GHRP-2

Older-generation, non-selective ghrelin-receptor agonist that produces a stronger GH pulse than ipamorelin but also raises cortisol and prolactin — the dirty-hormone spillover that ipamorelin was specifically engineered to eliminate. Approved in Japan only for diagnostic GH-deficiency challenge (Pralmorelin, 2007); otherwise gray-market research peptide. For Dylan at 20: SKIP-AT-20. Same "no benefit at peak GH/IGF-1 axis" logic as ipamorelin/CJC-1295, plus an additional reason — if a GHRP ever becomes appropriate (30+ with declining IGF-1), ipamorelin is the obvious cleaner replacement on every dimension that matters.

GHRP-2 (Pralmorelin, KP-102) is a synthetic hexapeptide (D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2) developed in the 1990s by Tulane/Bowers' group and Kaken Pharmaceutical, building on the GHRP-6 scaffold. It was the second-generation GHRP — designed to be more potent at the ghrelin receptor than GHRP-6 while reducing (but not eliminating) the appetite-driving and HPA-axis-spillover effects.

The mechanism in plain English:

1. Ghrelin is the body's "hunger hormone," produced in the stomach. It binds GHS-R1a (growth hormone secretagogue receptor 1a) — a G-protein-coupled receptor on pituitary somatotrophs (GH-producing cells).
2. GHRP-2 mimics ghrelin at GHS-R1a — triggering a discrete pulsatile GH release via the PLC → IP3 → intracellular Ca²⁺ pathway. The downstream pituitary signaling cascade is identical to ipamorelin.
3. The selectivity problem. Unlike ipamorelin (which is engineered to confine activity to GHS-R1a on somatotrophs), GHRP-2 also produces meaningful elevation of:
   • Cortisol/ACTH — via cross-activation of receptors on corticotrophs and CRH-like effects in the hypothalamus. Published challenge studies show cortisol rise of ~30-50% at standard 100 mcg IV diagnostic doses, peaking 30-60 min post-dose.
   • Prolactin — via cross-activation at lactotrophs. Reported rises of ~20-40% at therapeutic doses.
   • Aldosterone — modest, reported in some studies; less consistently characterized.
   • Appetite/ghrelin-axis — GHRP-2 is meaningfully more orexigenic than ipamorelin (drives gut ghrelin signaling; users report noticeable hunger surge especially in fasted state). Less than GHRP-6 but not zero.
4. GH-pulse magnitude is higher than ipamorelin at equivalent doses. Head-to-head pituitary studies report GHRP-2 producing ~20-50% larger peak GH responses than ipamorelin at matched receptor occupancy. This is the historical reason it was preferred in some longevity-clinic and bodybuilding protocols pre-2018 — and the reason it was approved in Japan as a diagnostic challenge agent (you want maximal GH stimulus for the diagnostic test).
5. GHRH synergy (CJC-1295/GHRP-2 stack): Same logic as CJC-1295/ipamorelin. GHRH analogs act at GHRHR (cAMP pathway); GHRP-2 acts at GHS-R1a (PLC/IP3/Ca²⁺ pathway). Co-administration produces larger and more synchronized GH pulses than either alone. The CJC-1295/GHRP-2 combo was one of the dominant gray-market protocols ~2010-2018, before ipamorelin's cleaner profile became widely understood and ipamorelin overtook it as the standard pairing.

Pharmacokinetics (Pihoker et al. 1995, Bowers 1996, Kaken Phase 1 data):

• Half-life ≈ 15-30 minutes (terminal); effective dosing duration ~1-2 hours
• Peak GH response ≈ 15-30 minutes post-SC injection
• Bioavailability: ~5-10% intranasal, ~50-70% subcutaneous, ~90% IV
• Each dose produces one discrete GH pulse lasting ~2 hours
• Plasma clearance essentially complete by ~3 hours

What GHRP-2 is NOT doing:

• Not GHRH-receptor activity (that's CJC-1295/sermorelin/tesamorelin)
• Not direct GH (recombinant GH would be somatropin)
• Not direct IGF-1
• Not selective at GHS-R1a — explicitly distinguished from ipamorelin by HPA/lactotroph spillover
• Not as orexigenic as GHRP-6 — but more than ipamorelin