The three growth hormone secretagogues most often compared, all acting through the ghrelin receptor, are ipamorelin, GHRP-2 and GHRP-6. What separates them is less the growth hormone pulse itself than the side effects. GHRP-6 produces the strongest hunger, GHRP-2 is regarded as the strongest by peak growth hormone concentration, and ipamorelin is the only one of the three that does not significantly raise cortisol, prolactin and ACTH.
This article sets those differences out as one map and adds a fourth molecule from the same family, hexarelin. The wider context of the group is covered in the pillar article on growth hormone peptides.
How do ipamorelin, GHRP-2 and GHRP-6 work?
All three stimulate the same receptor, the ghrelin receptor designated GHS-R1a, and produce a pulsatile release of growth hormone from the pituitary. GHRP-2 and GHRP-6 are hexapeptides, molecules of six amino acids. Ipamorelin is a pentapeptide, of five. The mechanism of growth hormone stimulation is similar across them, which is why they are compared mainly by their side effects.
They also belong to one family together with hexarelin and with ghrelin, the hormone produced in the stomach. None of them supplies growth hormone from outside. Each acts on the pituitary cell that produces it, which is why the effect is a pulse rather than a sustained elevation.
Which raises cortisol and prolactin?
GHRP-6, GHRP-2 and hexarelin raise cortisol and prolactin in a dose-dependent way above a certain threshold. Ipamorelin does not. It gives a negligible rise in cortisol even at very high doses and does not meaningfully raise ACTH or prolactin. That is the main reason it is called a selective or clean GHRP.
The basis for that distinction is a 1998 paper in the European Journal of Endocrinology. The authors showed that ipamorelin releases growth hormone with a potency comparable to GHRP-6 but does not raise ACTH or cortisol above the level seen after GHRH alone. A review of peptides affecting the growth hormone axis, published in 2026 in Frontiers in Endocrinology, lists raised prolactin and cortisol, appetite changes and disturbances of glucose metabolism among the reported side effects of the whole group.
Which increases appetite?
GHRP-6 acts most strongly here. It produces intense hunger, the strongest of all the peptides in this group, beginning 15 to 20 minutes after injection. GHRP-2 stimulates appetite moderately. Ipamorelin at standard doses gives minimal appetite stimulation.
That difference is an advantage or a drawback depending on the goal. When building mass, where the problem is eating enough calories, strong hunger helps. When reducing body fat, the same property gets in the way, and a milder molecule is chosen instead.
Which gives the strongest growth hormone pulse?
By peak growth hormone concentration, GHRP-2 is regarded as the strongest. GHRP-6 gives an amplitude per injection comparable to ipamorelin or higher. The differences in pulse strength are nevertheless smaller than the differences in side effect profile.
It is worth knowing where such rankings come from. They do not come from one study in which four molecules were given to the same group of people and compared. They come from assembling separate studies, run in different years, in different groups and at different doses. That is enough to set an order, but not to state a difference in percentages.
And hexarelin?
Hexarelin, also called examorelin, belongs to the same group and likewise raises cortisol and prolactin. A dose-response study in healthy adult men, published in December 1996 in the Journal of Clinical Endocrinology and Metabolism, showed rises in growth hormone, prolactin and cortisol, all three dose-dependent. Prolactin rose by around 180 percent, and the growth hormone response curve reached a plateau.
The most interesting result of that work concerns combination. Giving growth hormone releasing hormone together with a small dose of hexarelin produced a large growth hormone pulse with a moderate rise in prolactin and no rise in cortisol. The cortisol rise is therefore tied to the size of the hexarelin dose rather than being an inherent property of the molecule.
Hexarelin also has a second, separate route of action. A 2002 paper in Circulation Research showed that it binds CD36, a protein present in heart muscle cells and in the vascular endothelium. That work was done in animals and isolated hearts, so nothing follows from it about therapeutic action in humans.
Table: ipamorelin, GHRP-2, GHRP-6 and hexarelin
| Feature | Ipamorelin | GHRP-2 | GHRP-6 | Hexarelin |
|---|---|---|---|---|
| Structure | pentapeptide | hexapeptide | hexapeptide | hexapeptide |
| Rise in cortisol and prolactin | negligible | dose-dependent | dose-dependent | dose-dependent |
| Appetite stimulation | minimal | moderate | very strong | no comparison in the sources |
| Peak growth hormone | moderate | highest of the three | comparable to ipamorelin or higher | no direct comparison with GHRP-2 in humans |
| Status | unapproved, WADA S2 | unapproved, WADA S2 | unapproved, WADA S2 | unapproved, WADA S2.2.4 as examorelin |
What these comparisons do not tell you
They do not tell you how these molecules compare in humans after weeks of use. The comparisons in this article concern single administrations and hormonal responses measured in hours. There are no randomised trials comparing the effect of these peptides on body composition, strength or recovery in healthy adults.
Nor do they say anything about safety with long-term use. Side effect data come from short studies and from reports, not from observations over years. Any description promising a specific physique result from these peptides runs ahead of what has been measured.
What is the status of these peptides?
None of them is an approved medicine, and data on long-term safety in humans are limited. All are banned in sport on the World Anti-Doping Agency list in category S2, in and out of competition. Hexarelin appears there under the name examorelin, in section S2.2.4, in the same entry as GHRP-1 through GHRP-6 and ipamorelin.
In our shop they appear as research material: ipamorelin, GHRP-2, GHRP-6 and hexarelin. There are also ready-made combinations with a GHRH analogue in one vial, for example GHRP-2 & CJC-1295 and GHRP-6 & CJC-1295 MIX. The cart and the checkout are in English and prices are shown in Polish zloty.
Frequently asked questions
How does ipamorelin differ from GHRP-2 and GHRP-6?
Ipamorelin does not significantly raise cortisol, prolactin or ACTH and gives minimal hunger. GHRP-2 and GHRP-6 raise cortisol and prolactin in a dose-dependent way, and GHRP-6 additionally produces very strong appetite.
Which of these peptides increases appetite most?
GHRP-6. It produces intense hunger beginning 15 to 20 minutes after injection, the strongest in the group.
Which gives the strongest growth hormone pulse?
By peak growth hormone concentration, GHRP-2 is regarded as the strongest.
Is hexarelin stronger than GHRP-2?
No direct comparison of the strength of these two molecules in humans has been published. GHRP-2 is regarded as the strongest by peak growth hormone concentration, while hexarelin has its own dose-response study from 1996.
Are there comparative human trials?
There are no randomised trials comparing these peptides for body composition, strength or recovery. The available data concern the hormonal response after a single administration.
Are they allowed in sport?
They are not. All appear on the World Anti-Doping Agency list in category S2, and hexarelin under the name examorelin in section S2.2.4.
Where this information comes from
The comparison of cortisol, prolactin, appetite and peak growth hormone for ipamorelin, GHRP-2 and GHRP-6, along with the absence of approval and the status on the World Anti-Doping Agency list, comes from material published by Peptidepedia on 6 May 2026, checked on 31 August 2026.
The profile of ipamorelin comes from Raun K and co-authors, “Ipamorelin, the first selective growth hormone secretagogue”, European Journal of Endocrinology 1998, PMID 9849822. The hexarelin data come from a dose-response study in humans published in the Journal of Clinical Endocrinology and Metabolism in December 1996, PMID 8954038, and from a paper on CD36 binding in Circulation Research, 2002, PMID 11988484. The position of hexarelin on the prohibited list under the name examorelin comes from the World Anti-Doping Agency list for 2026, section S2.2.4. The list of reported side effects for the whole group comes from a review by Dominikowski A and co-authors in Frontiers in Endocrinology, 2026, PMID 42395176. The abstracts were read through Europe PMC, most recently on 7 September 2026.