Guide
Understanding peptide half-lives
Half-life is the single most useful number for choosing a research administration interval. It determines accumulation, time to steady state, and the gap between peak and trough.
The half-life definition
A peptide's half-life (t½) is the time required for plasma concentration to fall by half. Half-life is a property of the peptide, not the dose: doubling the dose doubles the peak, but the time to halve that peak is unchanged.
Steady state and accumulation
Repeated dosing produces an exponential approach to a stable average plasma concentration — the steady state. Practically, steady state is reached after about five half-lives. The accumulation factor at a chosen interval τ is 1 ÷ (1 − e−kτ), where k = ln(2) ÷ t½.
Two examples:
- Semaglutide (t½ ≈ 168 h) dosed weekly accumulates by a factor of ≈ 2.0 and reaches steady state in ~35 days.
- Tesamorelin (t½ ≈ 0.4 h) administered daily shows no accumulation — each dose acts independently.
How half-life drives interval choice
Short-half-life peptides (GHRH analogs, AOD-9604) are typically dosed daily because the target effect is pulsatile receptor activation, not steady-state coverage. Long-half-life peptides (incretin analogs) are dosed weekly because steady-state coverage is the goal. Healing peptides with intermediate half-lives often sit somewhere in between, with twice- or thrice-weekly schedules common in research literature.
Try the interactive simulator
The Half-Life Calculator renders the concentration curve for any peptide, dose and interval — useful for visualising why collapsing a weekly schedule to twice weekly halves the peak swing.