GHRP-2: Sequence, Receptor and What the Research Shows

GHRP-2 is one of the older synthetic growth hormone secretagogues, and most of what gets written about it online is recycled and vague. So here’s the grounded version. GHRP-2, also named pralmorelin, is a synthetic six-residue peptide that binds GHS-R1a, the growth hormone secretagogue receptor. We’ll stick to what the primary literature actually measured: the sequence, the receptor, how it reads against the stress axis, and what the provocative-testing studies found. Every claim links straight to its abstract.

What GHRP-2 is

GHRP-2 is a synthetic hexapeptide, D-Ala-D-beta-Nal-Ala-Trp-D-Phe-Lys-NH2. Those D-amino acids and the C-terminal amide are what make it shrug off quick proteolysis, which is why it reads consistently from one assay to the next. It’s a non-glycosylated chain of six residues, supplied as a lyophilized powder. Here’s a detail that throws people who’ve handled it: the vial can look empty, or barely dusted, because there’s no filler in there, yet it still holds the stated amount of peptide. And one more thing worth keeping straight, because labels blur it. Molecular mass, peptide identity and purity are three different measurements. A batch certificate should spell out each, not fold them into a single “purity” figure.

The receptor, and its late arrival

GHRP-2 belongs to the growth hormone secretagogue family, and it acts at GHS-R1a, not at the separate GHRH receptor. The two aren’t interchangeable. The receptor has a strange history too. The GHRPs were studied for years before anyone had the target in hand. GHS-R1a finally got cloned in 1996 [2], and ghrelin, the body’s own ligand, turned up in stomach extracts in 1999 [3]. That gap is a handy lens for the old literature. A paper from the early 1990s describing GHRP-2 was working blind on mechanism, so read its claims with that in mind.

What the pharmacology work measured

In Raun’s 1998 comparison across cells, rats and swine, GHRP-2 came out more potent than GHRP-6 and ipamorelin, but with a lower maximum GH response in the swine model [1]. Ferro’s structure-activity study then pinned the shared Ala-Trp-(D-Phe)-Lys core as the stretch these peptides need to grab GHS-R1a, and showed intact GHRP-2 plus active metabolites binding the receptor in excretion samples [7]. If you’re comparing potency numbers across papers, check the model and the assay first. A value from a receptor-binding test and one from a conscious animal are not the same thing.

GHRP-2 and the stress axis

GHRP-2 isn’t a clean, selective tool. In Raun’s swine work, GHRP-2 and GHRP-6 both raised plasma ACTH and cortisol, while ipamorelin left them flat [1]. Arvat’s human study says the same: in young adults, GHRP-2 lifted prolactin, ACTH and cortisol, with the ACTH and cortisol rise about on par with hCRH [4]. None of this is buried in the data, and it’s the single thing that most separates GHRP-2 from the more selective secretagogues once you line the endpoints up. Want that contrast spelled out? See our GHRP-2 versus ipamorelin comparison.

GH-axis endpoints

Two studies anchor the GH-axis picture. In the 2001 GHRH-receptor-mutation work, GHRP-2 drove roughly a 4.5-fold GH rise in affected patients, far under the 79-fold response in controls but clearly above baseline, with ACTH, cortisol and prolactin unchanged [5]. The authors argued that an intact GHRH signal isn’t strictly needed for GHRP-2 to act on somatotrophs. The 2024 adolescent series showed the split that makes GHRP-2 handy in provocative testing: median GH peaks near 89 to 90 ng/mL in idiopathic and short-stature groups against 3.4 ng/mL in the organic or genetic GH-deficient group [6]. That same report tacked on a caution that’s easy to skim past. Two patients cleared the cutoff on the GHRP-2 test but fell below it on other tests, so the authors floated that the GHRP-2 threshold in adolescents may need another look [6]. A stimulation number only means something next to the specific cutoff and protocol behind it.

Species differences are real

Here’s something the old write-ups tend to skate over. GHRP-2’s effects don’t carry cleanly from one species to the next. Somatotroph characteristics differ between rodents, swine and humans, so the size of the GH response, how much ACTH and cortisol get pulled in, and the shape of the time course can all shift with the model. Raun’s swine data and Arvat’s human data don’t really contradict each other. They describe different systems [1][4]. Pull a number out of a GHRP-2 paper, and carry the species and the sampling schedule along with it, or the comparison quietly falls apart.

The swine potency numbers

If you’d rather have figures than adjectives, Raun’s conscious-swine data are the cleanest. GHRP-2 switched on at a low concentration, ED50 around 0.6 nmol/kg, but its maximal GH response topped out near 56 ng/mL. For contrast, ipamorelin’s ED50 was near 2.3 nmol/kg with a maximum around 65 ng/mL, and GHRP-6 landed close by at 3.9 nmol/kg and 74 ng/mL [1]. So GHRP-2’s signature in that model is high potency with a lower ceiling. Potency and maximal effect are separate properties, and squashing them into “stronger” tosses out the part that usually matters most.

Handling and characterization

Because GHRP-2 ships lyophilized, the practical notes are all about stability. Keep it desiccated and cold so it doesn’t pull moisture, and reconstitute it in an appropriate aqueous laboratory solution when you prep an experiment. Identity and purity should come from the batch’s own analytics, typically HPLC for purity and mass spectrometry for identity, not from a guess. For how that testing gets structured upstream of any study, see our note on third-party tested peptides.

FAQ

Is GHRP-2 the same as pralmorelin? Yes, pralmorelin is just another name for GHRP-2 [4].

What receptor does GHRP-2 act on? GHS-R1a, the growth hormone secretagogue receptor, which is separate from the GHRH receptor [1].

Does GHRP-2 hit hormones other than GH? In published work it also raised prolactin, ACTH and cortisol, unlike the more selective ipamorelin [4].

References

1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998. https://pubmed.ncbi.nlm.nih.gov/9849822/
2. Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996. https://pubmed.ncbi.nlm.nih.gov/8688086/
3. Kojima M, Hosoda H, Date Y, et al. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999. https://pubmed.ncbi.nlm.nih.gov/10604470/
4. Arvat E, di Vito L, Maccagno B, et al. Effects of GHRP-2 and hexarelin, two synthetic GH-releasing peptides, on GH, prolactin, ACTH and cortisol levels in man. Peptides. 1997. https://pubmed.ncbi.nlm.nih.gov/9285939/
5. Gondo RG, Aguiar-Oliveira MH, Hayashida CY, et al. Growth hormone-releasing peptide-2 stimulates GH secretion in GH-deficient patients with mutated GH-releasing hormone receptor. J Clin Endocrinol Metab. 2001. https://pubmed.ncbi.nlm.nih.gov/11443201/
6. Onuki T, Hiroaki T, Sawano K, et al. Robust growth hormone responses to GH-releasing peptide 2 in adolescents. J Pediatr Endocrinol Metab. 2024. https://pubmed.ncbi.nlm.nih.gov/38958228/
7. Ferro P, Krotov G, Zvereva I, et al. Structure-activity relationship for peptidic growth hormone secretagogues. Drug Test Anal. 2017. https://pubmed.ncbi.nlm.nih.gov/26811125/