What Is Half-Life?
A peptide's half-life is the time it takes for the concentration of the peptide in the body to decrease by 50%. After one half-life, 50% of the initial dose remains active. After two half-lives, 25% remains. After five half-lives, less than 3.2% remains — effectively eliminated.
Half-life determines how often you need to inject. Short half-life peptides (e.g., BPC-157 at ~4 hours) require daily or twice-daily dosing. Long half-life peptides (e.g., semaglutide at ~168 hours) need only weekly injections.
The Exponential Decay Formula
Remaining dose = Initial dose × (0.5)^(time elapsed / half-life)
Example: You inject 500 mcg of a peptide with a 6-hour half-life. After 12 hours (2 half-lives), 500 × (0.5)² = 125 mcg remains.
Our Half-Life Visualizer plots this decay curve interactively for any peptide.
Half-Life Reference Chart
| Peptide | Half-Life | Typical Dosing Frequency |
|---|---|---|
| BPC-157 | ~4 hours | 1-2× daily |
| TB-500 | ~2-3 hours | 2× weekly |
| CJC-1295 no DAC | ~30 min | 2-3× daily |
| CJC-1295 + DAC | ~8 days | 1-2× weekly |
| Ipamorelin | ~2 hours | 2-3× daily |
| Semaglutide | ~168 hours | Once weekly |
| Tirzepatide | ~120 hours | Once weekly |
| Retatrutide | ~144 hours | Once weekly |
| GHK-Cu | ~12 min | Topical or 1-2× daily |
| PT-141 | ~2.7 hours | As needed |
| DSIP | ~7 min | Nightly |
| Epitalon | ~30 min | 1× daily (cycled) |
Why Half-Life Matters for Your Protocol
Understanding half-life helps you maintain stable blood levels. For short-half-life peptides, splitting the daily dose into two injections creates a smoother pharmacokinetic profile. For long-half-life peptides, once-weekly dosing maintains consistent therapeutic levels.
Missing a dose has different impacts depending on the half-life. Missing one dose of a weekly peptide has minimal impact. Missing a dose of a twice-daily peptide creates a significant gap in blood levels.
Steady State
After approximately 4-5 half-lives of consistent dosing, a peptide reaches "steady state" — the point where the amount entering the body equals the amount being eliminated. For semaglutide (7-day half-life), steady state is reached after about 4-5 weeks of weekly dosing.