GH Secretagogues Compared: Hexarelin, Ipamorelin, Sermorelin, CJC-1295, Tesamorelin and MK-677

Growth hormone secretagogues all end up in the same place — more circulating growth hormone (GH) and, downstream, more IGF-1. How they get there is what separates them. Some are analogues of growth hormone-releasing hormone (GHRH) and work on the pituitary’s GHRH receptor. Others are ghrelin analogues and work on the growth hormone secretagogue receptor (GHS-R). The receptor a compound binds is what predicts its shape of GH release, its half-life and its off-target behaviour.

This article compares the compounds researchers most often put side by side: hexarelin, ipamorelin, GHRP-2, MK-677, sermorelin, CJC-1295 and tesamorelin.

Key Takeaways

• GHRH analogues (sermorelin, CJC-1295, tesamorelin) extend the duration of GH peaks and preserve pulsatility.
• Ghrelin-receptor agonists (ipamorelin, hexarelin, GHRP-2, MK-677) produce sharp, short-lived GH surges.
• Ipamorelin is the most receptor-selective of the ghrelin analogues; hexarelin and GHRP-2 carry more off-axis endocrine activity.
• Half-lives range from roughly five minutes (sermorelin) to several days (CJC-1295 with DAC).
• Combining one compound from each class produces GH elevations that neither achieves alone in published models.
• All of these compounds are supplied for laboratory research only and none is approved for human use in that context.

What Is a Growth Hormone Secretagogue?

A growth hormone secretagogue is a compound that prompts the pituitary to release its own GH rather than supplying GH from outside. That distinction matters in study design. Exogenous GH bypasses the body’s feedback loop and produces an artificial square-wave profile; a secretagogue works through the existing loop, so the pulsatile rhythm is preserved and the system retains its own brake.

Endogenous GH declines steeply with age — roughly halving between 20 and 40 in the published data, and falling far further by 80 — which is why the GH/IGF-1 axis is a recurring subject in ageing research.⁴

Two Receptors, Two Behaviours

GHRH receptor. Sermorelin, CJC-1295 and tesamorelin bind GHRH receptors in the anterior pituitary. GHRH receptors are not widely expressed outside the pituitary, so the direct action of these compounds stays confined to GH stimulation. The result in published models is a longer GH peak and a raised baseline rather than a supraphysiological spike.

Growth hormone secretagogue receptor (GHS-R). Ipamorelin, hexarelin, GHRP-2 and MK-677 mimic ghrelin at GHS-R. GHS-R subtypes are distributed across the central nervous system as well as the pituitary, which is why this class is also studied in relation to appetite, sleep architecture, glucose handling, cognition and pain modulation. GH release is rapid — typically within 5 to 15 minutes in experimental settings — and falls away quickly. Comparative work reports plasma GH rising several-fold above baseline after ghrelin-analogue administration, and both classes acting synergistically with each other.¹⁰

How Do the Compounds Compare?

The GHRH Analogues

Sermorelin

Sermorelin is GHRH fragment 1-29 — the biologically active core of the parent hormone, often written GRF(1-29). It binds GHRH receptors with high affinity at very low concentrations. In published work it raises baseline GH and lengthens peak duration while leaving the normal pulsatile rhythm intact. Its half-life is around five minutes, limited by enzymatic degradation and renal clearance.

Because it works through the intact feedback loop rather than around it, models using sermorelin do not show the receptor downregulation (tachyphylaxis) associated with sustained exogenous GH exposure.

CJC-1295

CJC-1295 is the same GHRH 1-29 backbone with amino acid substitutions that resist enzymatic cleavage, pushing the half-life to roughly 30 minutes in its base form.

The naming is a persistent source of confusion. “CJC-1295” is used both for the modified 1-29 peptide and for the version carrying a Drug Affinity Complex. The DAC version binds plasma albumin and circulates for several days, which changes the whole experimental profile. The sequence and the presence or absence of DAC should be confirmed from the analysis certificate rather than the product name.

Tesamorelin

Tesamorelin is a GHRH analogue whose research record centres on visceral adiposity. Reported effects include prolonged GH peak duration without a large rise in maximal GH release, with a metabolic profile close to sermorelin but a different body-composition outcome — a stronger fat-reduction signal, particularly visceral, alongside lean mass preservation. Additional exploratory work covers bone quality, peripheral nerve regeneration and cognitive measures.

The Ghrelin-Receptor Agonists

Ipamorelin

Ipamorelin is a pentapeptide (Aib-His-D-2Nal-D-Phe-Lys, ~712 g/mol) and the most selective ghrelin receptor agonist in common research use. Its selectivity is the point: published studies report GH release without meaningful changes in prolactin, FSH, LH, TSH or ACTH, which makes it useful for isolating the effects of GH elevation from everything else a less selective secretagogue would trigger.

Ipamorelin’s strongest preclinical signal is skeletal. Svensson and colleagues reported increased bone mineral content in adult female rats, and Andersen and colleagues reported that ipamorelin counteracted a glucocorticoid-induced decrease in bone formation.³,⁷

Hexarelin

Hexarelin (examorelin) is a hexapeptide — one residue longer than ipamorelin, and that difference redirects its secondary biology toward the heart. Xu and colleagues reported attenuated cardiac fibrosis in spontaneously hypertensive rats after chronic administration, and Huang and colleagues reported protection of rat cardiomyocytes from ischaemia/reperfusion injury through interleukin-1 signalling.⁵,⁸ Mao and colleagues studied hexarelin after myocardial infarction in ghrelin knockout mice, separating its cardiac activity from ghrelin signalling itself.⁶

Hexarelin has also been examined outside the heart: Sirago and colleagues reported protection of skeletal muscle from mitochondrial damage in a rat model of cisplatin-induced cachexia, and Mosa and colleagues reported improved lipid metabolic measures in insulin-resistant MKR mice.¹,⁹

GHRP-2

GHRP-2 binds the same receptor as ipamorelin but is less selective. Acting on GHS-R in both hypothalamus and pituitary, it triggers direct GH release and also stimulates GHRH release — a dual action that raises its potency and its off-axis activity, including appetite stimulation, at the same time. Where a study needs a clean GH signal, ipamorelin is the more common choice; where potency matters more than selectivity, GHRP-2 appears instead.

MK-677 (Ibutamoren)

MK-677 is not a peptide at all. It is an orally bioavailable non-peptide agonist at GHSR-1a with a half-life near 24 hours.

Its distinguishing findings are sleep and appetite. Published work reports improved REM and slow-wave sleep and reduced REM latency — the clearest sleep-architecture signal in this class — alongside increased appetite, water retention and bone turnover markers. Glucose and insulin measures are the ones to watch in study design.

How Do Hexarelin and Ipamorelin Differ?

These two are compared most often because they are structurally closest and behave differently anyway.

Bone. Ipamorelin carries the stronger skeletal record, with increased bone mineral content and bone formation reported in rodent models.³,⁷

Cardiac tissue. Hexarelin carries the stronger cardiac record — fibrosis attenuation, cardiomyocyte protection in ischaemia/reperfusion, and post-infarction work in ghrelin knockout animals.⁵,⁶,⁸

Neurogenesis and cognition. Both have been examined in memory and neurogenesis models, reflecting the wide central distribution of GHS-R subtypes.

Pain modulation. GHS-R activity in the central nervous system has been studied in relation to nociception, an effect distinct from GH release.

The GH/IGF-1 axis with age. Frutos and colleagues examined whether GH secretagogues can reverse the age-related decline in the GH/IGF-1 axis, one of the more direct tests of the ageing hypothesis behind this class.⁴

Why Are the Two Classes Combined?

Because they act on different receptors, a GHRH analogue and a ghrelin agonist act additively rather than competing. The pairing most often studied is CJC-1295 with ipamorelin: the GHRH analogue lifts and lengthens the peak, the ghrelin agonist raises its amplitude, and published models report combined GH elevations that neither compound reaches alone.

Tannenbaum and colleagues mapped the underlying interplay between ghrelin, somatostatin and GHRH in the regulation of pulsatile GH secretion — the mechanism that makes the combination additive rather than redundant.¹⁰

How Should Research Material Be Verified?

Naming is the weak point in this category. CJC-1295 with and without DAC share a name, sermorelin and CJC-1295 share a backbone, and “GHRP” covers several distinct hexapeptides.

Confirm the sequence, not the label. A Certificate of Analysis from an independent laboratory, tied to the specific lot, should state identity and purity and carry a batch number so results trace back to the material used.

Store the lyophilised form correctly. Freeze-dried powder is the most stable state — cool, dry and out of direct light, refrigerated for longer storage. Reconstituted material is far less stable and should stay refrigerated and be used within a defined window.

What Is Still Unknown?

Most of the comparative evidence in this article comes from rodent models and early-phase human work. Direct head-to-head human trials between these compounds are scarce, which means the class rankings above describe published observations in specific models rather than settled facts.

Open questions include how the shape of GH release — a longer plateau against a sharper spike — translates to downstream IGF-1 exposure over time, whether the receptor selectivity advantage of ipamorelin holds at higher exposures, how the combination approaches behave over extended periods, and what the metabolic consequences of sustained GHS-R activation are. Regulatory status should not be read as evidence of safety or effectiveness in either direction.

Frequently Asked Questions

What Is the Difference Between a GHRH Analogue and a Ghrelin Agonist?

They bind different receptors. GHRH analogues (sermorelin, CJC-1295, tesamorelin) act on GHRH receptors in the pituitary and lengthen the GH peak. Ghrelin agonists (ipamorelin, hexarelin, GHRP-2, MK-677) act on GHS-R and produce a fast, short spike. The two classes are additive because the pathways are separate.

Which Secretagogue Is the Most Selective?

Ipamorelin. Published studies report GH release without meaningful changes in prolactin, ACTH, cortisol, FSH, LH or TSH, which is why it is used when a study needs to isolate GH effects.

Is CJC-1295 the Same With and Without DAC?

No. The base peptide has a half-life of roughly 30 minutes; adding the Drug Affinity Complex binds it to albumin and extends circulation to several days. They behave differently enough that the two should never be treated as interchangeable.

How Do Secretagogues Differ From Exogenous Growth Hormone?

Exogenous GH is supplied directly and bypasses the feedback loop, producing a square-wave profile. Secretagogues prompt the pituitary to release its own GH, so pulsatility and the body’s own regulatory brake remain in place. This is the central reason the class is studied at all.

Why Is MK-677 Grouped With Peptides?

Because of the receptor, not the chemistry. MK-677 is a non-peptide small molecule, but it activates the same GHSR-1a receptor as the ghrelin-analogue peptides — with oral bioavailability and a roughly 24-hour half-life instead.
Disclaimer: Licensed Peptides products are supplied strictly for laboratory research purposes only. They are not intended for human consumption, clinical use, therapeutic application, diagnosis, treatment, cure, or prevention of any disease. This article is provided for educational and scientific discussion purposes only. All references to biological activity relate exclusively to laboratory, in vitro, and preclinical research.

References

1. Sirago G, Conte E, Fracasso F, et al. Growth hormone secretagogues hexarelin and JMV2894 protect skeletal muscle from mitochondrial damages in a rat model of cisplatin-induced cachexia. Sci Rep. 2017;7(1):13017. doi:10.1038/s41598-017-13504-y. PMID:29026190; PMCID:PMC5638899.
2. Djurhuus CB, Hansen TK, Møller N, et al. Growth hormone and growth hormone secretagogue effects on nitrogen balance and urea synthesis in steroid treated rats. Growth Horm IGF Res. 2009. doi:10.1016/j.ghir.2009.01.001
3. Svensson J, Lall S, Dickson SL, et al. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. J Endocrinol. 2000;165(3):569–577. doi:10.1677/joe.0.1650569. PMID:10828840.
4. Frutos MG, Cacicedo L, Fernández C, et al. Insights into a role of GH secretagogues in reversing the age-related decline in the GH/IGF-I axis. Am J Physiol Endocrinol Metab. 2007;293(5):E1140–E1152. doi:10.1152/ajpendo.00236.2007. PMID:17684105.
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6. Mao Y, Tokudome T, Kishimoto I, et al. Hexarelin treatment in male ghrelin knockout mice after myocardial infarction. Endocrinology. 2013;154(10):3847–3854. doi:10.1210/en.2013-1291
7. Andersen NB, Malmlöf K, Johansen PB, et al. The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats. Growth Horm IGF Res. 2001;11(5):266–272. doi:10.1054/ghir.2001.0239. PMID:11735244.
8. Huang J, Li Y, Zhang J, Liu Y, Lu Q. The growth hormone secretagogue hexarelin protects rat cardiomyocytes from in vivo ischemia/reperfusion injury through interleukin-1 signaling pathway. Int Heart J. 2017;58(2):257–263. doi:10.1536/ihj.16-241. PMID:28321024.
9. Mosa R, Huang L, Wu Y, et al. Hexarelin, a growth hormone secretagogue, improves lipid metabolic aberrations in nonobese insulin-resistant male MKR mice. Endocrinology. 2017;158(10):3174–3187. doi:10.1210/en.2017-00168. PMID:28977588; PMCID:PMC5659698.
10. Tannenbaum GS, Epelbaum J, Bowers CY. Interrelationship between the novel peptide ghrelin and somatostatin/growth hormone-releasing hormone in regulation of pulsatile growth hormone secretion. Endocrinology. 2003;144(3):967–974. doi:10.1210/en.2002-220852. PMID:12586774.