What is a peptide's half-life?

Half-life is the time it takes for the concentration of a peptide in your blood to drop by 50%. After 5 half-lives, roughly 97% of a single dose has been cleared.

How is steady state calculated?

Steady state — where average plasma concentration becomes stable across doses — is reached after approximately 4 to 5 half-lives of consistent dosing. Until then, each dose adds to a rising baseline.

Why does dosing frequency matter?

Short-half-life peptides (like Sermorelin or GHRP-2 at ~15 minutes) clear before the next dose if injected too infrequently — concentration spikes and drops. Long-half-life peptides (like Semaglutide at ~7 days) accumulate steadily and only need weekly dosing.

Is this a clinical pharmacokinetic model?

No. This visualizer uses simple first-order exponential decay (C = D × e^(−ln(2) × t / t½)) for educational illustration. Real pharmacokinetics involves absorption rates, two-compartment models, protein binding, and individual metabolism — none of which are modeled here.

Why do some peptides have half-lives in minutes and others in days?

Native peptides like GnRH or DSIP are rapidly degraded by enzymes — half-lives of minutes. Modified peptides like Semaglutide, CJC-1295 with DAC, or IGF-1 LR3 carry chemical modifications (fatty-acid chains, DAC linker, amino-acid substitutions) that shield them from enzymes, extending half-life into days.

Peptide Half-Life Visualizer

See exactly how a peptide's blood concentration rises, falls, and reaches steady state given its half-life and your dosing frequency. Pick a preset or enter custom values.

How half-life shapes a protocol

Half-life (t½) is the time it takes for plasma concentration of a peptide to fall by 50%. It's the single most important pharmacokinetic property because it controls:

How often you need to dose. If you inject more frequently than ~1 half-life, you accumulate. Less frequently, you get peaks and troughs.
How long until steady state. Steady state — the point where average concentration stops rising — is reached after ~4–5 × t½ of consistent dosing.
How long after a dose effects persist. After 5 half-lives, ~97% of a single dose is cleared.

The math

This visualizer uses simple first-order exponential decay:

C(t) = D × e^(−ln(2) × t / t½)

Where D is the dose, t is time since injection, and t½ is the half-life. For repeat dosing, each injection adds a new decaying curve to the existing total.

Steady state and accumulation

For a peptide with half-life t½ dosed every τ hours, the accumulation factor is:

R = 1 / (1 − 0.5^(τ/t½))

If you dose at exactly the half-life (τ = t½), R = 2 — steady-state peak is twice your single dose. If you dose at 2 × t½, accumulation is much smaller (R ≈ 1.33).

Short vs long half-life peptides

Minutes — Sermorelin, GnRH, GHRP-2, GHRP-6. Designed to mimic natural pulses; injected and gone within an hour.
Hours — BPC-157, TB-500, Ipamorelin. Daily or twice-daily dosing typical.
Days — CJC-1295 with DAC, MOTS-c, Tesamorelin, Melanotan II. Twice-weekly to weekly dosing.
Week+ — Semaglutide (~7 days), Tirzepatide (~5 days), Retatrutide (~6 days). Once-weekly clinical dosing; steady state takes ~4–6 weeks.

Frequently asked

How many half-lives until steady state?

Approximately 4–5 half-lives. For Semaglutide (~7 days), steady state takes ~4–5 weeks of consistent weekly dosing. This is why dose escalation protocols wait several weeks between increases — you're titrating against a still-rising baseline.

Why do peaks shrink toward steady state?

They don't — they grow. As prior doses accumulate, each new dose lands on a higher baseline, so peaks rise. What stabilizes is the difference between peak and trough across each dosing interval.

What if I dose more frequently than the half-life?

You'll accumulate substantially. If you dose at τ = t½/2, accumulation factor is ~3.4×. This is why short-half-life peptides like GHRPs are dosed multiple times per day — the goal is mimicking pulses, not maintaining steady levels.

Is plasma concentration the same as effect?

No. Some peptides have effects long after they've cleared (TB-500 binds and modifies cellular state). Others act only when bound to receptors at meaningful concentrations. This chart shows mass in plasma — useful for dosing math, but not a direct picture of biological effect.

Where do half-life values come from?

Published pharmacokinetic studies, manufacturer prescribing information (where applicable), and peer-reviewed literature. Many research peptides have only animal-model PK data, so values are estimates. Use the values printed on your specific product when available.

Peptide half-life visualizer