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 Protocol

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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.

Half-life hours

Dose per injection mcg

mcg

Dosing interval hours between injections

Time span days to plot

Plasma concentration over time

Steady state

—d

Peak (Cmax)

—mcg

Trough (Cmin)

—mcg

Accumulation

—×

Educational model only. This is a simplified first-order single-compartment model. Real pharmacokinetics involves absorption, distribution, metabolism, and excretion that depend on the specific peptide, route, and individual physiology. Do not use this output for clinical decisions.

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.

Per-peptide pharmacokinetics

Pre-loaded half-life and cadence for each peptide that has confident PK data — open one to see steady-state, accumulation factor, and peak/trough already plotted.

AOD-9604 2h

~2h half-life. Daily dosing is pulsed rather than steady-state.

BPC-157 4h

Estimated ~4h subq half-life. Many users split into 2× daily doses to maintain tissue exposure.

Cagrilintide 7.5d

Long-acting amylin analog; ~180h half-life supports weekly dosing, often paired with semaglutide.

CJC-1295 8d

DAC-linked form: half-life ~8 days. Every-other-day dosing creates steady baseline elevation of GHRH signal.

Epithalon 30min

Very short plasma half-life; cycles are typically 10–20 days once or twice per year.

GHK-Cu 2h

~2h plasma half-life. Topical and subcutaneous routes both used; collagen effects take weeks to show.

GHRP-2 15min

15 min half-life. Multi-dose daily protocols (pre-meal) aim to mimic ghrelin pulses.

GHRP-6 30min

~30 min half-life; typically dosed 2–3× per day including pre-bed.

HCG 33h

Plasma half-life of ~33h supports every-other-day or twice-weekly microdosing for HPG support.

Hexarelin 1h

~1h half-life. Tachyphylaxis is common; short courses are typical.

HGH (Somatropin) 2.5h

Native rhGH cleared in a few hours. Daily injection produces one "pulse" rather than physiological pulsatility.

HGH Fragment 176-191 2h

Same molecule family as AOD-9604; short half-life, pulse-style dosing.

IGF-1 LR3 25h

LR3 modification extends half-life to ~20–30h. Daily dosing leads to moderate accumulation (~2×).

Ipamorelin 2h

Selective GHRP with ~2h half-life. Typically dosed before bed to ride natural nocturnal GH pulse.

KPV 2h

~2h plasma half-life; anti-inflammatory effects persist beyond plasma clearance.

Liraglutide 13h

Short half-life (~13h) is why liraglutide requires daily injection, unlike its weekly successors.

LL-37 2h

~2h plasma half-life; daily dosing during active protocol.

Mechano Growth Factor 30min

Very short half-life; used as site-injection post-training rather than for steady plasma levels.

Melanotan II 34h

~33h half-life produces meaningful accumulation; loading phase stops once desired pigmentation is reached.

MOD-GRF (1-29) 30min

Without DAC: ~30 min half-life. Preserves pulsatility; usually dosed pre-bed.

MOTS-c 2h

Mitochondrial peptide with short plasma half-life; protocols commonly dose 3× per week.

PT-141 2h

~2h half-life. Used acutely (pre-event) rather than for steady-state pharmacology.

Retatrutide 6d

Half-life of ~6 days; weekly cadence in phase 2 trials produced steady-state in ~4 weeks.

Semaglutide 7d

Half-life of ~7 days drives once-weekly dosing; steady state reached at 4–5 weeks.

Sermorelin 12min

10–15 min half-life. Each evening injection produces a brief GHRH pulse; no accumulation between doses.

Survodutide 7d

Dual GLP-1/glucagon agonist; weekly dosing, steady state takes ~5 weeks.

TB-500 5h

Thymosin-β4 fragment has short plasma half-life but binds actin systemically; weekly or twice-weekly cadence typical.

Tesamorelin 30min

Very short half-life but daily dosing generates repeated GHRH pulses; plasma mass is cleared quickly between doses.

Thymosin Alpha-1 2h

~2h plasma half-life. Clinical dosing is 2× weekly — the immune effect outlasts plasma clearance.

Tirzepatide 5d

Half-life of ~5 days; weekly dosing allows steady accumulation with moderate peak-to-trough variation.

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.

See your real protocol, not just the math

Peptide Protocol logs every actual injection time and shows you a real timeline — not a model. Adjust dosing based on what your body is doing, not what the spreadsheet says.

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Disclaimer. This tool is provided for educational purposes only. The model is a simplified first-order single-compartment exponential decay and does not represent any individual's actual pharmacokinetics. Always consult a qualified healthcare provider before beginning any peptide protocol.