Ipamorelin compared with GHRP-2, GHRP-6 and hexarelin

Published August 28, 2026 · Artemis Labs

Ipamorelin, GHRP-2, GHRP-6 and hexarelin all act at the same receptor — the one ghrelin binds — and all four release growth hormone in published animal research. The comparison that separates them is not potency. In the 1998 study that tested them side by side in conscious swine, ipamorelin and GHRP-6 released growth hormone at similar doses, and GHRP-2 was more potent with a lower maximum. What differed was everything else the compounds moved: GHRP-6 and GHRP-2 raised ACTH and cortisol, and ipamorelin did not. All four appear together in anti-doping method papers, because laboratories screen for the class rather than for one member.

Key findings

• Head-to-head in conscious swine: ipamorelin “ED50 = 2.3+/-0.03 nmol/kg”, GHRP-6 “ED50 = 3.9+/-1.4 nmol/kg”, GHRP-2 “ED50 = 0.6 nmol/kg and Emax = 56+/-6 ng GH/ml plasma” (PMID 9849822).
• The dividing line, verbatim from the same study: “Administration of both GHRP-6 and GHRP-2 resulted in increased plasma levels of ACTH and cortisol.”
• Ipamorelin clears differently: in rats it showed “a systemic plasma clearance 5-fold lower than that of GHRP-6,” and was excreted mainly in urine while GHRP-6 went predominantly into bile (PMID 9879640).
• Anamorelin, a later compound in the class, differs in a way that matters: in ferrets it produced central effects that ipamorelin did not, which the authors attributed to brain penetration (PMID 39043357).

What the four compounds share

All four are short synthetic peptides that bind GHS-R1a, the receptor for ghrelin. Activating it causes pituitary cells to release stored growth hormone. All four contain unnatural D-form amino acids, which is what keeps them intact long enough to reach the receptor — a 2014 method paper describes the family as “synthetic met-enkephalin analogues that include unnatural D-amino acids.”

They also share a research context. A large fraction of the published work on all four comes from anti-doping laboratories developing detection methods, and those papers routinely list them together as a screening panel.

How they differ in the published comparisons

Hormone selectivity. This is the substantive difference and it comes from one carefully built experiment. In swine, none of the tested compounds moved FSH, LH, prolactin or TSH. But GHRP-6 and GHRP-2 raised ACTH and cortisol, while ipamorelin’s ACTH and cortisol levels were not significantly different from those seen after the body’s own releasing hormone — a result that held at doses more than two hundred times the half-maximal growth hormone dose. Our page on the selectivity research goes through that study in detail, including its limits.

Potency and maximum effect. These are not the same thing, and the swine data separates them neatly. GHRP-2 needed the smallest dose but produced the lowest peak. Ipamorelin and GHRP-6 needed larger doses and reached higher peaks. A compound can be more potent and less effective at once.

Disposition. The 1998 pharmacokinetic comparison in rats found ipamorelin behaved unlike the rest: five-fold lower plasma clearance than GHRP-6, and a different excretion route. The same study measured how well each crossed the nasal lining in rats, finding ipamorelin lower than several of the others — a laboratory measurement of membrane transport, not a suggestion about how anything should be handled.

Receptor breadth. Hexarelin is described in the wider literature as interacting with CD36 in addition to the ghrelin receptor. We have not verified that in a primary source here, so we note it as a claim to check rather than a fact to rely on.

Where anamorelin fits

Anamorelin is a newer compound at the same receptor, and the cleanest published comparison against ipamorelin is a 2024 ferret study of cisplatin chemotherapy. Given into the abdomen, both compounds reduced delayed-phase weight loss “by approximately 24 %”. Neither affected vomiting by that route. But anamorelin given directly into the brain’s ventricles reduced acute emesis by 60%, and the authors concluded that “brain penetration is important for its anti-emetic mechanism of action.”

Ipamorelin produced no equivalent central effect. That is a real mechanistic distinction between two compounds at the same receptor, and it is the sort of result that only shows up when someone tests the same question by two different routes.

What the research does not show

None of these comparisons involved humans. The selectivity work is in swine, rats and cultured pituitary cells; the disposition comparison is in rats; the anamorelin contrast is in ferrets. No head-to-head human study of any two of these compounds appears in the record we retrieved.

Nothing here shows that any of the four is safer than another. Measuring which hormones move is not measuring harm, and no study in this comparison was designed to compare adverse effects.

And a finding that complicates the whole family: in mice, growth hormone secretagogues raised body fat through a mechanism independent of growth hormone, which the authors suggested “may include increased feeding” (PMID 11162489). Selectivity among pituitary hormones did not translate into a narrow effect on the animal.

Frequently asked questions

Is ipamorelin stronger than GHRP-6?

No. In the swine comparison the two were close on both dose and maximum effect. The published difference is in the other hormones, not in growth hormone.

Why do these compounds appear together in so many papers?

Because anti-doping laboratories screen for the class. A single method paper commonly covers GHRP-1 through GHRP-6, hexarelin, alexamorelin and ipamorelin at once.

Are these compounds prohibited in sport?

Published doping-control method papers name ipamorelin among the peptides covered by the World Anti-Doping Agency’s prohibited-substances list (PMID 26578461). We report what those papers say and do not restate the current list ourselves; anyone who needs the present status should read the list directly.

What about the GHRH-family peptides?

Different receptor entirely — CJC-1295, sermorelin and tesamorelin act on the growth hormone-releasing hormone receptor. Our guide to growth hormone research peptides covers both families.

References

1. Raun K, et al. Eur J Endocrinol. 1998. PMID 9849822.
2. Johansen PB, Hansen KT, Andersen JV, Johansen NL. Xenobiotica. 1998. PMID 9879640.
3. Lu Z, et al. Physiol Behav. 2024. PMID 39043357. DOI 10.1016/j.physbeh.2024.114644.
4. Thomas A, et al. J Sep Sci. 2016. PMID 26578461.
5. Timms M, et al. Drug Test Anal. 2014. PMID 24574167.
6. Lall S, et al. Biochem Biophys Res Commun. 2001. PMID 11162489.

Methodology: comparisons on this page are drawn only from studies that tested the compounds against each other in the same experiment. Values are quoted as published, with species named.

All compounds sold by Artemis Labs are for laboratory research use only. Nothing on this page is medical advice, and no statement has been evaluated by the FDA.