Understanding Peptide Half-Lives

What Is a Half-Life?

A half-life is the time it takes for the concentration of a substance in your body to decrease by exactly 50%. After one half-life, you have 50% remaining. After two half-lives, 25%. After three, 12.5%. And so on.

This exponential decay follows a predictable pattern:

After about 6-7 half-lives, the peptide is considered to be at negligible levels (less than 1% of the original dose).

Why Half-Life Matters for Dosing

The half-life directly determines:

• How often you need to dose — shorter half-lives need more frequent injections
• Whether levels accumulate — repeated dosing before clearance leads to stacking
• How long effects last — both desired effects and side effects
• Wash-out time — how long until the peptide is fully cleared from your system

Peptide Half-Life Comparison

Peptides span an enormous range of half-lives:

Very Short (minutes)

• DSIP: ~15 minutes
• GHK-Cu: ~30 minutes
• CJC-1295 (no DAC): ~30 minutes

These peptides act quickly but clear rapidly. They often need daily or even multiple daily administrations.

Short (hours)

• AOD-9604: ~1 hour
• BPC-157: ~4 hours
• Ipamorelin: ~2 hours
• Epithalon: ~2 hours

These typically require once or twice daily dosing for sustained effects.

Medium (hours to days)

• TB-500: ~6 hours

In this range, dosing frequency can often be reduced to a few times per week.

Long (days to weeks)

• Tirzepatide: ~5 days (120 hours)
• Retatrutide: ~6 days (144 hours)
• CJC-1295 (with DAC): ~7 days (168 hours)
• Semaglutide: ~7 days (168 hours)

These are the "weekly" peptides. One injection maintains therapeutic levels for days.

The Stacking Effect

When you administer a dose before the previous one has fully cleared, the concentrations add together. This is called "stacking" or "accumulation."

For short half-life peptides dosed frequently, this effect is minimal — each dose is essentially independent. But for longer half-life peptides, stacking is significant and intentional.

Example: Semaglutide has a 7-day half-life. After your first weekly injection of 500 mcg, you still have ~250 mcg circulating when you inject the next dose. The levels continue to build until reaching a steady state, where the amount eliminated each week equals the amount injected.

Use our Half-Life Visualizer to see this stacking effect in action with any peptide.

Pulsatile vs. Sustained Release

For growth hormone secretagogues like Ipamorelin and CJC-1295 (no DAC), the short half-life is actually a feature, not a bug. The pulsatile (burst-then-clear) pattern mimics the body's natural GH release, which comes in pulses throughout the day.

In contrast, CJC-1295 (with DAC) provides sustained elevation — a continuous low level of GH stimulation rather than pulses. Which pattern is better depends on the goals and the individual.

Factors Affecting Individual Half-Life

Published half-life values are averages. Your personal half-life for a given peptide may differ based on:

• Liver function — the liver metabolizes most peptides
• Kidney function — renal clearance is a major elimination pathway
• Body composition — fat-soluble peptides may have extended half-lives in individuals with more body fat
• Age — metabolism generally slows with age
• Hydration status — affects distribution volume
• Injection site — subcutaneous vs. intramuscular vs. intravenous delivery
• Concurrent medications — may compete for metabolic enzymes

Practical Applications

Understanding half-life helps you make better protocol decisions:

• Timing injections — know when to dose for stable levels
• Planning stacks — ensure peptides with different half-lives are timed appropriately
• Managing side effects — know how long to wait for a peptide to clear
• Pre-test washout — know how long before a drug test to stop administration
• Travel planning — schedule doses around trips where you might not have access to refrigeration