Peptide Half-Life Comparison Chart

What Is Elimination Half-Life?

The elimination half-life (t½) of a drug is the time it takes for the plasma concentration to decrease by half after distribution equilibrium is reached. It is one of the most important pharmacokinetic parameters because it determines how frequently a drug needs to be administered and how long it takes to reach steady state or to wash out of the system.

Among research peptides, half-lives vary enormously — from minutes (kisspeptin-10, oxytocin, GnRH) to days (semaglutide, cagrilintide, CJC-1295 DAC). This wide range reflects differences in molecular size, protein binding, albumin conjugation, and resistance to enzymatic degradation.

Half-Life and Dosing Frequency

As a general rule, drugs are dosed at intervals equal to or slightly less than their half-life to maintain therapeutic plasma levels. This is why:

• Semaglutide (t½ ~7 days) is dosed once weekly
• Liraglutide (t½ ~13 hours) is dosed once daily
• BPC-157 (t½ ~4 hours estimated) is typically dosed 1–2 times daily
• Ipamorelin (t½ ~2 hours) is typically dosed 2–3 times daily
• Sermorelin (t½ ~12 minutes) requires frequent dosing or sustained-release formulations

Time to Steady State

With repeated dosing at regular intervals, a drug accumulates until the amount eliminated per dosing interval equals the amount administered. This equilibrium (steady state) is reached after approximately 4–5 half-lives, regardless of the dose or frequency.

For semaglutide (t½ ~7 days), steady state takes about 4–5 weeks. For tirzepatide (t½ ~5 days), it takes about 3–4 weeks. For short-acting peptides like ipamorelin (t½ ~2 hours), steady state is reached within hours of starting a regular dosing schedule.

Washout Period

The washout period is the time required for a drug to be essentially eliminated from the body after the last dose. After 5 half-lives, approximately 97% of the drug has been eliminated. This is important for:

• Planning drug holidays or cycling protocols
• Understanding how long side effects may persist after discontinuation
• Timing switches between different medications
• Interpreting drug testing results

Why Some Peptides Have Long Half-Lives

Most natural peptides are rapidly degraded by proteases and have half-lives measured in minutes. Modern pharmaceutical engineering has developed several strategies to extend peptide half-lives:

• Fatty acid conjugation (semaglutide, liraglutide): A fatty acid chain enables reversible binding to serum albumin, protecting the peptide from degradation and slowing renal clearance.
• Drug affinity complex (DAC) (CJC-1295 DAC): A reactive chemical moiety covalently bonds to albumin in the body.
• Fc fusion (some investigational peptides): Fusing the peptide to an antibody Fc fragment extends half-life via the neonatal Fc receptor (FcRn) recycling pathway.
• Amino acid modifications (many peptides): Substituting D-amino acids, N-methylation, or cyclization resists protease digestion.

Evidence Levels for Half-Life Data

The reliability of half-life values varies significantly across peptides:

• Clinical (green dot): Derived from formal pharmacokinetic studies in humans. Examples include FDA-approved drugs with extensive PK characterization.
• Preclinical (yellow dot): Based on animal pharmacokinetic studies. Values may differ in humans due to species-specific metabolism and protein binding.
• Estimated (gray dot): Approximate values inferred from dosing recommendations, limited data, or extrapolation. Should be interpreted with caution.

References

• Lau J, et al. Discovery of the once-weekly GLP-1 analog semaglutide. J Med Chem. 2015;58(18):7370-7380. PMID: 26308095
• Overgaard RV, et al. Clinical PK of oral semaglutide. Clin Pharmacokinet. 2021;60(10):1335-1348. PMID: 33969456
• Jastreboff AM, et al. Tirzepatide once weekly for obesity. N Engl J Med. 2022;387(3):205-216. PMID: 35658024
• Teichert M, et al. CJC-1295, a long-acting GHRH analog. J Clin Endocrinol Metab. 2006;91(3):799-805. PMID: 16352683
• FDA 2005 Guidance for Industry: Estimating the Maximum Safe Starting Dose in Initial Clinical Trials.