GHRP-2 vs GHRP-6 vs hexarelin is a comparison of three closely related peptides that all make the pituitary gland release growth hormone by activating the ghrelin receptor. GHRP-6 came first, in 1984; GHRP-2 and hexarelin were later built as more potent versions.[2][5][1] The only head-to-head human study we found compared two of them: GHRP-2 against hexarelin, in Turin.[1]
This guide compares their growth hormone effect, hunger, cortisol and prolactin, how quickly they lose effect, approvals and legal status, then sets them against ipamorelin and the pill MK-677. For background on the whole family, see our growth hormone peptides hub.
At a glance
| GHRP-6 | GHRP-2 | Hexarelin | |
|---|---|---|---|
| First described | 1984, Tulane University[2][3] | After GHRP-6[5]; approved in Japan 2004[8] | After GHRP-6; human studies by 1994[4][6] |
| Growth hormone release | Strong; synergistic with GHRH[3] | Strong; similar to hexarelin[1] | Strong; about 2x GHRH[4] |
| Hunger in people | No controlled study found; eating in rats[11] | Food intake up about 36%[9] | Not measured in studies we found |
| Cortisol and prolactin | About doubled at 1 mcg/kg[3] | Raised, similar to hexarelin[1] | Prolactin up to 180%, cortisol about 40%[12] |
| Loss of effect with daily use | No long-term study found | Acute response held over months (nasal, children)[16] | About 45% drop over 16 weeks[13] |
| Half-life of the drug (IV) | About 2.5 hours[19] | About 33 minutes (children)[20] | Not reported in human studies we found |
| Approved anywhere | None found | Japan, diagnostic test only[8][32] | None found |
| FDA compounding status | 503B safety risk; 503A category 3[23][24] | 503B safety risk (injected, nasal); 503A category 3[23][24] | Not on any FDA list[24][25] |
| Banned by WADA | Yes[27] | Yes[27] | Yes, as examorelin[27] |
Growth hormone potency: the head-to-head evidence
The only direct human comparison among the three that we found comes from the University of Turin. In six healthy young adults, 1 mcg/kg IV of GHRP-2 or hexarelin produced a similar, strong growth hormone response, larger than GHRH. Doubling the dose to 2 mcg/kg raised it further, again equally for both.[1]
GHRP-6 has no matching head-to-head study that we found. On its own, in 18 healthy men, 1 mcg/kg IV pushed average peak growth hormone to 68.7 micrograms per liter.[3] Hexarelin was made from GHRP-6 by modifying one amino acid, producing a version active by mouth, though oral absorption rarely exceeded 1%.[6] The Turin researchers described GHRP-2 and hexarelin as potent “super-analogs” of GHRP-6, but no study we found has measured GHRP-6 against either at matched doses in people.[1]
In practice, all three are strong releasers when injected. The class acts synergistically with GHRH, which is why GHRH plus GHRP-6 became a diagnostic test for growth hormone deficiency.[5][21]
Hunger and appetite
Hunger is where these peptides are said to differ most, but the evidence is lopsided:
- GHRP-2: in New York, seven healthy men ate 35.9% more at a buffet during a GHRP-2 infusion than on saline.[9] A follow-up in lean and obese adults found a dose-related rise of 10% to 34%.[10] In Chile, 7 of 10 children taking GHRP-2 by mouth reported more appetite in the first 6 months.[29]
- GHRP-6: injected into rats’ brains, it triggered eating independently of growth hormone.[11] We found no controlled human feeding study.
- Hexarelin: we found no human study measuring hunger or food intake.
The popular idea that GHRP-2 does not cause hunger is not supported: it is one of the few GHRPs shown in controlled studies to increase eating in people.[9][10]
Cortisol and prolactin
None of the three is selective for growth hormone. In the Turin study, GHRP-2 and hexarelin raised prolactin, ACTH and cortisol to a similar degree; their effect on ACTH and cortisol matched that of the stress hormone CRH.[1] GHRP-6 roughly doubled prolactin and cortisol at 1 mcg/kg but not at lower doses.[3] For hexarelin, prolactin rose by up to 180% and cortisol by about 40% at higher doses, while a low dose paired with GHRH avoided the cortisol rise.[12]
These are short-lived rises after single doses. Over 16 weeks of twice-daily hexarelin, the cortisol response actually shrank and prolactin did not climb further.[14]
Desensitization: do they stop working?
Partial loss of effect is a known feature of the whole class, more with continuous infusion than with separate doses.[5]
- Hexarelin has the clearest data. In 12 healthy older adults, the growth hormone response fell about 45% over 16 weeks of twice-daily injections, then recovered 4 weeks after stopping.[13] In short children using a nasal spray, it roughly halved within a week, though growth speed still rose.[15]
- GHRP-2: in 15 children using a nasal spray for 6 to 24 months, the acute growth hormone response to a test dose did not change significantly.[16]
- GHRP-6: we found no long-term human study.
How they compare with ipamorelin and MK-677
| Ipamorelin | MK-677 | |
|---|---|---|
| Form | Injected peptide[17] | Daily pill[18] |
| Cortisol | No rise in pigs, even at high doses[17] | Up about 47 nmol/L over a year[18] |
| Hunger | No human hunger study found | Increased appetite that faded within months[18] |
| Key human trial | Up to 7 days after bowel surgery; no benefit over placebo[31] | 2 years in older adults[18] |
| FDA compounding status | 503B safety risk; advisers voted against 503A[23][26] | Safety risk under 503A and 503B[23] |
Ipamorelin is the more selective member of the family: in pigs it matched GHRP-6 for growth hormone release, while GHRP-6 and GHRP-2 raised ACTH and cortisol and ipamorelin did not.[17] MK-677 acts on the same receptor but is taken by mouth once daily. In a 2-year trial in 65 older adults, it raised growth hormone and IGF-1 to young-adult levels and added about 1.1 kg of fat-free mass over the first year, but raised fasting blood sugar and reduced insulin sensitivity.[18]
People often combine these with a GHRH-type peptide; see our guides to CJC-1295 + ipamorelin and tesamorelin + ipamorelin.
Approvals and legal status
- GHRP-2 is the only one of the three with an approved use: Japan approved pralmorelin in October 2004, from Kaken Pharmaceutical, as a single IV test for growth hormone deficiency.[8][32] A Japanese validation study in 135 people backed a clear cut-off for diagnosis.[7]
- FDA, outsourcing facilities (503B): GHRP-6 and injectable or nasal GHRP-2 have been in category 2, substances that may present significant safety risks, since September 29, 2023.[23] FDA’s March 2025 503B list keeps GHRP-2 for other routes in category 1, under evaluation.[25]
- FDA, traditional pharmacies (503A): both GHRP-2 and GHRP-6 sit in category 3, nominated without adequate support, on FDA’s May 2026 list.[24]
- Hexarelin is absent from FDA’s 503A, 503B and safety-risk lists.[23][24][25]
- Advisory committee: none of the three was reviewed at FDA’s October 2024 compounding advisory meeting.[26]
- Sport: WADA names all three, prohibited at all times.[27]
Side effects compared
FDA’s safety concerns differ by compound. For GHRP-6, it cites a potential effect on cortisol and higher blood sugar from reduced insulin sensitivity. For GHRP-2, it cites reports of increased insulin needs, deaths of critically ill study subjects, infection and pancreatitis, while noting causality has not been established. It also warns both may trigger immune reactions from clumped peptide or impurities.[23] Hexarelin has no FDA safety review; its human studies mainly report hormone changes, and single IV doses acutely increased heart pumping in bypass patients.[22]
All three raise cortisol and prolactin after single doses, and GHRP-2 is shown to raise hunger in people. A 2026 review notes that robust long-term safety data are lacking for this class.[28]
Dosing: what studies used
Human studies mostly used single IV doses of up to 1 mcg/kg for GHRP-6 and 1 to 2 mcg/kg for GHRP-2 and hexarelin.[1][3] Japan’s diagnostic dose of GHRP-2 is 100 mcg IV once in adults.[32] No dose of any of the three has been shown to build muscle or reduce fat in a controlled trial.[28] For converting milligrams to syringe units, see our peptide calculator.
What users report
The bottom line
In the only head-to-head human study we found, GHRP-2 and hexarelin were equally potent and equally prone to raising stress hormones; GHRP-6, the original, has never been compared directly with either in people, and we found no controlled trial showing real-world benefits for any of them. GHRP-2 stands apart for its approved diagnostic role in Japan and controlled evidence of raising appetite; hexarelin for its heart research and clearest evidence of fading effect. More compounds are on our growth hormone peptides page.
This is general information, not medical or legal advice.
