Informational only. Not medical advice.INFORMATIONAL PLATFORM ONLY — NOT MEDICAL ADVICE, DIAGNOSIS, OR TREATMENT
Informational only. Not medical advice.INFORMATIONAL PLATFORM ONLY — NOT MEDICAL ADVICE, DIAGNOSIS, OR TREATMENT
Head-to-head comparison of GHRP-2 and MK-677 — mechanism, side effects, legal status, and pricing.
GHRP-2 (pralmorelin) is a synthetic hexapeptide ghrelin receptor agonist that stimulates pituitary growth hormone release. It is approved in Japan (Kaken Pharmaceutical, 2004) as a single-dose diagnostic agent for GH deficiency, but is NOT FDA-approved in the US and is research-only. Unlike ipamorelin, GHRP-2 is non-selective and modestly raises ACTH, cortisol, and prolactin.
MK-677 (ibutamoren, MK-0677, L-163,191) is an orally active, non-peptide small-molecule growth hormone secretagogue developed by Merck in the 1990s. It is a spiropiperidine ghrelin-receptor (GHSR-1a) agonist — not a peptide and not a SARM, though it is commonly misclassified as both in grey-market retail. Merck discontinued development after mixed efficacy and adverse metabolic / cardiovascular findings; it is not FDA-approved.
GHRP-2
MK-677
Category
Legal Status
Mechanism
Half-life
Side Effects
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GHRP-2
MK-677
No pricing data yet.
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GHRP-2
13
COAs
99.3%
Avg purity
6
Labs
MK-677
5
COAs
98.3%
Avg purity
3
Labs
GHRP-2 is among peptides under FDA review for the Category 1 (503A) list; if added, it would require a prescription to be compounded by registered 503A/503B pharmacies — not yet authorized. MK-677 remains research-only. In April 2026 the FDA removed 12 peptides from Category 2, which does not place them on the Category 1 list or authorize compounding. The FDA's Pharmacy Compounding Advisory Committee is advisory and meets July 23–24, 2026 to review nominations and make recommendations to the FDA.
GHRP-2 is approved in Japan (Kaken Pharmaceutical, 2004) as pralmorelin for single-dose diagnostic GH-stimulation testing; Chihara et al. (2007, PMID 17609397) validated a 100 mcg IV dose with a peak-GH <15 mcg/L cut-off against the insulin tolerance test. Arvat et al. (1997, PMID 9285939) showed GHRP-2 raises GH, prolactin, ACTH, and cortisol in healthy men, with hormonal effects similar to hexarelin. Laferrère et al. (2005, PMID 15699539) demonstrated that IV GHRP-2 significantly increases food intake in healthy men, consistent with its ghrelin-like activity. Pralmorelin review: Drugs R D 2004 (PMID 15230633). GHRP-2 is more potent than ipamorelin for raw GH output but is non-selective; grey-market anti-aging, muscle-gain, and performance use is not clinically validated in the US.
Key references
MK-677 has meaningful human data from Merck-sponsored Phase I/II trials. Murphy et al. (JCEM 1998, PMID 9467534) showed 25 mg MK-677 reversed nitrogen wasting during caloric restriction in healthy adults. Svensson et al. (JCEM 1998, PMID 9467542) reported ~40% IGF-1 elevation, increased fat-free mass, and higher energy expenditure over 8 weeks in obese men. Copinschi et al. (Neuroendocrinology 1997, PMID 9349662) documented improved slow-wave and REM sleep in young and older adults. Nass et al. (Ann Intern Med 2008, PMID 18981485) — the pivotal 2-year randomized trial in 65 healthy older adults — restored GH and IGF-1 to young-adult levels and increased fat-free mass, but produced modest fasting glucose elevation and insulin resistance. The Adunsky et al. Phase IIb hip-fracture trial (Arch Gerontol Geriatr 2011, PMID 21067829) was stopped early after a congestive-heart-failure safety signal (4/62 ibutamoren vs 1/60 placebo). Merck discontinued development. MK-677 is commonly mislabeled as a 'SARM' in grey-market retail — it is not; it is a ghrelin-receptor agonist and oral GH secretagogue. It has never been FDA-approved.
GHRP-2 and MK-677 are both in the Performance category and may have overlapping mechanisms. Researchers should review both profiles carefully, understand the mechanisms of action, and monitor the relevant biomarkers when combining compounds in the same class. As always, consult a licensed healthcare provider before making any decisions about combining research compounds.
This platform provides informational tools only, not medical advice. This comparison is for educational purposes only. Consult a licensed provider.
Contraindications
Lab Testing
Key references
Disclosed Labs