Choose one of 19 peptides with a published human half-life, or type in your own. Pick a spacing and the chart shows one dose fading out, then repeated doses stacking up until they level off.
With a half-life of about 7 days, 50% of each dose is still in circulation when the next one arrives. Each new dose lands on top of that leftover, so levels climb for about 5.1 weeks until the amount cleared between doses equals one dose. After that the curve repeats between the two amber lines.
Simplified one-compartment model: each dose enters the blood at once and clears at a fixed rate. Injected peptides absorb over hours to days, which lowers and delays the real peaks. Levels are shown relative to one dose, not as amounts. This is not a dosing schedule.
A half-life close to the dosing interval means a large share of each dose is still circulating a week later. These are the long-acting compounds in the database, modeled at one dose a week.
Semaglutide was built to last. A fatty-acid side chain makes it stick to albumin in the blood, which keeps it from being filtered out by the kidneys and stretches its half-life to about 7 days. On a weekly schedule 50% of each dose is still there when the next goes in.
That is why the approved labels step the dose up no faster than every 4 weeks. Four weeks is about four half-lives, enough for the level to settle near its new plateau before the next increase. The same math explains why side effects after a dose increase can take a few weeks to settle.
It works in reverse after stopping: about five half-lives, roughly five weeks for semaglutide, before 97% has cleared.
The scale is logarithmic so a one-minute half-life and a two-week half-life fit on the same line. Unmodified natural peptides clear in minutes. Drugs engineered to last, like semaglutide, stay for days.
Values are from each peptide's profile, which cites the source study or label. Where a profile gives a range, the bar shows the midpoint. Not listed: the 33 compounds with no measured human half-life.
The model puts each dose straight into the blood. A shot under the skin is absorbed over hours to days, so real peaks are lower and later than the curve shows. Semaglutide, for example, reaches its peak 1 to 3 days after the injection.
For most research peptides nobody has measured how long they last in people. Where only rat or dog data exists, this tool does not offer the compound, because animal half-lives do not carry over reliably.
Kidney and liver function, body size, the injection site and the formulation all shift the real half-life. Published values are averages from trial participants.
A peptide can leave the blood in minutes and still trigger something that lasts hours, such as a release of growth hormone. The curve tracks the molecule, not what it does.
Want half-life next to evidence grade and legal status? Compare peptides side by side.
When a trial reports how long a peptide lasts in people, or a label changes, you get a short summary and the link. Weekly at most.