In the study that introduced ipamorelin, it released growth hormone without raising ACTH or cortisol above baseline even at more than 200 times its GH-releasing dose, while GHRP-6 raised both. That selectivity is the reason clinicians moved on from GHRP-6.
Ipamorelin and GHRP-6 are both growth hormone secretagogues. Each one binds the ghrelin receptor and triggers a GH pulse, which is a separate pathway from the GHRH receptor that sermorelin acts on. The difference that matters clinically is selectivity. GHRP-6 is the older hexapeptide, and it raises cortisol and ACTH along with GH [1]. Ipamorelin was designed to drop those off-target effects, and in the foundational study it released GH without significantly raising either [1]. GHRP-6 today exists only as a research chemical. Ipamorelin is the secretagogue prescribers actually reach for.
- Both act on the ghrelin receptor, distinct from the GHRH receptor sermorelin uses
- GHRP-6 raises cortisol and ACTH; ipamorelin did not, at more than 200 times its GH-releasing dose [1]
- The selectivity data for ipamorelin comes from swine and rats, not humans [1]
- Ipamorelin's only published efficacy trial missed its primary endpoint [3]
- Neither is an FDA-approved drug, and both are prohibited in tested sport [4][5][6]
Same Receptor, Different Selectivity
GHRP-6 was one of the first growth hormone releasing peptides developed, a synthetic hexapeptide that mimics ghrelin at the growth hormone secretagogue receptor. It is a potent releaser of GH. In humans, GHRH combined with GHRP-6 produced a GH response far larger than either alone, with GH area under the curve of 686 for GHRH, 1787 for GHRP-6, and 4111 for the combination, higher than the arithmetic sum of the two [2]. On raw GH release, GHRP-6 works.
The problem was never potency. It was everything else the molecule does at the same time. Because the ghrelin receptor also sits on the pathways that drive hunger and the stress axis, GHRP-6 does not stay in its lane.
Where GHRP-6 Falls Short
GHRP-6 raises cortisol and ACTH. In the study that introduced ipamorelin, both GHRP-6 and GHRP-2 released ACTH and cortisol, while ipamorelin did not do so at levels significantly different from GHRH stimulation [1]. A GH secretagogue that also nudges the stress hormones is working against part of what patients want from it.
GHRP-6 is also a strong appetite stimulant. Activating the ghrelin receptor is the mechanism by which ghrelin itself signals hunger, and marked appetite stimulation is the effect GHRP-6 is best known for outside of GH release. For a patient using a GH-axis peptide to improve body composition, a built-in hunger signal is a liability, not a feature.
- Raises cortisol and ACTH, unlike ipamorelin [1]
- Strong appetite stimulation through ghrelin-receptor agonism
- No selective advantage over newer secretagogues
- Never developed into an approved drug product
What Ipamorelin Improved On
Ipamorelin was introduced as the first selective growth hormone secretagogue [1]. The selling point is exactly the contrast above: comparable GH release without the cortisol and ACTH rise that GHRP-6 produces. That is why it displaced the older GHRPs in clinical peptide practice.
Two qualifications keep this honest. First, the selectivity data was generated in swine and rats, so the cortisol claim rests on animal work rather than human trials [1]. Second, ipamorelin's own clinical development did not target body composition. Its only published efficacy trial studied postoperative ileus and found a median time to first tolerated meal of 25.3 hours versus 32.6 hours on placebo, which did not reach statistical significance [3]. Development was discontinued afterward.
| Property | GHRP-6 | Ipamorelin |
|---|---|---|
| Peptide class | First-generation GHRP (hexapeptide) | Selective GH secretagogue |
| Receptor | Ghrelin receptor | Ghrelin receptor |
| Cortisol and ACTH | Raised in the comparison study [1] | Not significantly raised [1] |
| Appetite effect | Strong stimulation | Comparatively mild |
| Human selectivity data | Older, non-selective profile | Selectivity shown in swine [1] |
| FDA-approved product | None | None, in any form [5] |
| WADA status | Prohibited, S2.2.4 [6] | Prohibited, S2.2.4 [6] |
Regulatory Reality for Both
Neither peptide is an approved drug, and this is where class-shopping runs into a wall. There are no FDA-approved products containing ipamorelin in any form, and FDA lists ipamorelin acetate among bulk drug substances for use in compounding that may present significant safety risks [5]. In October 2024, FDA's Pharmacy Compounding Advisory Committee voted 0 in favor and 12 against placing ipamorelin on the 503A bulks list [4], citing a lack of data supporting safety and efficacy.
GHRP-6 has even less standing. It was never approved as a drug and is sold only as a research chemical, which means no pharmacy-grade sourcing, no compounding oversight, and no purity guarantee. Both peptides are named on the 2026 WADA Prohibited List under section S2.2.4, growth hormone secretagogues [6], prohibited at all times in tested sport.
The debate over which GHRP is best skips the harder question. Neither is an approved medicine, and one of them is a research chemical with no quality controls at all. The GH axis can be stimulated through a prescribable, monitored route instead.
The Prescribable Way to Touch the GH Axis
If the goal is a supported GH pulse rather than a peptide-forum experiment, the practical route is a GHRH analog under a prescriber. Sermorelin is a GHRH(1-29) analog that stimulates the same pituitary output, is dispensed through 503A or 503B compounding pharmacies, and is prescribed against a baseline IGF-1 with a 90-day retest to judge response.
That structure is the actual difference between the two approaches. A monitored GHRH-analog protocol gives you a lab number to titrate against. A research-chemical GHRP gives you neither a prescriber nor a way to know what is in the vial.
Most peptide sourcing skips the one thing that makes GH-axis therapy legible: a baseline IGF-1. SystemLabs includes baseline IGF-1 testing before prescribing sermorelin, so you start with a real number and can measure the 90-day response instead of guessing.
Bottom Line
Frequently Asked Questions
Is ipamorelin better than GHRP-6?
On side-effect profile, yes. Ipamorelin releases growth hormone without significantly raising cortisol or ACTH, while GHRP-6 raises both, and GHRP-6 also stimulates appetite strongly [1]. That selectivity is why ipamorelin replaced GHRP-6 in clinical peptide practice. Neither is an FDA-approved drug, so the comparison is between two unapproved options rather than two medicines.
Does GHRP-6 raise cortisol?
Yes. In the study that introduced ipamorelin, GHRP-6 and GHRP-2 both released ACTH and cortisol, while ipamorelin did not do so at levels significantly different from GHRH stimulation, even at more than 200 times its GH-releasing dose [1]. Raising the stress hormones alongside GH is the main reason GHRP-6 fell out of favor.
Why does GHRP-6 make you hungry?
GHRP-6 activates the ghrelin receptor, which is the same receptor ghrelin uses to signal hunger. Strong appetite stimulation is the effect GHRP-6 is best known for outside of GH release. For anyone using a GH-axis peptide to improve body composition, that built-in hunger signal works against the goal.
Is GHRP-6 legal or FDA approved?
GHRP-6 is not an FDA-approved drug and was never developed into an approved product. It is sold only as a research chemical, which means no pharmacy-grade sourcing or compounding oversight. It is also named on the 2026 WADA Prohibited List under growth hormone secretagogues and is banned at all times in tested sport [6].
Is ipamorelin FDA approved?
No. There are no FDA-approved products containing ipamorelin in any form, and FDA lists ipamorelin acetate among bulk substances for compounding that may present significant safety risks [5]. An FDA advisory committee voted 0 to 12 against permitting it for compounding in October 2024 [4]. Its only published efficacy trial, in postoperative ileus, missed its primary endpoint [3].
What can I use instead of GHRP-6 or ipamorelin?
For a monitored GH-axis protocol, sermorelin is the prescribable route. It is a GHRH(1-29) analog that stimulates the same pituitary GH output, is dispensed through 503A or 503B compounding pharmacies, and is prescribed against a baseline IGF-1 with a 90-day retest. That gives you a lab number to titrate against, which a research-chemical GHRP does not.
References
- Ipamorelin, the first selective growth hormone secretagogue European Journal of Endocrinology, 1998. PMID: 9849822. https://pubmed.ncbi.nlm.nih.gov/9849822/
- Growth hormone (GH) secretion in active acromegaly after the combined administration of GH-releasing hormone and GH-releasing peptide-6 Journal of Clinical Endocrinology & Metabolism, 1994. PMID: 8045963. https://pubmed.ncbi.nlm.nih.gov/8045963/
- Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients International Journal of Colorectal Disease, 2014. PMID: 25331030. https://pubmed.ncbi.nlm.nih.gov/25331030/
- Summary minutes of the Pharmacy Compounding Advisory Committee meeting, October 29, 2024 FDA Advisory Committee, 2024. PCAC summary minutes. https://www.fda.gov/media/185412/download
- Certain bulk drug substances for use in compounding that may present significant safety risks FDA.gov, Human Drug Compounding, 2026. Content current as of 04/22/2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- The 2026 Prohibited List: International Standard, section S2.2.4 growth hormone releasing factors World Anti-Doping Agency, 2026. WADA 2026 Prohibited List. https://www.wada-ama.org/en/resources/2026-prohibited-list
