Introduction
Peptide half-life is a fundamental pharmacokinetic parameter that describes how quickly a compound is cleared from circulation after administration. In research contexts, half-life influences dosing frequency, study design, and interpretation of time-course data. This guide covers the half-lives of the most commonly studied research peptides and explains why these values matter for research protocol design.
What Is Half-Life?
Half-life (t½) refers to the time required for the concentration of a compound in the body to reduce to half its initial value. It is a function of the compound’s distribution volume and clearance rate. For peptides, half-life is largely determined by susceptibility to proteolytic degradation by peptidases in the blood, tissues, and kidneys, as well as renal clearance for smaller peptides.
GHRPs: Short Half-Lives
Growth hormone-releasing peptides are generally short-acting. GHRP-6 has a half-life of approximately 15 to 60 minutes. GHRP-2 is similar, around 30 minutes. Ipamorelin has a half-life of approximately 2 hours. Hexarelin is in the range of 60 to 90 minutes. These short half-lives mean GH pulses produced by these compounds are transient, mimicking natural pulsatile GH release patterns.
GHRHs: Variable Half-Lives
Native GHRH(1-44) has a very short half-life of approximately 7 minutes. Modified versions are substantially more stable. CJC-1295 without DAC (Mod GRF 1-29) has a half-life of approximately 30 minutes due to amino acid substitutions protecting key cleavage sites. CJC-1295 with DAC extends half-life to 6 to 8 days through albumin binding. Sermorelin has a half-life of approximately 10 to 20 minutes.
Repair Peptides
BPC-157 has a half-life estimated at approximately 4 hours in rodent studies, though this varies by administration route. TB-500 (Thymosin Beta-4) has a longer estimated half-life, with systemic effects persisting for days in animal studies due to its albumin-binding properties. IGF-1 LR3 has a half-life of approximately 20 to 30 hours compared to native IGF-1’s half-life of minutes.
Metabolic Peptides
Native GLP-1 has a very short half-life of approximately 2 minutes due to rapid DPP-IV enzyme cleavage. Semaglutide extends this to approximately 7 days through fatty acid modification enabling albumin binding. Tirzepatide has a half-life of approximately 5 days. These extended half-lives are what enable once-weekly dosing in clinical applications.
Neuropeptides
Selank has a moderate half-life of several hours, enhanced from native tuftsin by its Pro-Gly-Pro extension. Semax has a similarly improved half-life over the native ACTH fragment. Epithalon is a small stable tetrapeptide with a relatively prolonged biological effect despite its small size.
Why Half-Life Matters for Research Design
Half-life determines dosing intervals in time-course studies, influences peak-to-trough concentration ratios, affects how long post-administration windows remain relevant for measurement, and must be considered when designing washout periods between treatment conditions.
Conclusion
Research peptide half-lives span from minutes (native GLP-1) to days (CJC-1295 with DAC, Semaglutide). Understanding the half-life of each compound in a research protocol is essential for designing appropriate dosing schedules, measurement windows, and washout periods that produce interpretable, reproducible data.