GHRP 2 vs ipamorelin comes down to selectivity. Both peptides activate the ghrelin receptor and make the pituitary release growth hormone, but in the key animal study GHRP-2 also raised the stress hormones ACTH and cortisol, while ipamorelin did not.[1] GHRP-2 has far more human research and an approved diagnostic use in Japan; ipamorelin has one human dosing study and one failed surgery trial.[4][3][8]
This guide compares their potency, hormone side effects, hunger, half-life, human evidence, safety and legal status. For background, see our GHRP-2 and ipamorelin profiles and the growth hormone peptides hub.
At a glance
| GHRP-2 (pralmorelin) | Ipamorelin | |
|---|---|---|
| Size | 6 amino acids[4] | 5 amino acids[1] |
| Growth hormone potency in pigs | Higher (smaller dose needed)[1] | Lower, with a slightly higher peak[1] |
| ACTH and cortisol | Raised in pigs and people[1][2] | Not raised in pigs; not measured in people[1][3] |
| Hunger in people | Food intake up about 34% to 36%[5][6] | No human study; more eating and fat in mice[7] |
| Half-life (IV) | About 0.42 to 0.69 hours[4] | About 2 hours[3] |
| Approved anywhere | Japan, diagnostic test only[4] | No |
| FDA 503B safety-risk list | Yes (injectable and nasal), since 2023[11] | Yes, since 2023[11] |
How they work
Both are synthetic growth hormone secretagogues: they act at the receptor for ghrelin, the hunger hormone (also called the growth hormone secretagogue receptor), which triggers a pulse of growth hormone from the pituitary.[1][4] Novo Nordisk scientists derived ipamorelin from the structure of an older peptide, GHRP-1, and in 1998 called it the first “selective” member of the family.[1]
Neither peptide is the same as GHRH-type peptides such as sermorelin, tesamorelin or CJC-1295, which act on a different receptor. That is why ipamorelin is often paired with one of them; see our guides to CJC-1295 and ipamorelin and sermorelin vs ipamorelin.
Growth hormone potency
The only study that tested both side by side was the Novo Nordisk paper, in animals:[1]
- In conscious pigs, GHRP-2 needed a smaller dose to reach half its maximum effect (about 0.6 nmol/kg versus 2.3 nmol/kg for ipamorelin), so it was more potent.
- But its ceiling was lower: the maximum growth hormone level was about 56 ng/mL with GHRP-2 versus 65 ng/mL with ipamorelin.
In people, they have never been compared directly. GHRP-2 at 1 mcg/kg IV produced a strong response in healthy young adults, larger than GHRH.[2] Ipamorelin, given as 15-minute IV infusions to healthy men, caused a single burst of growth hormone that peaked about 40 minutes later.[3]
Cortisol, ACTH and prolactin: the selectivity question
This is the main reason people compare the two.
- GHRP-2: in pigs, it raised ACTH and cortisol.[1] In six healthy young adults in Turin, single IV doses raised prolactin, ACTH and cortisol, and the ACTH and cortisol rise was similar to that from the stress hormone CRH.[2]
- Ipamorelin: in pigs, it did not raise ACTH or cortisol beyond what GHRH caused, even at doses more than 200 times higher than needed to release growth hormone.[1]
- Prolactin and other hormones in pigs: none of the peptides tested, including GHRP-2 and ipamorelin, changed prolactin, LH, FSH or TSH.[1]
The catch is that ipamorelin’s selectivity has only been shown in animals. Its human study measured growth hormone, not cortisol or prolactin.[3]
Hunger and weight
- GHRP-2 is one of the few peptides in its class shown to increase eating in controlled human studies. Seven healthy men ate 35.9% more at a buffet during an infusion than on saline, and lean and obese adults ate about 34% more at the higher dose.[5][6]
- Ipamorelin has no human hunger study. In mice, two weeks of twice-daily injections increased food intake and body fat, an effect that did not depend on growth hormone.[7]
No controlled human trial has shown fat loss with either peptide.[15]
Human evidence
GHRP-2 has been tested in many small human studies. Its strongest evidence is diagnostic: in 77 healthy adults and 58 adults with severe growth hormone deficiency, a single 100 mcg IV dose clearly separated the two groups, which led to its approval as a test in Japan.[10][4] Daily injections lose some effect: in 9 healthy men given 100 mcg under the skin for 5 days, the growth hormone peak fell from 83 to 51 micrograms per liter.[14]
Ipamorelin has one published human dosing study, in healthy men given single IV infusions, and one published efficacy trial. In that phase 2 trial, 114 patients recovering from bowel surgery got 0.03 mg/kg by IV twice daily; it did not significantly shorten the time to a tolerated meal compared with placebo.[3][8]
For the doses each one used, see our GHRP-2 dosage and ipamorelin dosage guides.
Side effects compared
| GHRP-2 | Ipamorelin | |
|---|---|---|
| Main human safety source | Japan’s label (single diagnostic dose)[4] | One phase 2 surgery trial (IV)[9] |
| Most common reported effects | Feeling of warmth (16.0%), stomach rumbling, sweating, thirst, hunger, drowsiness, nausea[4] | Low potassium (12.5% vs 3.4%), insomnia (10.7% vs 5.2%), high blood sugar at discharge (14.3% vs 8.6%)[9] |
| Serious concerns raised by FDA | Increased insulin needs, deaths of critically ill subjects, infection, pancreatitis; causality not established[11] | Two deaths after surgical complications; unclear if related[9] |
Both carry FDA’s warning about possible immune reactions from clumped peptide or impurities, and both contain unnatural amino acids that make products harder to test.[11] A 2026 endocrine review listed prolactin and cortisol rises, appetite changes, abnormal blood sugar, fluid retention and joint aches among the effects clinicians see with this class.[15] More detail is in our GHRP-2 side effects and ipamorelin side effects guides.
Legal status
- Approval: GHRP-2 is approved only in Japan, as a diagnostic test.[4] Ipamorelin is not approved anywhere, and FDA found no human data for it given under the skin.[9]
- Outsourcing facilities (503B): FDA placed ipamorelin acetate and injectable or nasal GHRP-2 in its significant-safety-risk category on September 29, 2023.[11]
- Traditional pharmacies (503A): GHRP-2 is in the category for substances nominated without adequate support on FDA’s May 2026 list.[12] For ipamorelin, FDA’s advisory committee voted 0 to 12, with one abstention, against adding it in October 2024.[13]
For how these rules work, see 503A vs 503B compounding.
Which is “better”?
Neither has shown a clinical benefit for muscle, fat loss, sleep or aging in a controlled human trial.[15] On the evidence available:
- GHRP-2 has more human data and a known side-effect profile, including hunger and stress-hormone rises.
- Ipamorelin is likely more selective, but that is based on animal data, and its human safety data come from hospital patients given IV doses.
For related comparisons, see GHRP-2 vs GHRP-6 vs hexarelin and hexarelin vs ipamorelin.
Questions to ask a clinician
- Which human study supports using this peptide for my goal?
- Will you check my cortisol, prolactin, blood sugar and IGF-1?
- How will we know if it is working, and when would we stop?
- Is there an FDA-approved treatment for my condition instead?
This is general information, not medical or legal advice.
