Peptide and compound half-lives, compared

A half-life is the time it takes for the amount of a compound in your blood to fall by half. It is the single most useful number for working out how often to dose something — and the single most commonly misread one.

Two things follow from it directly. Dose repeatedly and the compound accumulates until intake and clearance balance, which takes roughly four to five half-lives — so a peptide with a five-day half-life is still climbing towards its eventual level three weeks in. Stop, and clearance runs the same course in reverse: four to five half-lives to fall to something negligible. That is why a once-weekly compound forgives a late injection and a twice-daily one does not.

What a half-life does not tell you is how long the effect lasts. BPC-157 clears from plasma in well under an hour; whatever it does to tissue does not stop when the molecule does. The Khavinson bioregulators are measured in minutes and are claimed to act through changes that outlast them entirely. In the other direction, a compound can sit in your blood long after it has stopped doing anything useful. Plasma concentration and effect are different curves, and the table below is only the first one.

Reading the two columns

Half-life is a single number, which makes the table sortable and comparable at a glance. As published is the figure as the source states it, and it usually carries something the number cannot: which ester, which route, which population. Testosterone reads “~8 days (cypionate)” because the ester is doing the work, not the hormone. Winstrol reads “~9 hours (oral), ~24 hours (injectable)” because the same molecule behaves differently depending on how it arrives. Where the two disagree, the published text is the authoritative one — the number is a handle for sorting.

Why some are blank

Almost always because nobody has measured it in humans. Most of the research peptides here have pharmacokinetic data in rats, in cell culture, or nowhere at all. An empty cell is an honest statement about the evidence, and the methodology page explains why the site prefers saying so to filling the gap with a plausible figure.

Turning a half-life into a schedule

The practical question — “if I dose this every three days, where does it settle?” — is arithmetic, and the accumulation calculator does it: put in a half-life, a dose and an interval and it draws the curve to steady state. If the question is instead how much to draw up for one injection, that is the reconstitution calculator, and the reconstitution chart has it worked out per peptide.