what is the difference
Ipamorelin, GHRP-2 and GHRP-6
Three short peptides acting at the same receptor, sold as near-substitutes, whose published records were built to answer three questions that have almost nothing to do with each other.
Ipamorelin is a five amino acid peptide at the growth hormone secretagogue receptor, the target the hunger hormone ghrelin acts on. GHRP-2, also called pralmorelin, and GHRP-6 are six amino acid peptides at the same receptor, characterised alongside it in the 1990s. All three prompt the pituitary to release growth hormone, which is why they are sold as versions of one another.
What separates them is what else they move, and what has been asked about each in a person. Ipamorelin's distinguishing published result is about selectivity. GHRP-2 holds an approval in Japan, and it is an approval as a single-use diagnostic test rather than as a therapy. GHRP-6's human record is three small studies about sleep, hormones and how fast the molecule clears. This page sets the three records side by side.
Not medical advice
This page reports what has been documented about a compound. It is not medical advice, not a diagnosis, not a dosing protocol, and not a recommendation to obtain or use anything described here. Talk to a licensed clinician about anything concerning your health. Read the full disclaimer.
Reviewed against editorial standards Updated
The short answer
The three are not interchangeable, and the reason is what each one releases alongside growth hormone. In conscious swine, GHRP-6 and GHRP-2 raised ACTH and cortisol while ipamorelin did not, at exposures more than two hundred times the level that released growth hormone [1]. That comparison is the origin of every selectivity claim made for ipamorelin, and it was run in pigs and rats by the laboratory that developed it.
Their human records diverge just as sharply. On 2 August 2026 the registry returned three registrations for ipamorelin, none for GHRP-2 under either of its names, and none for GHRP-6 [8]. The one published ipamorelin trial asked whether a bowel started moving faster after surgery, and it did not reach significance [2].
Side by side
| Property | Ipamorelin | GHRP-2 | GHRP-6 |
|---|---|---|---|
| What it is | A five amino acid peptide at the growth hormone secretagogue receptor | A six amino acid peptide at the same receptor, also called pralmorelin | A six amino acid peptide at the same receptor, one of the original growth hormone releasing peptides |
| What the pharmacology comparison found | Released growth hormone with a potency close to GHRP-6 and did not raise ACTH or cortisol, at exposures more than two hundred times the growth-hormone-releasing level [1] | Raised ACTH and cortisol in the same conscious swine experiment [1] | Raised ACTH and cortisol in the same experiment, and in healthy men across the first half of the night [1] [4] |
| Species that comparison was run in | Pigs and rats, by the laboratory that developed the compound [1] | The same pigs and rats [1] | The same pigs and rats, plus one small human study [1] [4] |
| Registered human trials | 3, two of them phase 2 in postoperative ileus [8] | 0, under GHRP-2 and under pralmorelin [8] | 0 [8] |
| Published human record | One completed multicentre trial, double blind against placebo, in 117 adults having open or laparoscopic bowel resection, 114 in the analysis population [2] | A diagnostic validation study in 77 healthy subjects and 58 patients with a peak growth hormone below 3 micrograms per litre on the insulin tolerance test [3] | One placebo-controlled overnight hormone and sleep study in healthy men [4], and one pharmacokinetic study in nine healthy men [6] |
| What that record reported | Median time to tolerating a standardised solid meal was 25.3 hours against 32.6 hours on placebo, which did not reach significance at p equals 0.15, and no secondary efficacy analysis separated the arms [2] | Peak growth hormone reached 1.36 micrograms per litre in the patients and 84.6 in the healthy group, a difference of better than sixty fold at p below 0.001, which is what makes it usable as a test [3] | Growth hormone rose, ACTH and cortisol rose across the first half of the night, stage 2 sleep increased and slow wave sleep did not change [4]. Distribution half-life about 7.6 minutes, elimination half-life about 2.5 hours [6] |
| Approval status | Not approved in the United States and not on the 503A Bulks List [7] | Approved in Japan as a single-use diagnostic agent for growth hormone deficiency rather than as a therapy. Not approved in the United States | Unapproved everywhere, and it holds no diagnostic approval of the kind GHRP-2 has in Japan |
| What has never been measured for it | Body composition, recovery or ageing. Nothing has been registered or published on any of them | Anything beyond a single provocative administration in a clinic. No study has followed anyone taking it for weeks | Appetite in a person in a published study. The rodent experiment behind the reputation delivered it into the brain ventricles [5] |
| FDA 503A position | Ipamorelin acetate and ipamorelin free base went before the Pharmacy Compounding Advisory Committee on 29 October 2024, for growth hormone deficiency and postoperative ileus, under docket FDA-2024-N-4188 [7] | Not on the 503A Bulks List | Not on the 503A Bulks List |
| WADA 2026 position | Reached under class S2, growth hormone secretagogues, prohibited at all times [9] | Reached under the same class [9] | Reached under the same class [9] |
Why the two get mixed up
One receptor produces one sales pitch. All three act at the growth hormone secretagogue receptor, all three raise growth hormone, and a listing that says so has said everything the three have in common. From there they get presented as grades of one product, with ipamorelin as the mild option and GHRP-6 as the strong one, which describes a dial the published work does not contain.
The naming pattern helps the collapse along. GHRP-2 and GHRP-6 share a prefix and differ by a numeral, which reads as two versions of one thing rather than two separately characterised molecules. Ipamorelin sits outside that scheme and gets compared to both anyway, usually on the one axis where a published comparison exists.
That comparison has been run once, and it is worth being exact about where. A 1998 paper in the European Journal of Endocrinology set the secretagogues against each other in conscious swine and in rats [1]. It is a real finding and it belongs to a pig. No human head to head between ipamorelin and GHRP-2 on cortisol has been published, so the comparison every product page makes rests on animal pharmacology.
What the published record covers for each
The selectivity result is the best-supported thing said about ipamorelin, and its limits are in its design. In conscious swine, ipamorelin released growth hormone with a potency close to GHRP-6; none of the secretagogues tested moved FSH, LH, prolactin or TSH; and while GHRP-6 and GHRP-2 raised ACTH and cortisol in the same animals, ipamorelin did not, at exposures more than two hundred times the level that released growth hormone [Animal] [1]. These results come from pigs and rats in a laboratory pharmacology model, published by the group that developed the molecule. An animal model is a deliberate simplification, and mechanism in a pig does not establish an effect in people.
Ipamorelin's own human record is one completed trial and it is about the gut. A multicentre, double blind, placebo-controlled study in adults having open or laparoscopic bowel resection enrolled 117 with 114 in the analysis population, and reported a median time to tolerating a standardised solid meal of 25.3 hours against 32.6 hours on placebo, which did not reach significance at p equals 0.15; no secondary efficacy analysis separated the arms [Human RCT] [2]. The phase 2 programme did not continue, and nothing has been registered or published on body composition, recovery or ageing for this compound.
GHRP-2's human literature was built to answer a yes or no question about a pituitary, and one number in it cuts directly against the way the compound is sold. In the validation study, 77 healthy subjects and 58 patients with a peak growth hormone below 3 micrograms per litre on the insulin tolerance test were sampled for two hours after a single intravenous administration. Peak growth hormone reached 1.36 micrograms per litre in the patients and 84.6 in the healthy group, a difference of better than sixty fold at p below 0.001 [Human open-label] [3]. That gap is what makes the compound usable as a test: the response is smallest in exactly the population whose growth hormone axis has declined, and largest in people whose axis is intact.
GHRP-6 has one placebo-controlled human study of what it does. Repetitive intravenous boluses were compared against placebo in healthy men, with hormones sampled from 20.00 to 07.00 and sleep recorded by EEG. Growth hormone rose, and so did ACTH and cortisol across the first half of the night, which is the opposite direction from what growth hormone releasing hormone does to cortisol; stage 2 sleep increased and slow wave sleep did not change [Human RCT] [4]. A separate study in nine healthy men measured the peptide in plasma by mass spectrometry, fitting a two-compartment model with a distribution half-life of about 7.6 minutes and an elimination half-life of about 2.5 hours [6]. That describes how quickly the molecule leaves, and nothing else.
The hunger effect GHRP-6 is known for was established in rats, and the route is the whole story. The peptide was delivered directly into the brain ventricles, which stimulated eating without affecting plasma growth hormone responses [Animal] [5]. Two things follow. The feeding effect and the growth hormone effect were separable in that model, so one is not evidence for the other. And intracerebroventricular delivery is not a route anyone uses. No published human study measuring appetite after GHRP-6 was found for this page, so the accounts of hunger that circulate are community reports. That is a statement about what has not been measured, so it carries no tier of its own.
Our takeOne receptor, three molecules, and three records that never met. The selectivity difference is real and it belongs to a pig experiment; the only completed human trial in the group asked about postoperative bowels and missed; and the compound with an actual approval holds it as a one-off diagnostic test whose central number argues against the pitch.
Frequently asked questions
What actually separates ipamorelin from GHRP-2 and GHRP-6?
One measured difference, in one experiment. In conscious swine, GHRP-6 and GHRP-2 raised ACTH and cortisol while ipamorelin did not, at exposures more than two hundred times the level that released growth hormone, and none of the secretagogues tested moved FSH, LH, prolactin or TSH [1]. That study was run in pigs and rats by the laboratory that developed ipamorelin. No human head to head between them on cortisol has been published.
How many registered trials does each one have?
On 2 August 2026 the registry returned three registrations for ipamorelin, two of them phase 2 in postoperative ileus, and zero for GHRP-2 under either of its names and zero for GHRP-6 [8].
What did the ipamorelin trial find?
Median time to tolerating a standardised solid meal was 25.3 hours against 32.6 hours on placebo, which did not reach significance at p equals 0.15, and no secondary efficacy analysis separated the arms [2]. The phase 2 programme did not continue.
Is GHRP-2 an approved medicine?
In Japan it is approved as a diagnostic agent for growth hormone deficiency, given once to answer a yes or no question about a pituitary. It is not approved as a therapy anywhere and it is not approved in the United States. The distinction matters because the whole human literature on the compound was built for that single-administration purpose [3].
Does GHRP-6 really cause hunger?
The rat experiment behind that reputation delivered the peptide directly into the brain ventricles, which stimulated eating without affecting plasma growth hormone responses [5]. No published human study measuring appetite after GHRP-6 was found for this page, which means the human accounts in circulation are community reports rather than measurements.
Are all three banned in sport?
All three are reached by class S2 of the 2026 WADA Prohibited List, covering growth hormone secretagogues, and that class is prohibited at all times, in and out of competition [9].
References
- Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998. PMID 9849822 DOI 10.1530/eje.0.1390552
- Beck DE, Sweeney WB, McCarter MD, Ipamorelin 201 Study Group. Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis. 2014. PMID 25331030 DOI 10.1007/s00384-014-2030-8
- Chihara K, Shimatsu A, Hizuka N, Tanaka T, Seino Y, Katofor Y, KP-102 Study Group. A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency. Eur J Endocrinol. 2007. PMID 17609397 DOI 10.1530/EJE-07-0066
- Frieboes RM, Murck H, Maier P, Schier T, Holsboer F, Steiger A. Growth hormone-releasing peptide-6 stimulates sleep, growth hormone, ACTH and cortisol release in normal man. Neuroendocrinology. 1995. PMID 7617137 DOI 10.1159/000126883
- Locke W, Kirgis HD, Bowers CY, Abdoh AA. Intracerebroventricular growth-hormone-releasing peptide-6 stimulates eating without affecting plasma growth hormone responses in rats. Life Sci. 1995. PMID 8614257 DOI 10.1016/0024-3205(95)00087-9
- Cabrales A, Gil J, Fernández E, Valenzuela C, Hernández F, García I, Hernández A, Besada V, Reyes O, Padrón G, Berlanga J, Guillén G, González LJ. Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. Eur J Pharm Sci. 2013. PMID 23099431 DOI 10.1016/j.ejps.2012.10.006
- US Food and Drug Administration. Pharmacy Compounding Advisory Committee; notice of meeting; establishment of a public docket; request for comments: bulk drug substances nominated for inclusion on the section 503A Bulk Drug Substances List; revisions to the Withdrawn or Removed List. Meeting held 29 October 2024. Docket No. FDA-2024-N-4188. The substances discussed were ibutamoren mesylate, L-theanine, ipamorelin acetate, ipamorelin free base and kisspeptin-10. Federal Register, volume 89, number 181, document 2024-21241. 2024. Meeting notice
- US National Library of Medicine, ClinicalTrials.gov. Registry counts run through API v2 on 2 August 2026: ipamorelin 3 studies, GHRP-2 0, pralmorelin 0 and GHRP-6 0. ClinicalTrials.gov. 2026. Registry search
- World Anti-Doping Agency. The 2026 Prohibited List, international standard, effective 1 January 2026. WADA. 2026. Prohibited List