The growth-hormone axis

The growth-hormone axis is the endocrine spine that connects pituitary somatotroph cells, hepatic IGF-1 production, and downstream tissue effects on muscle, bone, fat distribution, and metabolic substrate handling. Four peptides on this site interface with that axis through three distinct receptor pathways: Tesamorelin and CJC-1295 act on the GHRH receptor, Ipamorelin acts on the ghrelin receptor (GHSR-1a), and MK-677 — technically a non-peptide spiropiperidine, included here as peptide-adjacent — also acts on GHSR-1a but is orally bioavailable.

This dossier surveys what each pathway does mechanistically, what the human evidence base actually supports for each compound, where the practitioner protocols sit relative to the trial-grade evidence, and what is genuinely unknown about chronic GH-axis modulation in healthy adults.

The compounds split cleanly along two dimensions: receptor (GHRH versus ghrelin) and temporal pattern (pulsatile versus tonic). GHRH receptor agonism preserves the pulsatile, feedback-regulated character of native GHRH-driven GH release; ghrelin receptor agonism does the same but through a parallel pathway that engages somatotrophs differently. The DAC modification on CJC-1295 produces tonic rather than pulsatile stimulation, which is why CJC-1295 with DAC carries a different risk profile than its non-DAC counterpart and a different one again from Ipamorelin.

The practical clinical question in every case is the same: at therapeutic doses for an indication that mechanistically maps onto the molecule's pharmacology, what does sustained GH-axis activation produce — and what does it produce that the published evidence base does not yet adequately characterize?