Half-Life & Dosing Guide
Why some peptides are injected multiple times a day and others once a week comes down to one number: half-life.
What half-life means here
Half-life is the time it takes for the active concentration of a compound in circulation to drop by half. It determines how quickly levels fall below an effective threshold — and therefore how often dosing must be repeated to maintain a stable level.
Rule of thumb: after 4–5 half-lives, roughly 94–97% of a dose has cleared. Protocols that dose "every half-life" keep levels far more stable than protocols that dose every several half-lives.
Short vs long acting, by class
| Compound class | Approximate half-life context | Typical dosing cadence (research protocols) |
|---|---|---|
| GHRPs (GHRP-2, GHRP-6, Ipamorelin) | Very short (minutes) | 2–3x daily, often with a GHRH analog |
| GHRH analogs (Mod GRF, Sermorelin) | Short (minutes) | 2–3x daily (or 1x nightly in common stacks) |
| hGH / GH peptides context | Hours | Daily or per protocol design |
| GLP-1 class (Semaglutide) | Long (days, albumin binding) | Once weekly |
| BPC-157, TB-500 | Hours (animal-model data) | Daily (often split dosing) |
| Epitalon, Thymalin-like bioregulators | Hours–days (varies) | Short courses / cycles |
Half-life figures here are research-context approximations from published animal/pharmacokinetic studies — always consult the specific literature for the compound you are working with.
Dosing frequency trade-offs
- Stability: more frequent dosing maintains steadier levels, which is why short-acting secretagogues are dosed multiple times daily.
- Convenience & compliance: fewer injections improve consistency — a weekly injection you actually take beats a 3x daily protocol you skip.
- Injection-site load: every injection is a puncture; daily multi-injection protocols add site fatigue and contamination risk.
- Half-life ≠ effect duration: some compounds' biological effects outlast their measurable half-life (downstream signaling, gene-expression changes), so don't dose purely on PK numbers.
Practical protocol design
- Start from published research protocols for the specific peptide — not from a vendor's suggestion.
- Use the shortest effective dosing window implied by the half-life class.
- Keep a log: dose, time, batch, and any observations.
- Adjust one variable at a time.
See also: Effects Timeline and the Reconstitution Calculator.