May 16, 2026
Peptide Half-Life Explained: Why It Matters for Your Dosing Schedule
Half-life determines how long a compound stays active in your body. Understanding it helps you dose smarter and avoid accumulation.
If you have spent any time reading about peptides, you have seen the term "half-life." It sounds technical, but the basic concept is simple — and it has real implications for your dosing schedule.
What is half-life?
Half-life (t½) is the time it takes for the concentration of a compound in your blood to drop by 50%. After one half-life, 50% remains. After two, 25%. After three, 12.5%. After about five half-lives, the compound is effectively eliminated from your body.
Why it matters for dosing
Short half-life (≤ 2 hours) — Compounds like GHRP-2, ipamorelin, and sermorelin need multiple daily doses to maintain effect. Dose timing relative to meals becomes critical because glucose suppresses GH release.
Medium half-life (2–24 hours) — Liraglutide (13 h) fits here. Once-daily dosing works. Miss a dose and you feel it the next day.
Long half-life (≥ 100 hours) — Semaglutide (165 h) and tirzepatide (120 h) are once-weekly. Steady state takes 4–5 weeks to reach. Dose changes take weeks to show full effect — and side effects can linger.
Steady state
With repeated dosing at regular intervals, the drug concentration builds up until it reaches a plateau called steady state. For once-weekly GLP-1s, this happens around week 4–5. That means the full glycaemic and weight-loss benefit may not appear immediately — patience is required.
Practical takeaways
- Map your dosing schedule to the compound's half-life — not the other way around.
- When switching doses, allow 5 half-lives to reach a new steady state before judging efficacy.
- Track consistently. A 7-day log won't tell you much about a compound with a 7-day half-life; you need 4–8 weeks of data.
TrackPep calculates half-life-based scheduling automatically when you log a compound, and it shows your estimated blood concentration over time.