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Hexarelin vs Ipamorelin

Last updated: October 3, 2026 · 6 min read · By the Grey Peptides Editorial Board

Scientist in a lab coat handling test tubes under pink lighting, using a microscope
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Grey Peptides
Grey Peptides Editorial Board
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Key takeaways
  • Both release growth hormone through the ghrelin receptor. Hexarelin is a GHRP-6 derivative with many small human studies from the 1990s; ipamorelin was developed to release growth hormone without raising stress hormones.
  • Hexarelin's response fades with regular use: over 16 weeks of twice-daily injections the growth hormone response fell by about half, then recovered four weeks after stopping.
  • Neither is approved, neither has long-term safety data, and both are prohibited in sport.

Side by side

Hexarelin Medium and ipamorelin Medium are growth hormone-releasing peptides, which act on the receptor the stomach hormone ghrelin uses rather than on the GHRH receptor. Hexarelin was made by swapping GHRP-6's tryptophan for a more stable 2-methyl-tryptophan, giving a peptide that released growth hormone as effectively as GHRP-6 in rats 1. Ipamorelin came later, designed as a more selective member of the family 2. WADA's 2026 List names both among the growth hormone secretagogues 3. The table is read from our encyclopedia entries.

FieldHexarelinIpamorelin
Encyclopedia entryHexarelin Full entryIpamorelin Full entry
Molecule classPeptidePeptide
CategoryGrowth HormoneGrowth Hormone
FDA statusResearch ChemicalDiscontinued
Approved elsewhereNone recordedNone recorded
Evidence gradeMediumMedium
Half-lifeNot measured in humans≈ 2 hours
FormulaC47H58N12O6C38H49N9O5
Molecular weight887.0 g/mol711.9 g/mol
WADA 2026Prohibited at all times (S2.2.4)Prohibited at all times (S2.2.4)
WADA 2027Prohibited at all times (S2.2.4)Prohibited at all times (S2.2.4)
In one lineA synthetic GH-releasing hexapeptide that outperformed GHRH in small 1990s human studies, also raised cortisol and prolactin, and lost part of its effect with months of use. Never approved.A ghrelin-receptor agonist that released growth hormone without raising cortisol in pigs; in people it has one dosing study and a phase 2 surgery trial that found no benefit. Never approved.
MechanismAgonist at the ghrelin receptor (GHS-R1a) on the pituitary and hypothalamus, releasing growth hormone and, less selectively, ACTH, cortisol and prolactin; synergistic with GHRH. Also binds CD36, a scavenger receptor in heart tissue that a 2014 review credits with its cardioprotective effects in animals. Repeated dosing partly blunts the growth hormone response, which recovers after stopping.Agonist at the ghrelin (GHRP) receptor that releases growth hormone with a potency close to GHRP-6's in rat pituitary cells and animals. In pigs it did not raise ACTH or cortisol even at more than 200 times its effective dose, unlike GHRP-6 and GHRP-2; that selectivity has not been measured in a published human study. As a ghrelin mimetic it speeds gut transit in rodents.
Sources in the entry1715
Study cards1714
Dosage pageDosage pageDosage page

How strongly each releases growth hormone

Hexarelin's human record shows a potent releaser. In a double-blind, placebo-controlled rising-dose study, single intravenous doses in 12 healthy men raised growth hormone to mean peaks of 26.9 to 55.0 ng/mL about 30 minutes later, against 3.9 ng/mL on placebo 4. It raised growth hormone promptly in all 45 short but otherwise normal children tested, exceeding the response to GHRH 5, and given with GHRH it released more than the sum of the two 6. When ghrelin itself became available, it released more growth hormone than hexarelin at the same dose, and both released more than GHRH 7.

Ipamorelin's potency has been measured mainly in animals: in rat pituitary cells, anaesthetised rats and conscious pigs it released growth hormone with potency and efficacy similar to GHRP-6, without the ACTH and cortisol rise that GHRP-6 and GHRP-2 caused 2. In people, the only data are pharmacokinetic: in 40 healthy men given single intravenous infusions at five doses, its kinetics were proportional to dose with a terminal half-life of about two hours 8. No study has compared the two directly in humans.

Tolerance: hexarelin's response fades

The most important human finding about hexarelin is that its effect does not hold. Adults who injected it under the skin twice daily for 16 weeks saw the growth hormone response to a test dose fall from 19.1 to 12.3 µg/L·h by week 4 and 10.5 by week 16, roughly halving, before it recovered to 19.4 four weeks after stopping 9. The cortisol response to the morning injection also shrank over the same period and recovered after stopping 10. In beagles given high doses twice daily, the response rose to a peak at week 3 and then fell below its starting level by week 6 11.

That pattern, a strong early response that fades with regular use, is the reason claims about long courses deserve scepticism. No comparable long-term study of ipamorelin in people has been published, so whether it would fade in the same way is unknown.

Hexarelin and the heart

Hexarelin also acts on the heart, apparently through a route separate from growth hormone. In seven men with growth hormone deficiency, who barely released any growth hormone in response, intravenous hexarelin still raised the heart's ejection fraction, as it did in controls 12. In healthy volunteers, intravenous growth hormone and hexarelin raised circulating growth hormone equally, but only hexarelin raised ejection fraction, within 15 minutes 13. A review describes CD36 as a specific cardiac receptor for hexarelin 14. These are short-term measurements in small groups and do not show any long-term benefit or safety in people. Ipamorelin has no comparable human cardiac data.

Ipamorelin's one efficacy trial

Ipamorelin's only efficacy test in people was a multicentre, double-blind phase 2 trial in 114 adults having bowel resection, given intravenous ipamorelin or placebo twice daily for up to seven days to speed the return of bowel function. It found no significant benefit 15. According to our entry, the FDA placed ipamorelin acetate in 503B Category 2 in 2023, and its 503A nomination was withdrawn 3. Hexarelin was never developed into a product; animal research on its cardiac effects continues 3.

Sleep and other hormones

Because these peptides act at night when growth hormone normally peaks, sleep effects matter. Four hourly doses of hexarelin given late in the evening reduced deep, stage 4 sleep in the first half of the night and raised growth hormone and prolactin through the night 16. In young men, hexarelin injected two or three times a day enlarged each growth hormone pulse rather than adding pulses 17. Ipamorelin has no published human sleep study.

How the differences add up (as of October 3, 2026)

Hexarelin has far more human data: dose-response studies, children, the heart, sleep and a 16-week course that showed tolerance. Ipamorelin has a cleaner hormonal profile in animals, a dosing study and a failed phase 2 trial. Neither is approved anywhere, neither has long-term safety data, and both are prohibited in sport 3. Doses mentioned on this page are those in the studies cited, not recommendations; our ipamorelin vs GHRP-6 comparison covers the selectivity question in more detail.

Frequently asked questions

Is hexarelin stronger than ipamorelin?

Hexarelin is a potent growth hormone releaser in human studies; ipamorelin's potency was shown in animals to be similar to GHRP-6. No human study has compared them directly.

Does hexarelin stop working?

Its effect fades with regular use: over 16 weeks of twice-daily injections the growth hormone response fell by about half, and it recovered four weeks after stopping.

Are hexarelin and ipamorelin legal?

Neither is approved as a medicine anywhere. Both are prohibited in sport under WADA's 2026 List.

Sources

  1. Deghenghi, R., et al. (1994). GH-releasing activity of Hexarelin, a new growth hormone releasing peptide, in infant and adult rats. Life Sci, 54(18), 1321-8. PMID: 7910650
  2. Raun, K., et al. (1998). Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol, 139(5), 552-61. PMID: 9849822
  3. Grey Peptides dataset records for both compounds (status, half-life and studied doses as sourced on each entry); read October 2, 2026.
  4. Imbimbo, B. P., et al. (1994). Growth hormone-releasing activity of hexarelin in humans. A dose-response study. Eur J Clin Pharmacol, 46(5), 421-5. PMID: 7957536
  5. Loche, S., et al. (1995). The growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, in short normal and obese children and in hypopituitary subjects. J Clin Endocrinol Metab, 80(2), 674-8. PMID: 7852535
  6. Massoud, A. F., et al. (1996). The effect of repeated administration of hexarelin, a growth hormone releasing peptide, and growth hormone releasing hormone on growth hormone responsivity. Clin Endocrinol (Oxf), 44(5), 555-62. PMID: 8762732
  7. Arvat, E., et al. (2001). Endocrine activities of ghrelin, a natural growth hormone secretagogue (GHS), in humans: comparison and interactions with hexarelin, a nonnatural peptidyl GHS, and GH-releasing hormone. J Clin Endocrinol Metab, 86(3), 1169-74. PMID: 11238504
  8. Gobburu, J. V., et al. (1999). Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res, 16(9), 1412-6. PMID: 10496658
  9. Rahim, A., et al. (1998). Growth hormone status during long-term hexarelin therapy. J Clin Endocrinol Metab, 83(5), 1644-9. PMID: 9589671
  10. Rahim, A., et al. (1999). The effect of chronic hexarelin administration on the pituitary-adrenal axis and prolactin. Clin Endocrinol (Oxf), 50(1), 77-84. PMID: 10341859
  11. Rigamonti, A. E., et al. (1999). Six-week treatment with hexarelin in young dogs: evaluation of the GH responsiveness to acute hexarelin or GHRH administration, and of the orexigenic effect of hexarelin. Eur J Endocrinol, 141(3), 313-20. PMID: 10474131
  12. Bisi, G., et al. (1999). Cardiac effects of hexarelin in hypopituitary adults. Eur J Pharmacol, 381(1), 31-8. PMID: 10528131
  13. Bisi, G., et al. (1999). Acute cardiovascular and hormonal effects of GH and hexarelin, a synthetic GH-releasing peptide, in humans. J Endocrinol Invest, 22(4), 266-72. PMID: 10342360
  14. Mao, Y., et al. (2014). The cardiovascular action of hexarelin. J Geriatr Cardiol, 11(3), 253-8. PMID: 25278975
  15. Beck, D. E., et al. (2014). 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, 29(12), 1527-34. PMID: 25331030
  16. Frieboes, R. M., et al. (2004). Hexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers. Psychoneuroendocrinology, 29(7), 851-60. PMID: 15177700
  17. Maccario, M., et al. (2002). Impact of two or three daily subcutaneous injections of hexarelin, a synthetic growth hormone (GH) secretagogue, on 24-h GH, prolactin, adrenocorticotropin and cortisol secretion in humans. Eur J Endocrinol, 146(3), 310-8. PMID: 11888836

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.

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