Comparison
Ipamorelin vs MK-677
Both are gHRPs & ghrelin mimetics, so the meaningful differences are in kinetics, evidence and regulatory status.
On published evidence alone, MK-677 is the better documented of the two (clinical trials). That is a statement about the state of the literature, not a recommendation.
| Ipamorelin | MK-677 | |
|---|---|---|
| Class | GHRPs & ghrelin mimetics | GHRPs & ghrelin mimetics |
| Evidence | Preliminary human | Clinical trials |
| Human trials | ~5 | ~22 |
| Half-life | ~2 hours | ~24 hours |
| Reported range | 200-300 mcg | 10-25 mg |
| Frequency | 1-3x daily, on an empty stomach | Once daily |
| Routes | Subcutaneous | Oral |
| FDA approved | No | No |
| Research use only | Yes | Yes |
| Banned in sport | Yes | Yes |
| Studied for | Growth hormone elevation, Recovery, Sleep quality, Body composition | Growth hormone elevation, Appetite stimulation, Sleep depth, Lean mass |
| Reported side effects | Head rush on injection, Transient hunger, Water retention, Lethargy | Increased appetite, Water retention, Reduced insulin sensitivity, Lethargy, Numbness in extremities |
Ipamorelin
Ipamorelin is a pentapeptide agonist at the growth hormone secretagogue receptor, the same receptor targeted by endogenous ghrelin. Unlike the earlier GHRPs it produces a GH pulse without meaningful elevation of adrenocorticotropic hormone, cortisol or prolactin, which is the basis of its reputation as the cleanest compound in the class. It is short-acting and is typically dosed alongside a GHRH analog to exploit the synergy between the two receptor pathways.
MK-677
MK-677 is a spiropiperidine growth hormone secretagogue receptor agonist, not a peptide, though it is almost always discussed alongside them because it targets the same receptor as the GHRPs. Oral bioavailability and a roughly 24-hour half-life produce sustained elevation of GH and IGF-1 from once-daily dosing. The same sustained exposure drives its two characteristic problems: marked appetite increase and a consistent reduction in insulin sensitivity.
Ipamorelin vs MK-677: common questions
What is the difference between Ipamorelin and MK-677?
Both are gHRPs & ghrelin mimetics. Ipamorelin: The most receptor-selective of the growth-hormone-releasing peptides, notable for leaving cortisol and prolactin essentially unchanged. MK-677: An orally active, long-acting ghrelin-receptor agonist. Frequently grouped with peptides but chemically a non-peptide small molecule.
Which has stronger evidence, Ipamorelin or MK-677?
MK-677 has the stronger evidence base (clinical trials, about 22 human studies) compared with Ipamorelin (preliminary human).
Are Ipamorelin and MK-677 FDA approved?
Neither is FDA approved for any indication.
References
Regulatory and primary sources
- PubChem compound record (CID 9831659) ↗ · structure, identifiers, synonyms
- WADA Prohibited List ↗ · current year
- FDA: Unapproved drugs and "research use only" products ↗ · regulatory status of non-approved products
- CAS Registry Number 170851-70-4 ↗ · chemical identity
- PubChem compound record (CID 6450830) ↗ · structure, identifiers, synonyms
- CAS Registry Number 159752-10-0 ↗ · chemical identity
Published literature
- Injectable Peptide Therapy: A Primer for Orthopaedic and Sports Medicine Physicians.Am J Sports Med 2026.PubMed 41476424 · doi:10.1177/03635465251357593
- Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions.J Am Acad Orthop Surg Glob Res Rev 2026.PubMed 41490200 · doi:10.5435/JAAOSGlobal-D-25-00236
- Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance.Sports Med 2026.PubMed 41966639 · doi:10.1007/s40279-026-02437-0
- Therapeutic Peptides in Aesthetic, Metabolic and Endocrine Conditions: Effects, Safety, Clinical Applications, and Future Perspectives.Int J Mol Sci 2026.PubMed 42123471 · doi:10.3390/ijms27093890
- A new era of doping? Use of peptide and peptide-analog drugs in recreational and professional sport and bodybuilding: a critical review.J Sports Med Phys Fitness 2026.PubMed 41880199 · doi:10.23736/S0022-4707.26.17773-1
- Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers.Pharm Res 1999.PubMed 10496658 · doi:10.1023/a:1018955126402
- 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.PubMed 25331030 · doi:10.1007/s00384-014-2030-8
- Injectable Peptides in Sports Medicine: A Structured Narrative Review of Evidence, Safety, and Antidoping Implications.JBJS Rev 2026.PubMed 42160466 · doi:10.2106/JBJS.RVW.26.00027
- Growth hormone-releasing peptides.Eur J Endocrinol 1997.PubMed 9186261 · doi:10.1530/eje.0.1360445
- MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism.J Clin Endocrinol Metab 1998.PubMed 9467534 · doi:10.1210/jcem.83.2.4551
- The Safety and Efficacy of Growth Hormone Secretagogues.Sex Med Rev 2018.PubMed 28400207 · doi:10.1016/j.sxmr.2017.02.004
- Growth hormone-releasing peptides and their analogs.Front Neuroendocrinol 1998.PubMed 9465289 · doi:10.1006/frne.1997.0158
- New directions in growth hormone treatment in children.Pediatr Endocrinol Diabetes Metab 2025.PubMed 41693185 · doi:10.5114/pedm.2025.158544
- Growth hormone-releasing peptides and the cardiovascular system.Ann Endocrinol (Paris) 2000.PubMed 10790589
- Regulation of ghrelin secretion and action.Endocrine 2003.PubMed 14610293 · doi:10.1385/ENDO:22:1:5
- Ghrelin receptor (GHS-R1A) agonists show potential as interventive agents during aging.Ann N Y Acad Sci 2007.PubMed 18056963 · doi:10.1196/annals.1404.023
Literature retrieved from PubMed on October 16, 2026, favouring human studies and reviews. Numbered markers in the text show which paper supports which statement; uncited entries are background reading.