GH-axis compounds split into two receptor families that work synergistically. Quick decoder for which catalogue compound is which. For the deeper pulsatile-vs-continuous reasoning and the per-compound playbook, see GH Axis Playbook; for the runbook for the standard pre-bed combo, see Pre-Bed GH-Secretagogue Protocol.
The two receptors
| Class | Receptor | What it does |
|---|---|---|
| GHRH analogue | GHRH receptor on pituitary somatotrophs | Asks the pituitary to release stored GH. Subject to somatostatin feedback - physiologic ceiling intact. |
| GHRP / Ghrelin mimetic | GHS-R1a (ghrelin receptor) on the same cells | Activates a parallel signalling pathway, deepens the same pulse. Some GHRPs (GHRP-2, GHRP-6) also raise hunger and cortisol. |
Catalogue compounds - which family?
| Compound | Family | Notes |
|---|---|---|
| Mod GRF 1-29 | GHRH analogue | The standard pulse-preserving GHRH. ~30 min half-life. Pre-bed default. |
| CJC-1295 (DAC) | GHRH analogue (long-acting) | DAC chain extends half-life to days - produces continuous IGF-1 elevation rather than pulses. Different category for risk. |
| Sermorelin | GHRH analogue | The original GHRH(1-29). FDA-approved as Geref. Same architecture as Mod GRF, slightly different pharmacokinetics. |
| Tesamorelin | GHRH analogue | Stabilised GHRH analogue (Egrifta). FDA-approved for HIV lipodystrophy. Visceral-fat indication-specific. |
| Ipamorelin | GHRP / ghrelin mimetic | Selective GHRP - produces GH pulse without raising hunger or cortisol. The clean default GHRP. |
| GHRP-2 | GHRP / ghrelin mimetic | Older GHRP. Stronger pulse than Ipamorelin but raises prolactin and cortisol. Catalogue entry pending. |
| GHRP-6 | GHRP / ghrelin mimetic | Older GHRP with strong appetite-stimulating effect. Useful for bulking; problematic for fat loss. Catalogue entry pending. |
| Hexarelin | GHRP / ghrelin mimetic | Potent older GHRP. Higher desensitisation risk than Ipamorelin. Catalogue entry pending. |
| Somatropin (rHGH) | Neither (recombinant GH itself) | Bypasses the pituitary entirely. Not a secretagogue - direct hormone replacement. |
| MK-677 / Ibutamoren | Oral GHS (small molecule, not peptide) | Continuous GHS-R1a agonist. Same downstream signal as a GHRP, but continuous kinetics rather than pulsed. Different risk frame. |
Synergy logic
GHRH + GHRP combined produces a deeper GH pulse than either alone - they hit different receptors on the same somatotroph cell, and the signalling pathways are additive. Standard pre-bed stack: 100 mcg Mod GRF + 100β200 mcg Ipamorelin SC, 15β30 min before sleep, fasted. See the runbook in Pre-Bed GH-Secretagogue Protocol.
Stack across families, not within
- One GHRH + one GHRP is the ceiling. Stacking two GHRPs (Ipamorelin + GHRP-2 + Hexarelin) saturates the same receptor and accelerates desensitisation; no additional GH benefit. Same logic for two GHRH analogues simultaneously.
- CJC-1295 (DAC) is special. Its long half-life means pairing it with a GHRP shifts the architecture from pulsatile to continuous-elevated. That's a different protocol and a different risk profile from the Mod-GRF + Ipamorelin pre-bed pulse stack.
- Don't stack with rHGH. Exogenous GH suppresses the pituitary directly; secretagogues asking the suppressed pituitary to release GH it isn't making produces nothing. Pick a strategy.
Cross-references
- GH Axis Playbook - the deeper article on which compound for which goal.
- HGH Secretagogue vs Real HGH - the head-to-head decision frame.
- Pre-Bed GH-Secretagogue Protocol - runbook for the standard Mod GRF + Ipamorelin combo.
- Cycling Strategies - when to pulse vs continuous, receptor desensitisation by class.