A peptide's half-life is the time it takes for half of the administered dose to be cleared from your body. This single number determines how often you need to inject, whether you should split doses, and how long effects last after each administration. Getting your timing wrong can mean the difference between stable peptide levels and a roller coaster of peaks and troughs.
Peptide Half-Life Reference Chart
| Peptide | Approximate Half-Life | Recommended Dosing Frequency | Notes |
|---|---|---|---|
| BPC-157 | 4 hours | 1-2x daily | Stable; split dosing provides more consistent levels |
| TB-500 | 8-12 hours | 2x weekly | Long-acting; systemic distribution |
| Ipamorelin | 2 hours | 2-3x daily | Short-acting GH secretagogue; fasting required |
| CJC-1295 (no DAC) | 30 minutes | 2-3x daily (with GHRP) | Very short; always paired with a GHRP |
| CJC-1295 (with DAC) | 6-8 days | 1-2x weekly | Long-acting due to albumin binding |
| Semaglutide | ~7 days | Once weekly | Albumin binding extends duration dramatically |
| Tirzepatide | ~5 days | Once weekly | Dual GIP/GLP-1 agonist |
| AOD-9604 | ~30 minutes | Once daily (fasted) | Very short; effects outlast plasma levels |
| GHK-Cu | ~4 hours | Once daily | Effects are cumulative over weeks |
| Semax | ~1 hour (intranasal) | 1-2x daily | Short but rapid onset; effects last 4-6 hours |
| Selank | ~1-2 hours (intranasal) | 1-2x daily | Similar profile to Semax |
| PT-141 | ~2 hours | As needed (max 1x per 24hrs) | Effects last 24-72 hours despite short half-life |
| Thymosin Alpha-1 | ~2 hours | 2-3x weekly | Immune effects persist beyond plasma clearance |
| DSIP | ~7 minutes (IV) | Nightly | Very short plasma half-life; neurological effects longer |
| IGF-1 LR3 | 20-30 hours | Once daily | Modified for extended half-life |
| MGF | ~5-7 minutes | Post-workout only | Extremely short; PEGylated version lasts longer |
What Half-Life Means for Your Protocol
Short Half-Life Peptides (under 2 hours)
Peptides like CJC-1295 (no DAC), Semax, and DSIP clear the body rapidly. This means:
- Multiple daily doses may be needed for consistent levels
- Timing relative to meals, sleep, or exercise matters more
- Miss a dose and levels drop quickly
Medium Half-Life Peptides (2-12 hours)
BPC-157, Ipamorelin, and TB-500 fall in this range. They offer:
- More flexibility in dosing schedules
- Once or twice daily dosing is usually sufficient
- Missing a single dose is less impactful
Long Half-Life Peptides (days to weeks)
CJC-1295 with DAC and semaglutide have extended half-lives due to albumin binding. Benefits include:
- Once-weekly dosing convenience
- Very stable blood levels with minimal fluctuation
- Effects persist for days after each dose
Half-Life vs Duration of Effect
An important distinction: half-life is not the same as duration of effect. Many peptides trigger biological cascades that persist long after the peptide itself has been cleared. For example:
- PT-141 has a 2-hour half-life but effects can last 24-72 hours because it activates melanocortin receptors that continue signaling.
- Thymosin Alpha-1 clears in hours but its immune-modulating effects last days because it stimulates T-cell maturation — a process that continues independently.
- GH secretagogues (Ipamorelin, GHRP-6) have short half-lives but the GH pulse they trigger lasts 2-3 hours and the downstream IGF-1 elevation lasts even longer.
Practical Timing Tips
- GH secretagogues: Always inject fasted (2+ hours after eating). Food blunts the GH response. Best times: morning (fasted) and before bed (fasted 2+ hours).
- BPC-157: Split into two daily doses for more consistent levels. Morning and evening work well.
- Semaglutide/Tirzepatide: Pick a consistent day each week. Same day, same general time.
- Semax/Selank: Dose in the morning for daytime cognitive effects. Avoid evening Semax as it may interfere with sleep.
Does injection site affect half-life?
Minimally for subcutaneous injections. SubQ injection creates a depot that absorbs gradually, which can slightly extend the effective half-life compared to IV administration. Intramuscular injection may absorb slightly faster due to greater blood flow in muscle tissue.
If a peptide has a short half-life, does that mean it doesnt work well?
Not at all. Half-life is about clearance, not effectiveness. Many highly effective peptides have very short half-lives but trigger biological effects that last much longer. The key is dosing at the right frequency to maintain the biological response you want.