GHRP-2 and GHRP-6 are usually discussed as interchangeable versions of one idea. The primary records separate them sharply: one became a licensed diagnostic in Japan, the other has the larger literature and no approval anywhere.
The two molecules
| GHRP-6 | GHRP-2 | |
|---|---|---|
| Other names | — | Pralmorelin, KP-102 |
| Sequence | His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 | D-Ala-D-(2-naphthyl)Ala-Ala-Trp-D-Phe-Lys-NH2 |
| Formula / weight (PubChem) | C46H56N12O6 / 873.0 | C45H55N9O6 / 818.0 |
| Target | Ghrelin receptor (GHSR) | Ghrelin receptor (GHSR) |
| Approved anywhere | No register found | Japan, diagnostic only |
| US status | Not approved; on FDA's 503B risk list (2023) | Not approved; on FDA's 503B risk list (2023) |
| Human pharmacokinetic study | Yes — Havana, 2013 | None found |
| PubMed records (3 Oct 2026) | 638 | 205 (+15 as pralmorelin) |
| ClinicalTrials.gov studies | 0 | 0 |
The last four residues are identical. The difference is at the front: GHRP-2 replaces GHRP-6's histidine and D-tryptophan with D-alanine and D-naphthylalanine, a residue that does not occur in proteins. FDA's 2023 entry flags that unnatural amino acid as adding "to the complexity of peptide characterization."
Regulatory status: a test dose in Japan, nothing elsewhere
Japan's approval is specific. KEGG DRUG lists pralmorelin hydrochloride under the brand name "GHRP" as a Japanese product in therapeutic category 7223, diagnostic reagents for endocrine function, and in Japan's list of new active ingredients. It is used as a single intravenous dose — 100 micrograms in the published analytical literature — to provoke and measure growth hormone release when pituitary reserve is in question. A 2026 Japanese study on this site's GHRP-2 dosage page used the same test to help distinguish causes of adrenal insufficiency.
GHRP-6 has no comparable entry in the registers this site checked. Its human record comes largely from Cuba's Center for Genetic Engineering and Biotechnology and from 1990s Italian and American endocrinology groups, none of which led to a licence. Neither compound appears on ClinicalTrials.gov under any of its names, which says as much about where the research was done as about how much exists — Japanese and Cuban studies register elsewhere.
The potency comparison in people
The head-to-head human data are old and small. Bowers, at Tulane University Medical Center, reported in 1993 that GHRP-6, GHRP-1 and GHRP-2 "have been found to be increasingly more effective in releasing GH in humans," that all three released more growth hormone than GHRH, and that all three worked after oral administration — near-maximal release after oral GHRP-1 and GHRP-2. A 1997 review from Turin described GHRP-6 as "the first hexapeptide to be extensively studied in humans," and a Turin study the same year called GHRP-2 and hexarelin "super-analogs of GHRP-6."
That 1997 study (six young adults, 1–2 µg/kg intravenously) also found the class is not growth-hormone-specific: GHRP-2 raised prolactin, ACTH and cortisol, with the ACTH and cortisol response similar to that from CRH. "More potent" in these papers means more growth hormone released in a laboratory session. None measured a health or body-composition outcome.
What FDA's 2023 risk list says about each
Both compounds sit on FDA's list of bulk drug substances that may present significant safety risks, with entries dated 29 September 2023 under the outsourcing-facility (503B) framework. The entries differ:
- GHRP-2 (injectable and nasal routes): immunogenicity risk from aggregation and peptide-related impurities; and "reports of serious adverse advents [sic] in patients who received GHRP-2, including increased insulin requirement to maintain the blood glucose level, death of critically ill study subjects, infection and pancreatitis, though causality has not been established."
- GHRP-6: immunogenicity risk "for certain routes of administration," limited safety information overall, and "potential effect on cortisol and increase in blood glucose due to decreases in insulin sensitivity."
The two entries agree on the theme that matters most for people with diabetes or insulin resistance: both point at glucose control, from different directions. openFDA's adverse-event database returned five reports naming "GHRP" on 3 October 2026 — too few to compare the two.
Pharmacokinetics: one measured, one not
GHRP-6 has the only human pharmacokinetic study of the pair: nine healthy men in Havana given 100, 200 and 400 µg/kg intravenously (Cabrales 2013), with a distribution half-life of 7.6 minutes and an elimination half-life of 2.5 ± 1.1 hours, plus unexplained concentration spikes in four of the nine. The details, and why per-kilogram trial doses and the 93 µg diagnostic dose are not versions of each other, are on our GHRP-6 dosage page. No human pharmacokinetic study of GHRP-2 turned up in the sources read for its page — an odd gap for the one of the two with an approval, and one explained partly by doping laboratories' statement that such volunteer studies are often not permitted.
The citation trap
PMID 9661608 is a GHRP-2 trial: six prepubertal children with growth hormone deficiency, given 0.3, 1.0 and 3.0 µg/kg/day subcutaneously over successive two-month periods. It is routinely cited as GHRP-6 evidence. Any page that quotes a "GHRP-6 dose from a pediatric trial" is very likely quoting this study under the wrong name. Both of this site's GHRP pages and Peptide Lexicon's GHRP-2 and GHRP-6 entries carry the correction.
What is not established
No trial has compared GHRP-2 and GHRP-6 over weeks, at any dose, for any outcome. The widely repeated claim that GHRP-6 causes markedly more hunger than GHRP-2 did not trace to a head-to-head human study in the sources read for this page. Neither has a measured adverse-event rate from repeated use. The performance framing of both compounds, and their anti-doping status, are covered on MuscleLedger's GHRP-2 and GHRP-6 pages; the wider class, including ipamorelin, is compared on our ipamorelin vs sermorelin page.
Sources and dates
- PubChem compound records CID 6918245 (pralmorelin) and CID 4345065 (GHRP-6), formula and weight, read 2026-10-03.
- KEGG DRUG D02040, pralmorelin dihydrochloride / pralmorelin hydrochloride (JAN), brand GHRP, read 2026-10-03.
- FDA. Certain bulk drug substances for use in compounding that may present significant safety risks: GHRP-2 and GHRP-6 entries (29 September 2023), content current as of 2026-04-22, read 2026-10-03.
- Bowers CY. GH releasing peptides — structure and kinetics. J Pediatr Endocrinol 1993;6(1):21–31 (PMID 8374685), abstract read 2026-10-03.
- Ghigo E et al. Growth hormone-releasing peptides. Eur J Endocrinol 1997;136(5):445–60 (PMID 9186261), abstract read 2026-10-03.
- Arvat E et al. Effects of GHRP-2 and hexarelin … on GH, prolactin, ACTH and cortisol levels in man. Peptides 1997;18(6):885–91 (PMID 9285939), abstract read 2026-10-03.
- Cabrales A et al. Eur J Pharm Sci 2013;48(1–2):40–6 (PMID 23099431) and Mericq V et al. 1998 (PMID 9661608), as read for this site's GHRP-6 and GHRP-2 pages (2026-09-20/21).
- PubMed E-utilities counts and ClinicalTrials.gov v2 API (GHRP-2, pralmorelin, GHRP-6, growth hormone releasing peptide-6), read 2026-10-03; openFDA adverse-event endpoint, "GHRP" (5 reports), read 2026-10-03.
Corrections go to the contact page.