What is peptide half-life?
Peptide half-life is the time the body takes to clear half of a peptide from the blood. After one half-life, half is left; after two, a quarter; after about five, almost none.
It decides how often a peptide has to be taken: minutes-long half-lives need a drip or frequent doses, while a week-long half-life allows a weekly injection.
Peptide half-life chart
Half-lives below come from each product’s label or published human studies. Research peptides without human data are listed as unknown.
| Peptide | Half-life in people | Source type | Typical frequency |
|---|---|---|---|
| Semaglutide | About 1 week | FDA label | Weekly |
| Cagrilintide | About 7 to 8 days | Clinical trial | Weekly (in trials) |
| Retatrutide | About 6 days | Phase 1 trial | Weekly (in trials) |
| CJC-1295 with DAC | About 6 to 8 days | Phase 1 trial | Not approved |
| Tirzepatide | About 5 days | FDA label | Weekly |
| Liraglutide | About 13 hours | FDA label | Daily |
| PT-141 (bremelanotide) | About 2.7 hours | FDA label | As needed |
| Tesamorelin | About 26 to 38 minutes | FDA label | Daily |
| Oxytocin | About 1 to 6 minutes | FDA label | IV drip in hospital |
| BPC-157, TB-500, most research peptides | Unknown in people | No human data | Not approved |
Why do some peptides last a week and others minutes?
Natural peptides are broken down quickly by enzymes and filtered by the kidneys, so most last minutes. Long-acting medicines are engineered to avoid that.
Semaglutide and tirzepatide carry a fatty side chain that binds to albumin, a blood protein, which hides them from enzymes and the kidneys. CJC-1295 with DAC uses a similar trick, which is why it lasts days instead of minutes.
How long does it take to clear a peptide?
About five half-lives clears roughly 97% of a peptide from the body.
| Peptide | Half-life | About 5 half-lives |
|---|---|---|
| Semaglutide | About 1 week | About 5 weeks |
| Tirzepatide | About 5 days | About 25 days |
| Liraglutide | About 13 hours | About 3 days |
| Tesamorelin | About 26 to 38 minutes | About 2 to 3 hours |
This matters before surgery, pregnancy plans or switching medicines, which is why labels give guidance on stopping. Ask your prescriber rather than relying on these estimates.
Why do weekly injections build up?
When a new dose arrives before the last one is cleared, the levels stack up until they reach a steady state, usually after about four to five half-lives. For semaglutide that takes about 4 to 5 weeks at the same dose.
That is one reason the labels raise doses slowly, every 4 weeks; see the GLP-1 titration schedule.
What about research peptide half-lives online?
Treat them with caution: for most research peptides there is no human pharmacology data, and figures online usually come from animal studies or guesses. A rat half-life doesn’t tell you how long a peptide lasts in a person.
Is half-life the same as shelf life?
No: half-life is how long a peptide lasts in the body, while shelf life is how long a vial stays usable in storage.
A mixed vial’s limit comes from its label or the 28-day multiple-dose rule; see how long reconstituted peptides last.