Growth Hormone Peptides Explained: GHRH Analogs vs GH Secretagogues

TL;DR

Growth hormone peptides explained in one line: they are short amino acid chains that signal the pituitary gland to release the body's own growth hormone (GH), instead of adding GH from outside. They split into two families: GHRH analogs (CJC-1295, tesamorelin) that copy growth hormone-releasing hormone, and GH secretagogues (ipamorelin, MK-677) that copy ghrelin. In a phase 1 study, CJC-1295 raised GH about 2 to 10 fold and IGF-1 about 1.5 to 3 fold in healthy adults (Teichman et al., JCEM 2006; doi:10.1210/jc.2005-1536). Tesamorelin, a GHRH analog approved as Egrifta, lowered visceral adipose tissue about 15 percent in a trial (Falutz et al., NEJM 2007; doi:10.1056/NEJMoa072375), while MK-677 raised GH and IGF-1 in older adults but also raised fasting glucose and lowered insulin sensitivity (Nass et al., Ann Intern Med 2008; PMID 18981485).

Growth hormone peptides explained: what are they?

Growth hormone peptides are short chains of amino acids that prompt the pituitary gland to release more of the body's own growth hormone, instead of injecting growth hormone itself.

That distinction matters. Recombinant human growth hormone (rhGH) is the hormone itself, delivered from outside. A growth hormone peptide is an upstream signal: it acts on the receptors that tell the pituitary when to release GH. The peptides in this category fall into two families, and both push on the same axis from slightly different angles. One family copies growth hormone-releasing hormone (GHRH). The other copies ghrelin, the natural GH secretagogue. Understanding those two levers is most of what growth hormone peptides explained comes down to. For the broader background on what peptides are and how they signal, see [what are peptides](/what-are-peptides).

How do growth hormone peptides work in the GH/IGF-1 axis?

They act at two control points of the GH/IGF-1 axis: the GHRH receptor and the ghrelin receptor, both of which drive the pituitary to release GH, which then tells the liver to make IGF-1.

Here is the pathway in plain terms. The hypothalamus sends two "go" signals to the pituitary: GHRH and ghrelin. It also sends a "stop" signal called somatostatin. GH comes out in pulses set by the balance of those signals. Once GH is in the blood, it acts on the liver and other tissues to produce insulin-like growth factor 1 (IGF-1), which carries out many of GH's downstream effects.

GHRH analogs bind the GHRH receptor and amplify the "go" signal. A long-acting GHRH analog kept GH and IGF-1 raised for days after a single dose in healthy adults (Teichman et al., JCEM 2006; doi:10.1210/jc.2005-1536). GH secretagogues copy ghrelin, bind a separate receptor, and were shown to trigger GH release selectively in animal models (Raun et al., Eur J Endocrinol 1998; doi:10.1530/eje.0.1390552). Because they hit different receptors, the two families are often studied together.

What is the difference between GHRH analogs and GH secretagogues?

GHRH analogs copy growth hormone-releasing hormone and bind the GHRH receptor, while GH secretagogues copy ghrelin, bind a separate receptor, and some can be taken orally.

Both families are frequently paired in research because they act on separate receptors. The [CJC-1295 and ipamorelin](/cjc-ipamorelin) guide walks through one such pairing in detail.

Why signal your own growth hormone instead of injecting it?

The rationale researchers describe is that prompting release keeps GH coming out in the body's natural pulses under its own feedback control, while injected GH is a flat, continuous signal.

Natural GH release is pulsatile, and the body regulates it with feedback loops involving IGF-1 and somatostatin. The stated logic behind GHRH analogs and secretagogues is that they work with those loops rather than overriding them, so the pituitary still governs the ceiling. This is a mechanistic rationale reported in the literature (Teichman et al., JCEM 2006; Raun et al., Eur J Endocrinol 1998), not a claim that peptides are safer or more effective than rhGH. Long-term head-to-head human data comparing the two approaches is limited.

What does research report about GHRH analogs like CJC-1295 and tesamorelin?

Research reports that CJC-1295 sustained higher GH and IGF-1 in healthy adults, and that tesamorelin lowered visceral fat in a clinical trial.

CJC-1295 is a long-acting GHRH analog. In a phase 1 study of healthy adults, single doses raised mean GH about 2 to 10 fold for 6 days or more and IGF-1 about 1.5 to 3 fold for 9 to 11 days (Teichman et al., JCEM 2006; doi:10.1210/jc.2005-1536). It is often paired with a secretagogue in research contexts; see the [CJC-1295 and ipamorelin](/cjc-ipamorelin) guide.

Tesamorelin is a GHRH analog approved as Egrifta to reduce excess visceral abdominal fat in adults with HIV-associated lipodystrophy. That approval describes a specific regulatory indication in a defined patient population; it is not a general weight or fat-loss claim for the wider public. In its pivotal trial, visceral adipose tissue fell about 15 percent versus placebo (Falutz et al., NEJM 2007; doi:10.1056/NEJMoa072375). More detail sits on the [tesamorelin](/tesamorelin) page.

What does research report about GH secretagogues like ipamorelin and MK-677?

Research reports that ipamorelin triggered selective GH release in animal models, and that oral MK-677 raised GH, IGF-1 and fat-free mass in older adults while also worsening some metabolic markers.

Ipamorelin was characterized as the first selective GH secretagogue, releasing GH with little change in prolactin or cortisol in animal models (Raun et al., Eur J Endocrinol 1998; doi:10.1530/eje.0.1390552). Human data on ipamorelin is limited, so its profile in people is less defined than the animal work suggests.

MK-677 (ibutamoren) is an oral ghrelin mimetic. In a randomized trial in healthy older adults it raised GH and IGF-1 and increased fat-free mass by about 1.1 kg over a year, but it also raised fasting glucose by about 0.3 mmol/L and lowered insulin sensitivity (Nass et al., Ann Intern Med 2008; PMID 18981485). That metabolic signal is the most cited caution for this compound.

What dose did participants receive in the cited trials?

The ranges below reflect what published studies and commonly studied research protocols report. This is educational, not a prescription or a personal recommendation.

The cited ipamorelin study (Raun et al., Eur J Endocrinol 1998) was conducted in animal models, so it does not report a human dose. Nothing here is a protocol, and any personal use question belongs with a qualified clinician.

What do studies report about body composition?

Two named findings anchor the body-composition picture: tesamorelin lowered visceral fat about 15 percent (Falutz et al., NEJM 2007), and MK-677 increased fat-free mass while shifting glucose markers (Nass et al., Ann Intern Med 2008).

Tesamorelin's effect was measured specifically on visceral adipose tissue, the deep fat around the organs, in a defined clinical population (Falutz et al., NEJM 2007; doi:10.1056/NEJMoa072375). MK-677 raised fat-free mass in older adults, but the same trial reported higher fasting glucose and lower insulin sensitivity (Nass et al., Ann Intern Med 2008; PMID 18981485), so the change did not come without trade-offs. These are reported research outcomes in study populations. They are not a promise of any result for any individual, and they do not establish that these compounds build muscle or reshape the body in a general population. For compound-specific outcome context, see [peptides for fat loss](/peptides-for-fat-loss) and [peptides for muscle growth](/peptides-for-muscle-growth).

What are the safety signals researchers have flagged?

The clearest human safety signal in this class is metabolic: MK-677 raised fasting glucose and lowered insulin sensitivity (Nass et al., Ann Intern Med 2008), and long-term human data for most GH peptides remains limited.

Because these compounds raise GH and IGF-1, researchers monitor glucose regulation and other IGF-1-linked markers. Some GHRH analogs and secretagogues have only short-term or small human datasets, and ipamorelin's human profile in particular is not well defined (its most cited characterization is animal work, Raun et al., Eur J Endocrinol 1998). Tesamorelin is the exception with a regulatory approval and pivotal trial data (Falutz et al., NEJM 2007). The responsible reading of this evidence is to treat unknowns as unknowns and route any personal use question to a qualified clinician.