Growth Hormone Secretagogues: Pulsatile GH, Body Composition, and the GHRH/GHRP Axis

The GHRH receptor lives on the somatotroph cells of the anterior pituitary and responds to natural GHRH (44-amino-acid endogenous peptide) and engineered analogs. Sermorelin (the truncated 1–29 fragment) and Mod GRF 1-29 / CJC-1295 (a Mod GRF 1-29 with or without the DAC bonding extension that prolongs half-life) all bind here. They reset GH amplitude during the body's own natural pulses — they do not create new pulses, they make the existing ones bigger.

The GHS-R1a (ghrelin receptor) is a separate receptor expressed on the same somatotrophs plus hypothalamic feeding centers. GHRPs (Ipamorelin, Hexarelin, GHRP-6, GHRP-2) bind here. They CREATE new GH pulses by mimicking ghrelin — the natural orexigenic hormone that drives GH release alongside the GHRH cycle. Hexarelin and GHRP-6 also have measurable cross-receptor effects (cortisol elevation, prolactin elevation) that the cleaner GHRPs (Ipamorelin) avoid.

The combined protocol exploits both pathways: a GHRH analog raises the baseline pulse amplitude, and a GHRP triggers an additional pulse on top — together they produce a GH peak roughly 2–3× the magnitude of either alone in published research. CJC-1295 (no DAC) + Ipamorelin is the canonical clean stack: short-half-life GHRH analog with the cleanest GHRP, dosed 2–3× daily to mimic natural GH pulse frequency.

The "DAC" suffix on CJC-1295 refers to a Drug Affinity Complex — a small molecular addition that binds the peptide to serum albumin in circulation, extending half-life from ~30 minutes to ~7 days. CJC-1295 DAC produces a continuous, elevated GH "bleed" rather than discrete pulses; CJC-1295 no-DAC (Mod GRF 1-29) produces a sharp pulse that decays within hours and matches the natural GH cycle.

For research protocols studying pulsatile physiology — IGF-1 dynamics, sleep-architecture effects, body-composition recomposition over weeks-to-months — CJC-1295 no-DAC is the appropriate tool. Continuous elevation (CJC-1295 DAC) produces different downstream signaling and is more analogous to recombinant GH than to physiological GH-pulse augmentation.

Tesamorelin sits in a middle position. Its half-life (~30 minutes parent compound, but with sustained IGF-1 effects) and FDA approval for visceral-adipose-tissue research in HIV-associated lipodystrophy give it a unique research profile: studied human clinical data on body-composition endpoints that other secretagogues lack.

The classic CJC-1295 (no DAC) + Ipamorelin protocol: 100 mcg of each, subcutaneously, 2–3× daily — typically morning, post-workout (if applicable), and pre-bed. The pre-bed dose layers onto the natural GH pulse during slow-wave sleep, producing the largest effective pulse of the day. Doses are kept conservative because GH-receptor downregulation is dose-dependent — chasing larger pulses past 100–200 mcg per dose produces diminishing returns and risks tachyphylaxis.

Biomarker tracking: IGF-1 is the canonical GH-axis readout (GH itself is too pulsatile to measure cleanly without 24-hour sampling); fasting glucose for insulin-sensitivity drift; lipid panel + body composition via DEXA at baseline and 12-week endpoints. Published research durations run 8–16 weeks continuous followed by an off period to restore receptor sensitivity.

Co-administration considerations: GH-secretagogue research is incompatible with same-cycle ghrelin-mimetic appetite work (the GHS-R1a receptor is shared); typically separated from any glucocorticoid research because cortisol blunts GH release; and observed to interact with thyroid hormone studies because IGF-1 modulates thyroid binding globulin levels.