Growth Hormone Secretagogues (GHS)

Growth hormone secretagogues are compounds that stimulate the anterior pituitary to release endogenous growth hormone (GH). Unlike exogenous GH (recombinant hGH), GHS peptides work through the body's own regulatory mechanisms, producing pulsatile GH release that more closely mimics natural secretion patterns.

Two pathways, one outcome

GH release from the anterior pituitary is controlled by two stimulatory inputs that work synergistically:

1. GHRH pathway

Growth hormone-releasing hormone (GHRH) is a 44-amino-acid hypothalamic peptide that binds GHRH receptors on somatotrope cells. GHRH analogs include:

• Sermorelin — a 29-amino-acid analog of GHRH (the first 29 residues, which retain full biological activity). FDA-approved for diagnostic use and pediatric GH deficiency
• CJC-1295 — modified GHRH analog with extended half-life. Available as CJC-1295 (no DAC) with ~30-minute half-life, or CJC-1295 DAC with ~8-day half-life via albumin binding
• Tesamorelin — GHRH analog FDA-approved for HIV-associated lipodystrophy. The only GHS peptide with current FDA-approved therapeutic indication

2. Ghrelin/GHSR pathway

Ghrelin is a 28-amino-acid peptide (the "hunger hormone") that binds the growth hormone secretagogue receptor (GHSR, also called ghrelin receptor). Synthetic ghrelin mimetics include:

• Ipamorelin — the most selective GHSR agonist. Minimal cortisol or prolactin stimulation
• GHRP-2 — potent GHSR agonist. Also stimulates cortisol, prolactin, and appetite (less selective than ipamorelin)
• GHRP-6 — similar to GHRP-2 with stronger appetite stimulation via ghrelin pathway
• Hexarelin — potent GHSR agonist, possibly the strongest GH-releasing effect but also the most desensitization and cortisol co-stimulation

Synergy: why combinations work

GHRH and ghrelin pathways are synergistic, not additive. Combining a GHRH analog (CJC-1295) with a ghrelin mimetic (ipamorelin) produces a larger GH pulse than either alone because they act on different receptor populations on the same somatotrope cells. The CJC-1295 + ipamorelin combination is the most widely used GHS stack for this reason.

Regulatory feedback

GH release is regulated by a negative feedback loop involving somatostatin, a hypothalamic peptide that inhibits GH release. After a GH pulse (natural or GHS-induced), somatostatin tone increases, limiting subsequent GH release. This is why:

• A second GHS dose within a few hours produces a blunted response
• Optimal GHS timing is spaced >3 hours apart to allow somatostatin tone to decrease
• Bedtime dosing exploits the natural nocturnal reduction in somatostatin tone

GHS vs. exogenous GH

| Parameter | GHS peptides | Exogenous GH (hGH) |

|-----------|-------------|-------------------|

| GH pattern | Pulsatile (physiologic) | Flat/non-pulsatile |

| Negative feedback | Preserved (somatostatin still functions) | Overridden (suppresses endogenous GH) |

| IGF-1 elevation | Moderate, within physiologic range | Dose-dependent, can be supraphysiological |

| Pituitary function | Maintained | Suppressed with long-term use |

| Cost | Lower | Significantly higher |

| FDA approval | Tesamorelin only | Multiple indications |

| Reliability | Depends on intact pituitary function | Direct, dose-predictable |

A critical limitation of GHS peptides: they require functional somatotrope cells. In true pituitary insufficiency, GHS peptides will not produce adequate GH release. This is also why GHS efficacy may decline with age — somatotrope mass and responsiveness decrease.

Safety profile

Common side effects across the class:

• Water retention (sodium reabsorption, dose-dependent)
• Increased hunger (more pronounced with ghrelin-pathway agents)
• Transient numbness or tingling (GH-related)
• Carpal tunnel symptoms at higher GH levels
• Cortisol co-stimulation (GHRP-2, GHRP-6, hexarelin — minimal with ipamorelin)

The safety advantage over exogenous GH is that GHS peptides cannot produce GH levels beyond what the pituitary can naturally secrete — there is a physiological ceiling. Exogenous GH has no such ceiling.