Growth Hormone Secretagogues — GHRH & GHRP Research Guide

What Are Growth Hormone Secretagogues?

A growth hormone secretagogue (GHS) is any compound that prompts the body to release its own growth hormone (GH) from the pituitary gland, rather than supplying GH from outside. This is the defining distinction researchers care about: a secretagogue works upstream, stimulating endogenous secretion through the body’s native signalling pathways, so the resulting GH pulse still passes through normal feedback control. The peptides in this class are among the most widely studied research chemicals in the growth-hormone axis, and OL Research stocks several of them.

This overview explains the two mechanistic families of GH secretagogue, why they are so often combined, and how the individual compounds — Ipamorelin, CJC-1295 and Tesamorelin — differ. It is written for laboratory research use only.

The GH Axis in Brief

Pituitary GH release is governed by two opposing hypothalamic signals: growth-hormone-releasing hormone (GHRH), which stimulates release, and somatostatin, which suppresses it. A third input, the stomach-derived hormone ghrelin, acts through the growth-hormone secretagogue receptor (GHS-R) to amplify release. GH is not secreted continuously — it is released in pulses, and that pulsatility is biologically important. Because secretagogues drive the pituitary through these native channels, they tend to preserve the natural pulsatile pattern and the feedback loops that limit it — the property most often contrasted with exogenous recombinant GH in the literature.

The Two Classes of Secretagogue

1. GHRH Analogues

These mimic the body’s own GHRH, binding the GHRH receptor on the pituitary to stimulate GH synthesis and release. Native GHRH is degraded within minutes, so research analogues are engineered for stability:

Sermorelin — GHRH(1–29), the shortest fully active fragment; short-acting.
CJC-1295 — a stabilised GHRH analogue. The “DAC” (Drug Affinity Complex) version binds albumin to extend its half-life to days; the “no-DAC” version (also called Mod-GRF 1-29) is short-acting. The difference is significant enough to warrant its own guide: see CJC-1295 DAC vs No-DAC.
Tesamorelin — a stabilised GHRH analogue with the strongest evidence base of the group, studied specifically for its effect on visceral adipose tissue.

2. GHRPs and Ghrelin Mimetics

These act on the GHS-R (the ghrelin receptor), the same target the stomach’s ghrelin uses. They stimulate GH release through a pathway that is complementary to GHRH and also blunts somatostatin’s braking effect:

Ipamorelin — the most selective GHRP studied. It triggers GH release with little to no effect on cortisol, prolactin or appetite, which is why it is the reference compound for a “clean” secretagogue signal.
GHRP-2 and GHRP-6 — earlier, more potent GHRPs, but less selective; GHRP-6 in particular strongly stimulates hunger, and both can raise cortisol and prolactin at higher doses.
Hexarelin — highly potent but prone to receptor desensitisation in research models.
MK-677 (Ibutamoren) — an orally active, non-peptide ghrelin mimetic with a long half-life, notable for being investigated as a once-daily oral secretagogue rather than an injectable.

Why GHRH and GHRP Are Studied Together

The single most important concept in secretagogue research is synergy. A GHRH analogue and a GHRP act on two different receptors through two different mechanisms — one pushing the accelerator (GHRH), the other both pushing the accelerator and easing the brake (GHRP suppressing somatostatin). Combined, they produce a GH pulse substantially larger than the sum of either alone. This is why the CJC-1295 + Ipamorelin pairing is the canonical research combination: a stabilised GHRH analogue plus the cleanest GHRP, timed to co-stimulate a single amplified, still-pulsatile release. The CJC-1295 & Ipamorelin research page covers this pairing in depth.

Secretagogues vs Exogenous GH

Researchers distinguish secretagogues from recombinant human GH (rhGH) on three points that recur throughout the literature:

Pulsatility — secretagogues evoke a pulse and then let levels fall, echoing natural secretion; rhGH produces a sustained, non-physiological elevation.
Feedback intact — because release still passes through somatostatin and IGF-1 negative feedback, the system retains a ceiling; exogenous GH bypasses this entirely.
Upstream site of action — secretagogues depend on a functioning pituitary, which is itself a variable researchers study.

Comparison of the Main Secretagogues

Ipamorelin	GHRP / ghrelin mimetic. Most selective — minimal cortisol, prolactin or appetite effect. The “clean” reference GHRP. See the Ipamorelin guide · Ipamorelin 10mg.
CJC-1295	GHRH analogue. DAC version is long-acting (albumin-bound, days); no-DAC is short-acting. Usually paired with a GHRP. See DAC vs No-DAC · DAC 5mg · No-DAC 10mg.
Tesamorelin	GHRH analogue with the strongest evidence base; studied for visceral adipose tissue specifically. See the Tesamorelin guide · Tesamorelin 10mg.
GHRP-2 / GHRP-6	Potent GHRPs but less selective; GHRP-6 strongly stimulates appetite, both can raise cortisol/prolactin.
MK-677 (Ibutamoren)	Orally active, long-acting ghrelin mimetic — studied as a once-daily oral secretagogue.

The simplest framing: GHRH analogues (CJC-1295, Tesamorelin, Sermorelin) supply the “release” signal; GHRPs (Ipamorelin and relatives) amplify it and release the brake — and the two classes are most informative when studied together. Note that the hGH fragment AOD9604 is not a secretagogue — it is a GH-derived fragment studied for a separate, non-GH-releasing mechanism.

Experimental Considerations

All the peptide secretagogues are supplied as lyophilised (freeze-dried) powder for reconstitution and are not orally stable (MK-677 being the non-peptide exception). Data quality depends heavily on handling:

Reconstitution — prepare with bacteriostatic water using standard technique; see the Peptide Reconstitution Guide for concentration and volume calculations.
Timing — because the GHRH+GHRP synergy depends on co-stimulation, protocols pay close attention to the interval between compounds and to somatostatin tone at the time of the pulse.
Storage — keep lyophilised vials cold and dark; reconstituted solution is short-lived and should be refrigerated. See Peptide Storage best practices.
Purity — OLR secretagogues are supplied at ≥99% HPLC purity, UK-dispatched. Purity and correct reconstitution are the two biggest determinants of reproducible results.

Frequently Asked Questions

What is a growth hormone secretagogue?
A compound that stimulates the body to release its own growth hormone from the pituitary, rather than supplying growth hormone from outside. It acts upstream, through the GHRH or ghrelin (GHS-R) pathways.

What is the difference between a GHRH analogue and a GHRP?
A GHRH analogue (e.g. CJC-1295, Tesamorelin) mimics growth-hormone-releasing hormone and directly stimulates release. A GHRP (e.g. Ipamorelin) acts on the ghrelin receptor to amplify release and suppress somatostatin’s inhibitory signal. They work through different receptors, which is why they are synergistic.

Why are CJC-1295 and Ipamorelin used together in research?
They stimulate GH release through two complementary mechanisms, producing a combined pulse larger than either alone while preserving the natural pulsatile pattern. See the CJC-1295 & Ipamorelin research page.

How do secretagogues differ from injectable growth hormone?
Secretagogues evoke a natural, pulsatile release that remains subject to the body’s negative feedback; exogenous recombinant GH produces a sustained, non-physiological elevation that bypasses that feedback.

What are these compounds used for?
In the UK they are supplied strictly as laboratory research chemicals for in-vitro and preclinical study. They are not for human or veterinary use.

Growth Hormone Secretagogues — GHRH Analogues, GHRPs and GH-Axis Research