Understanding Half-Life for Peptides and GLP-1s
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[Guide · Peptide science]

Understanding half-life

7 min read · Also in the Dose Track app under Learn · Updated

Short answer: Half-life is the time it takes for the amount of a drug in your blood to fall by half. It sets how often a compound is taken, how long it lingers after you stop, and how long it takes to build up to a steady level. Short half-lives mean frequent dosing; long ones, like semaglutide at about a week, mean weekly dosing.

What half-life means

After one half-life, half the drug is left. After two, a quarter. After three, an eighth. The fall is a smooth curve, not a cliff.

How much is left after each half-life
Half-lives passedLeft in the bodyCleared
150%50%
225%75%
312.5%87.5%
46.25%about 94%
53.1%about 97%

So a drug is mostly gone after 4 to 5 half-lives. With a 2-hour half-life that is 8 to 10 hours. With a 1-week half-life it is 4 to 5 weeks. The Ozempic label says semaglutide stays in the blood for about 5 weeks after the last dose.

Half-life is not the same as how long the effect lasts. A peptide that triggers a growth hormone pulse can be gone before the effect of that pulse is.

What makes half-lives differ

  • Enzymes. Many natural peptides are cut up by enzymes within minutes.
  • Changes to the molecule. Adding a part that grabs albumin, a blood protein, slows removal. That is how CJC-1295 with DAC lasts days instead of minutes, and how semaglutide lasts about a week.
  • Route. An injection under the skin is absorbed more slowly than one into a vein.
  • You. Kidney and liver function, body size and other factors change how fast you clear a drug. Published numbers are averages.

Half-lives for common compounds

Research info, not a recommendation. Amounts, schedules and timing in this section come from studies (often in animals) and from how people commonly use these compounds. Most are not FDA-approved doses. Your dose is a decision for you and your prescriber.
Published or commonly quoted half-lives
CompoundHalf-lifeWhere the number comes from
SermorelinAbout 10 minutesFormer drug labels (about 6 to 12 minutes after IV dosing)
CJC-1295 without DAC (Mod GRF 1-29)Short, often quoted at about 30 minutesLittle published human data; treat as an estimate
GHRP-2Short, under an hourLittle published human data; treat as an estimate
IpamorelinAbout 2 hoursStudy in healthy men given IV infusions (Gobburu 1999)
BPC-157Under 30 minutes in rats and dogsAnimal study (He 2022); no published human data
TB-500UnknownNo published human data
CJC-1295 with DAC5.8 to 8.1 daysStudy in healthy adults (Teichman 2006)
Semaglutide (Ozempic, Wegovy)About 1 weekFDA label

See any compound in the half-life calculator to watch levels rise and fall over a schedule.

Short and long half-lives in practice

Short half-life compounds rise and fall within hours. They are taken more often, or timed to a moment. For growth hormone peptides, people often aim at times the body already releases growth hormone, such as soon after falling asleep, when the largest pulse of the day usually happens in early deep sleep.

Long half-life compounds build up over several doses. A missed dose matters less, but it takes longer to reach a steady level. For once-weekly semaglutide, the Ozempic label says steady state is reached after 4 to 5 weeks.

This is why weekly drugs are started at a low dose and raised in steps: each step takes weeks to settle.

Using half-life to plan

  • Clearance: multiply the half-life by 5 for roughly how long until a compound is about 97% gone.
  • Steady state: also about 4 to 5 half-lives of regular dosing. Judge a weekly drug after it has settled, not after the first dose.
  • Two compounds at once: GHRH-type peptides (like CJC-1295) and ghrelin-type peptides (like ipamorelin) act on different receptors, and studies in people show the two kinds together release more growth hormone than either alone. That is the reasoning behind pairing them.

Key points

  • Half-life is the time for the level in your blood to fall by half.
  • After 4 to 5 half-lives a drug is about 94% to 97% gone.
  • Weekly semaglutide reaches a steady level after 4 to 5 weeks, per its label.
  • Half-lives for many research peptides are estimates or come from animals.

See also: Half-life calculator · The Levels chart in Dose Track

This guide is general education, not medical advice. Follow your medicine's label and your prescriber.

Compounds in this guide

SemaglutideCompound guide in the Dose Track library. CJC-1295 with DACCompound guide in the Dose Track library. IpamorelinCompound guide in the Dose Track library. SermorelinCompound guide in the Dose Track library. BPC-157Compound guide in the Dose Track library.
Timing and fasting with peptidesTiming matters most for peptides that release growth hormone. Your body releases growth hormone in pulses,… Stacking basics: combining peptides carefullyStacking means taking two or more compounds at the same time. Some pairs make sense on paper because they… Amino acids, peptides and proteins: what is the difference?Amino acids are single building blocks. Peptides are short chains of them (about 2 to 50). Proteins are…

Frequently asked questions

How long until a drug is out of my system?+
Roughly 4 to 5 half-lives. That clears about 94% to 97% of it. For semaglutide, with a half-life of about a week, that is about 5 weeks.
What is steady state?+
The point where the amount you take in each dose equals the amount your body removes between doses, so levels stop climbing. It takes about 4 to 5 half-lives of regular dosing.
What is the half-life of BPC-157?+
There is no published human data. In rats and dogs it was under 30 minutes (He 2022).

Sources

  1. Ozempic prescribing information and Instructions for Use (Novo Nordisk)
  2. Gobburu JV et al. Pharmacokinetic-pharmacodynamic modeling of ipamorelin in human volunteers. Pharm Res 1999;16(9):1412-6
  3. Teichman SL et al. Prolonged stimulation of GH and IGF-I secretion by CJC-1295 in healthy adults. J Clin Endocrinol Metab 2006;91(3):799-805
  4. He L et al. Pharmacokinetics, distribution, metabolism and excretion of BPC 157 in rats and dogs. Front Pharmacol 2022;13:1026182
  5. Van Cauter E, Plat L, Copinschi G. Interrelations between sleep and the somatotropic axis. Sleep 1998;21(6):553-66
  6. Popovic V et al. GHRP-6-induced GH secretion and the synergic action of GHRP-6 plus GHRH. J Clin Endocrinol Metab 1995;80(3):942-7

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