1. What half-life means
The half-life of a compound is the time it takes for its concentration in the body to reduce by half. After one half-life, 50% remains. After two, 25%. After five half-lives, less than 4% remains — effectively cleared.
Example: 30-minute half-life
T+0 min: 100% of dose present
T+30 min: 50% remaining
T+60 min: 25% remaining
T+90 min: 12.5% remaining
T+120 min: 6.25% remaining
T+150 min: ~3% remaining — effectively cleared
Note: half-life describes concentration decline, not effect duration. A compound can produce lasting biological changes even after it's been cleared (e.g., BPC-157 healing effects persist after the peptide clears).
2. How half-life determines dosing frequency
To maintain a relatively steady state of a compound in your system, you need to redose before the previous dose has fully cleared. As a rough rule:
| Half-life range | Typical dosing frequency |
|---|---|
| < 1 hour | 2–3x daily for sustained effect; once daily for pulsed dosing |
| 1–4 hours | Once to twice daily |
| 4–12 hours | Once daily |
| 12–24 hours | Once daily to every other day |
| 1–3 days | Every 2–3 days |
| ~7 days | Once weekly |
3. Half-life reference table
| Peptide | Half-life | Typical dosing |
|---|---|---|
| BPC-157 | ~4 hours (estimated) | Once or twice daily sub-Q |
| TB-500 | Days (estimated) | 2x/week or weekly |
| CJC-1295 No-DAC (Modified GRF) | ~30 minutes | 1–3x daily (pulsed) |
| CJC-1295 with DAC | ~7 days | Once or twice weekly |
| Ipamorelin | ~2 hours | 1–3x daily |
| GHRP-2 | ~1 hour | 2–3x daily |
| GHRP-6 | ~1 hour | 2–3x daily |
| Sermorelin | ~10 minutes | 1–2x daily (pre-bed) |
| Semaglutide | ~7 days | Once weekly |
| Tirzepatide | ~5 days | Once weekly |
| Retatrutide | ~6 days | Once weekly |
| PT-141 | ~2 hours | As needed (not daily) |
| Semax | ~30–60 minutes | 1–2x daily (intranasal or sub-Q) |
| Selank | ~30–60 minutes | 1–2x daily |
| Epithalon | ~30 minutes | Once daily during cycle |
| GHK-Cu | ~30 minutes | Once daily or topical |
Half-life estimates for research peptides are often derived from animal data or extrapolated from limited human pharmacokinetic studies. Individual variation and route of administration affect actual clearance.
4. Half-life and detection times
Detection window is not the same as half-life. A compound may be undetectable within hours in blood but remain detectable in urine for much longer. Relevant for competitive athletes subject to WADA testing:
- Most short-half-life peptides (CJC No-DAC, ipamorelin, BPC-157) have urine detection windows of 24–72 hours with current methods.
- Long-acting peptides (CJC with DAC, semaglutide) may be detectable for 1–4 weeks.
- WADA detection methods for peptides are improving rapidly — historical estimates become unreliable quickly.
- If anti-doping compliance is relevant to you, consult the most current WADA prohibited list and testing guidelines rather than forum estimates.