Glossary
Half-life
Also called Elimination half-life, t1/2, Plasma half-life
The time it takes for the amount of a substance in the blood to fall by half. It largely decides how often a compound is dosed.
In more detail
A short half-life means levels rise and fall fast, which is why some peptides are taken once or twice a day. A long half-life means levels build up slowly and fade slowly, which is why semaglutide, tirzepatide and retatrutide are taken once a week.
Half-life also shapes how long it takes to reach a stable level when you dose on a schedule, and how long something lingers after you stop. That is the logic behind washout periods and loading doses.
Why it matters
Many half-life figures quoted for research peptides come from animal studies or from no clear source at all. Each compound page on this site shows the half-life with where the number came from.
Related terms
- WashoutTime off a compound so it clears the body before you start something else or measure your baseline. In trials it separates one treatment from the next.
- Loading doseA higher dose at the start of a course to reach a working level faster, followed by a lower maintenance dose.
- TitrationStarting at a low dose and raising it in steps over weeks, so the body adapts and side effects stay manageable.
- CycleA set period of taking a compound, usually followed by a planned break. A protocol might say 8 to 12 weeks on, 4 weeks off.
Peptides where this comes up
Sources
Each source is labeled by where the information comes from. How we label sources
- Reference workBiological half-life(opens in a new tab)
Wikipedia · checked
- Reference workLoading dose(opens in a new tab)
Wikipedia · checked
Updated