Growth hormone peptides & secretagogues

Q: What is the difference between a GHRH analogue and a GHRP?

They pull the same lever from two sides. A GHRH analogue (sermorelin, CJC-1295, tesamorelin) copies the hormone that tells the pituitary to release GH; a GHRP or ghrelin-receptor agonist (ipamorelin, the GHRP-2/6 family, MK-677) works through the separate ghrelin receptor. Because the two routes add up, they are often combined — see MK-677 vs ipamorelin .

Growth hormone itself, the peptides that make the body release more of it (GHRH analogues and the GHRPs), the oral secretagogue MK-677, and the drugs that suppress GH — grouped by where in the axis they act, and marked approved or experimental.

Two very different groups sit here. Recombinant GH and several analogues are approved prescription medicines; the GHRPs, CJC-1295, MK-677 and sermorelin are sold as unapproved research chemicals. This is a factual map of the axis, not advice or an offer to sell, and nothing here is medical advice.

How the axis works

The pituitary releases growth hormone in pulses, under two opposing controls: GHRH tells it to release, and somatostatin tells it to stop. A third signal, the hormone ghrelin, also drives release through its own receptor. Almost every compound here acts on one of those three points — mimicking GHRH, mimicking ghrelin, adding GH directly, or (in acromegaly) suppressing the whole thing. Most of GH’s growth effect is then carried downstream by IGF-1.

The popular secretagogues, side by side

The three most-searched GH-releasing compounds. Figures come from each entry; a dedicated page works through the injectable-vs-oral choice in full.

	Ipamorelin	CJC-1295 with DAC	MK-677Ibutamoren, Nutrobal
Type	GHRP (injectable)	GHRH analogue (injectable)	Oral secretagogue
Route	subcutaneous (intravenous in study settings)	subcutaneous (intravenous in study settings)	oral (tablet or capsule); oral bioavailability above 60 percent
Dosing	1-3x daily, with at least 3 hours between administrations to limit receptor desensitisation	1-2x per week; because of the half-life of 6-8 days, accumulation occurs over the first weeks	Once daily, usually before sleep
Half-life	~2 hours	~6–8 days (albumin-bound)	~4–6 hours (IGF-1 up 24 h)
Status	In trials	In trials	In trials

Full comparison: MK-677 vs ipamorelin.

The full growth-hormone axis

Every compound in the reference that acts on GH, grouped by where it acts.

Growth hormone itself & long-acting analogues

Recombinant human growth hormone, and the modern once-weekly versions of it.

Somatropin (Genotropin, Norditropin) Approved Recombinant human growth hormone itself: a prescription medicine for growth hormone deficiency.
Somapacitan (Sogroya) Approved Albumin-binding growth hormone analogue injected once weekly instead of daily somatropin.
Somatrogon (Ngenla) Approved Weekly growth hormone fused to three hCG C-terminal peptides, for growth hormone deficiency in children.
Lonapegsomatropin (Skytrofa) Approved Weekly PEG prodrug of growth hormone: the linker cleaves itself and releases unmodified somatropin.

GHRH analogues — the upstream trigger

Copies of the hypothalamic hormone that tells the pituitary to release its own GH.

Sermorelin (Geref) Experimental The active 1-29 fragment of GHRH; once FDA-approved, withdrawn in 2008 for commercial reasons.
Tesamorelin (Egrifta) Approved FDA-approved GHRH analogue that reduces visceral abdominal fat in HIV-associated lipodystrophy.
CJC-1295 with DAC In trials Long-acting GHRH analogue that binds albumin and raises GH release for 6 to 8 days per injection.
Mod GRF 1-29 Experimental Short-acting GHRH analogue: modified sermorelin triggering a single GH pulse without albumin binding.

Ghrelin-receptor agonists (GHRPs & secretagogues)

The other release switch — the ghrelin / GH-secretagogue receptor — including the injectable GHRPs and the oral tablet MK-677.

Ipamorelin In trials Selective ghrelin receptor agonist (GHRP) that releases growth hormone without raising cortisol or prolactin.
GHRP-2 (Pralmorelin) In trials Ghrelin receptor agonist with strong GH release, but also raises cortisol, prolactin and appetite.
GHRP-6 In trials The first GHRP: ghrelin receptor agonist with marked hunger and a rise in cortisol and prolactin.
GHRP-1 In trials The least-studied member of the GHRP family; a few small human studies, no development beyond them.
Hexarelin (Examorelin) In trials Potent ghrelin receptor agonist with cardiac effects via CD36, but rapid desensitisation and raised cortisol.
Macimorelin (Macrilen, Ghryvelin) Approved Oral ghrelin receptor agonist approved as a single-dose diagnostic test for adult GH deficiency.
Anamorelin (Adlumiz) Approved Oral ghrelin receptor agonist for cancer cachexia: approved in Japan, refused by the EMA.
MK-677 (Ibutamoren, Nutrobal) In trials Not a peptide but an orally active ghrelin receptor agonist raising GH and IGF-1 around the clock.

IGF-1

The downstream messenger that carries much of GH’s growth effect (more IGF-1 analogues sit under recovery).

IGF-1 DES(1-3) Experimental A naturally occurring truncated IGF-1 that escapes its binding proteins; no human studies exist.

Somatostatin axis — suppressing GH

The opposite direction: drugs that lower GH or block its receptor, used for acromegaly and related conditions where there is too much.

Somatostatin (SRIF, SST) Natural hormone The body's own inhibitory brake on growth hormone release, and the template for octreotide and lanreotide.
Octreotide (Sandostatin) Approved Long-acting somatostatin analogue that suppresses growth hormone; standard medical therapy for acromegaly.
Lanreotide Approved Depot somatostatin analogue for acromegaly and neuroendocrine tumours, injected once every four weeks.
Pegvisomant (Somavert) Approved Growth hormone receptor antagonist for acromegaly: it blocks GH action rather than GH secretion.

Growth hormone peptides: common questions

What is the difference between a GHRH analogue and a GHRP?

They pull the same lever from two sides. A GHRH analogue (sermorelin, CJC-1295, tesamorelin) copies the hormone that tells the pituitary to release GH; a GHRP or ghrelin-receptor agonist (ipamorelin, the GHRP-2/6 family, MK-677) works through the separate ghrelin receptor. Because the two routes add up, they are often combined — see MK-677 vs ipamorelin.

Is MK-677 better than an injectable peptide like ipamorelin?

They are not really the same tool. MK-677 is an oral tablet that raises GH and IGF-1 around the clock; ipamorelin is an injection that produces a short GH pulse closer to the body’s own pattern. The full comparison sets out the trade-offs — convenience and steady IGF-1 against water retention and a less physiological signal.

Do growth-hormone peptides actually build muscle?

They reliably raise GH and IGF-1 on blood tests. Whether that turns into meaningful extra muscle or performance in healthy adults is a separate, much weaker claim — the controlled evidence for a body-composition benefit is thin, and raising a hormone level is not the same as improving an outcome. Each entry says what its trials actually measured.

Are these growth-hormone peptides legal, and are they banned in sport?

Several are approved medicines (somatropin, tesamorelin, the weekly GH analogues); the GHRPs, CJC-1295, MK-677 and sermorelin are sold as unapproved research chemicals. All of them — GH, its releasing factors and the secretagogues — are on the WADA Prohibited List (S2) and banned at all times. See doping status and legal status.

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