more-is-better

In the [embolic-stroke dose-response experiment](https://pubmed.ncbi.nlm.nih.gov/25060418/), male Wistar rats received full-length thymosin beta-4 intraperitoneally at 2, 12 or 18 mg/kg. Neurological function improved at 2 and 12 mg/kg; 18 mg/kg brought no significant benefit. The modeled optimum, approximately 3.75 mg/kg, was an estimate rather than a tested amount.

I reject the casual arithmetic of “more peptide, more repair.” Even within that one animal model, the response did not behave that way. None of these rat amounts supplies a human TB-500 recommendation.

The [mdx mouse muscle experiment](https://pubmed.ncbi.nlm.nih.gov/20126456/) used 150 µg of the full protein intraperitoneally twice weekly for 6 months and produced more regenerating fibers without significant strength improvement. That is a study regimen reported as a study regimen, with an outcome attached. It is not a schedule to copy.

## TB-500 dosage is not hidden between those numbers

The [rat wound paper](https://pubmed.ncbi.nlm.nih.gov/10469335/) and the stroke experiment differ in tissue, route and outcome. The wound paper's cell assays found activity with as little as 10 pg; that amount describes the cell assay's keratinocyte-migration observation. A range assembled from these experiments would be a range of different questions.

No completed controlled human trial has established a TB-500 dose for an injury. Community “loading” and “maintenance” routines are anecdotal practices without published clinical validation, and [the sports-medicine review's human-safety gap](https://pubmed.ncbi.nlm.nih.gov/41966639/) cannot be filled with conversions from animal body weight.

A number accompanied by a route and an animal is useful research context. Remove those particulars and it begins to resemble a prescription without earning one.

**Who decides the number**

## Where these figures stop, and what takes over

**Clinician-set, not reader-set**

![Prescription TB-500 from mypromise.com, pictured on a Promise Peptides card with its Rx only label](https://mypromise.com/media/products/tb-500.png)

*The pictured TB-500 preparation from Promise Peptides (mypromise.com) is marked Rx only. The label doesn't guarantee a prescription.*

Nothing above is a regimen. Every figure on this page is a dose given to an animal to answer that study's question, and no validated human dose exists for the TB-500 fragment to convert them into. The number a person would actually need is simply absent from the literature, and no amount of arithmetic on milligrams per kilogram will manufacture it.

For a prescription decision, the relevant step is a clinical review of the person, not a conversion of the animal figures. At mypromise.com, Promise Peptides has begun prescribing TB-500; the U.S.-licensed prescriber examines the individual request and can withhold a prescription. Patients outside the United States are excluded. State rules and the particular treatment determine what can be offered. This compounded medication has no FDA approval. Which substances may be compounded at all is a separate question, and for TB-500 it is the one the [TB-500 legal status](/legal-status) page tracks.

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A developer-console reading of the TB-500 record — the actin-binding fragment logged against its studies, with the full-length thymosin beta-4 caveat flagged in every diff, no clinic behind the terminal and nothing here prescribed or sold.