Hexarelin vs Ipamorelin: Potency, Side Effects, Desensitization

Key takeaways

• Hexarelin and ipamorelin both activate the ghrelin receptor to release growth hormone (GH). Hexarelin is a six-amino-acid peptide from the 1990s GHRP family; ipamorelin is a five-amino-acid peptide Novo Nordisk designed to release GH without the other hormones.
• Potency: hexarelin probably releases more GH per dose, but the two have never been tested in the same study. Hexarelin is near its maximum at 1 to 2 mcg/kg intravenously; ipamorelin matched GHRP-6 in animals and has one human pharmacokinetic study, in 40 men.
• Side effects: hexarelin raises prolactin and cortisol in people and reduced deep sleep at night. Ipamorelin did not raise ACTH or cortisol in pigs even at more than 200 times the dose that gave half its maximal GH release, but that selectivity has never been confirmed in people.
• Desensitization: hexarelin's GH response fell by 45% over 16 weeks of twice-daily use and recovered within four weeks of stopping. Whether ipamorelin fades has never been measured in humans.
• Neither has shown a benefit for muscle, fat, sleep or recovery, and neither can be legally compounded in the US in October 2026. FDA's advisory committee voted 0 to 12 against ipamorelin in 2024 and it remains in Category 2 for outsourcing facilities; hexarelin has never been through FDA's compounding review at all.

The direct answer: hexarelin is the stronger GH releaser and the dirtier one; ipamorelin is the more selective one on paper, with almost no human data to confirm it. Neither has shown a result anyone would feel, and neither is legal to compound in the United States. Our hexarelin profile covers hexarelin's evidence and legal status in full, the hexarelin dosage article lists every studied dose, and the CJC-1295 and ipamorelin profile covers ipamorelin.

Side by side

Potency: what 'stronger' means here

Hexarelin's dose-response is well mapped. In healthy men given intravenous doses from 0 to 1 mcg/kg, the GH response reached a plateau at 1 mcg/kg, about 70 mcg for a 70 kg adult, with half the maximal effect at about 0.5 mcg/kg (Massoud 1996). That is a small amount of peptide for a large GH pulse, which is where hexarelin's reputation as the "strongest GHRP" comes from; the background of a 2004 sleep study described it as superior to GHRH and GHRP-6 in releasing GH (Frieboes 2004).

Ipamorelin's human picture is thinner. In the one pharmacokinetic study, 40 healthy men (eight per dose) received 15-minute infusions of 4.2 to 140 nmol/kg, roughly 3 to 100 mcg/kg; every dose produced a single GH pulse peaking at about 40 minutes, and the drug's half-life was about two hours (Gobburu 1999). The abstract reports a model of the response rather than peak GH by dose, so it cannot be laid against hexarelin's curve. In rats and pigs, ipamorelin released GH with a potency and maximum similar to GHRP-6 (Raun 1998).

Put together, the indirect evidence suggests hexarelin releases more GH per dose. It is indirect, it has never been tested head to head, and it measures the wrong thing for most buyers. A bigger GH pulse has not translated into a higher IGF-1 or a body-composition change for hexarelin in the one adult study long enough to look, as our hexarelin profile details.

Side effects: cortisol, prolactin and sleep

This is the real difference between the two, and the reason ipamorelin was developed.

Hexarelin raises other hormones. In healthy men, intravenous hexarelin raised prolactin by up to 180% and cortisol by about 40% from 0.5 mcg/kg upward (Massoud 1996). At night, four 50 mcg doses raised GH, prolactin, ACTH and cortisol and reduced the deepest stage of sleep compared with placebo (Frieboes 2004). With regular use the picture softens: after 16 weeks of twice-daily injections, the cortisol response to the morning dose was lower than at baseline, and ACTH, prolactin and 24-hour urinary cortisol did not change, so chronic overstimulation did not occur at that dose (Rahim 1999).

Ipamorelin was built to avoid them, in animals. In pigs, GHRP-6 and GHRP-2 raised ACTH and cortisol, while ipamorelin did not, even at more than 200 times the dose that gave half its maximal GH release, and none of the peptides tested affected prolactin, thyroid or reproductive hormones (Raun 1998). The human pharmacokinetic study reported GH only (Gobburu 1999), so the selectivity that makes ipamorelin attractive has never been confirmed in a person at the doses clinics sell.

Ipamorelin's clinical safety record is one trial. In 117 adults after bowel surgery, ipamorelin 0.03 mg/kg intravenously twice daily for up to seven days did not speed recovery (median time to a tolerated meal 25.3 versus 32.6 hours, p = 0.15); adverse events occurred in 87.5% on ipamorelin and 94.8% on placebo, and the authors judged it well tolerated (Beck 2014). FDA's Category 2 entry for ipamorelin notes that a published study identified serious adverse events, including a death, when ipamorelin was given intravenously for gastric motility, and that FDA lacks safety information for other injection routes (FDA Category 2 page). Neither statement shows the drug caused a death; both show how little safety data exists.

Desensitization

Hexarelin: documented, partial, reversible. In 12 healthy older adults on twice-daily injections, the GH response to a test dose, measured as the area under the GH curve, fell from 19.1 to 12.3 by week 4 and to 10.5 by week 16, a 45% drop, then returned to 19.4 four weeks after stopping (Rahim and Shalet 1998). The dosage article covers the children's data and the one-day studies in which a second or third injection already worked less well.

Ipamorelin: unmeasured in people. Its human data are the single-dose pharmacokinetic study and the seven-day surgical trial, which measured bowel recovery rather than GH (Gobburu 1999) (Beck 2014). Whether ipamorelin keeps its effect with nightly use is an open question, not an advantage. Sellers who claim it "does not desensitize" are reporting an absence of data.

Legal status

The routes differ but the destination is the same: no 503A pharmacy and no 503B outsourcing facility may legally make either one, and a prescription does not change that. Our legal tracker has the committee record for ipamorelin and the 2026 warning letters to research-peptide sellers; the hexarelin profile applies each 503A test to hexarelin.

What to do instead

If the goal is a monitored rise in GH, the secretagogue a licensed US pharmacy can dispense is sermorelin, a GHRH analog with human trials and an FDA approval history; our best HGH peptides ranking puts it alongside brand-only tesamorelin (Egrifta), which cannot be compounded. A reasonable prescription starts with a baseline IGF-1 and repeats it, which is more than either research vial offers. Our reconstitution calculator is for medications like that, dispensed with a labeled concentration, not for research vials.

Bottom line

Hexarelin versus ipamorelin is a choice between a stronger GH releaser that brings cortisol, prolactin and shallower sleep with it and loses part of its effect within weeks, and a cleaner one whose cleanliness has been shown in pigs and whose human record is one pharmacokinetic study and one failed surgical trial. Neither has shown a benefit for muscle, fat, recovery or aging, and neither can be legally compounded in the United States. The honest comparison ends with neither.

Frequently asked questions

+−Is hexarelin stronger than ipamorelin?

Probably, per dose, but no study has compared them in the same people. Hexarelin produces close to its maximum growth hormone pulse at 1 to 2 mcg per kilogram intravenously and is described in the research literature as stronger than GHRP-6. Ipamorelin matched GHRP-6 in rats and pigs, and its one human study reported a model of the response rather than peak levels. Strength is also the wrong question: hexarelin's extra growth hormone comes with cortisol and prolactin.

+−Which has fewer side effects, hexarelin or ipamorelin?

On the hormones, ipamorelin probably does. Hexarelin raises prolactin and cortisol in people from moderate intravenous doses upward, and reduced deep sleep at night. Ipamorelin did not raise ACTH or cortisol in pigs even at very high doses, but nobody has measured cortisol or prolactin in people taking it at clinic doses. Neither has long-term safety data, and research vials of either carry unknown content.

+−Does ipamorelin cause desensitization like hexarelin?

Nobody knows in humans. Hexarelin's fade is documented: on twice-daily injections the growth hormone response was 45 percent lower at 16 weeks and recovered four weeks after stopping. Ipamorelin's human data are one single-dose study and a 7-day intravenous trial after bowel surgery that measured recovery, not growth hormone, so whether it fades with regular use has not been measured in people.

+−Can you stack hexarelin and ipamorelin?

No study has tested the combination. Both act on the same ghrelin receptor, so stacking them adds exposure without adding a new mechanism, and hexarelin's cortisol and prolactin effects would still come along. Neither can be legally compounded in the United States, so a stack means two unverified research vials.

+−Is ipamorelin or hexarelin better for sleep?

Neither has evidence of improving sleep. In the only sleep study of either, four 50 mcg doses of hexarelin at night reduced the deepest stage of sleep and raised cortisol and ACTH. No study has recorded sleep in anyone taking ipamorelin.

+−Are hexarelin and ipamorelin legal?

Neither can be legally compounded or sold for human use in the United States in October 2026. Ipamorelin was placed in FDA's Category 2 in 2023, FDA's advisory committee voted against it in October 2024 (0 yes, 12 no, 1 abstention), and it remains in Category 2 for outsourcing facilities. Hexarelin is not on any of FDA's compounding lists at all, because it has never been through FDA's review.

+−Which is better for muscle growth, hexarelin or ipamorelin?

Neither has shown it. The only adult study of regular hexarelin use found no change in lean mass, fat or IGF-1 after 16 weeks of twice-daily injections in older adults. Ipamorelin has never been studied for body composition in people. Raising growth hormone for a few hours is a mechanism, not a muscle result.

Sources

1. StudyMassoud AF, Hindmarsh PC, Brook CG. Hexarelin-induced growth hormone, cortisol, and prolactin release: a dose-response study. J Clin Endocrinol Metab 1996;81:4338-41. (1996)
2. StudyRahim A, Shalet SM. Does desensitization to hexarelin occur? Growth Horm IGF Res 1998;8 Suppl B:141-3. (1998)
3. StudyRahim A, O'Neill PA, Shalet SM. The effect of chronic hexarelin administration on the pituitary-adrenal axis and prolactin. Clin Endocrinol (Oxf) 1999;50:77-84. (1999)
4. StudyFrieboes RM et al. Hexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers. Psychoneuroendocrinology 2004;29:851-60. (2004)
5. StudyRaun K et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol 1998;139:552-61. (1998)
6. StudyGobburu JV et al. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res 1999;16:1412-6. (1999)
7. StudyBeck DE, Sweeney WB, McCarter MD; Ipamorelin 201 Study Group. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis 2014;29:1527-34. (2014)
8. RegulatoryFDA. Certain bulk drug substances for use in compounding may present significant safety risks (Category 2 list and nominated-but-withdrawn substances; content current as of April 22, 2026). (2026)