GH Secretagogues

Definition

GH Secretagogues are synthetic peptides that stimulate the pituitary gland to release endogenous growth hormone, either by mimicking growth hormone-releasing hormone (GHRH) or by activating the ghrelin receptor (GHSR). This category is mechanistically distinct from Category 6 (direct GH administration): secretagogues preserve the natural pulsatile pattern of GH release, remain subject to somatostatin negative feedback, and therefore carry a more favorable safety profile than exogenous rhGH. They are the most commonly prescribed peptides in functional and longevity medicine practices.

Mechanism of Action

The category divides into two mechanistic subclasses. GHRH analogs (Sermorelin, Tesamorelin, CJC-1295) bind pituitary GHRH receptors to stimulate GH synthesis and release. CJC-1295 with DAC (Drug Affinity Complex) has an extended half-life due to albumin binding. Ghrelin mimetics (Ipamorelin, Hexarelin, MK-677) activate the GHSR-1a receptor — the same receptor targeted by ghrelin, the hunger hormone — producing robust GH pulses. The clinical standard has become combination protocols (e.g., CJC-1295 + Ipamorelin) that activate both receptor pathways simultaneously, producing synergistic GH pulses. MK-677 (Ibutamoren) is technically not a peptide but a non-peptide GHSR agonist; it is included here because it functions identically to ghrelin-mimetic peptides and is universally categorized alongside them clinically.

Regulatory Status

Tesamorelin (Egrifta, Theratechnologies) is FDA-approved for HIV-associated lipodystrophy. Sermorelin was previously FDA-approved for pediatric GH deficiency; the branded form was discontinued but sermorelin remains widely available through 503A compounding pharmacies. CJC-1295, Ipamorelin, and Hexarelin are compounded research peptides — no FDA approval. MK-677 is not approved and exists in a regulatory gray area as an oral compound.

Evidence Base

Tesamorelin has the strongest evidence base — Phase III RCT data from HIV-associated lipodystrophy trials demonstrates visceral fat reduction and IGF-1 normalization. Sermorelin has historical Phase II/III data supporting GH elevation in GH-deficient adults. Ipamorelin has favorable safety data and GH pulse elevation in clinical studies. Long-term mortality-endpoint trials for secretagogues in the aging population are lacking. The clinical rationale — restoring youthful GH pulsatility through a physiologic mechanism — is sound, but translation to hard longevity outcomes in aging adults awaits larger trials.