What is the difference between MK-677 and Ipamorelin?

MK-677: 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) ... Ipamorelin: Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) originally developed by Novo Nordisk and later advanced by Helsinn/Nycomed. It is a selective ghrelin receptor agonist / growth h...

MK-677 vs Ipamorelin

Q: Can you stack MK-677 and Ipamorelin?

MK-677 (performance) and Ipamorelin (performance) are in the same category and may have overlapping mechanisms — researchers should review both profiles carefully before combining. Consult a licensed provider before combining any compounds.

Head-to-head comparison of MK-677 and Ipamorelin — mechanism, dosing, side effects, legal status, and pricing.

MK-677

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.

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Ipamorelin

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) originally developed by Novo Nordisk and later advanced by Helsinn/Nycomed. It is a selective ghrelin receptor agonist / growth hormone secretagogue (GHRP). Its defining feature versus older GHRPs (GHRP-2, GHRP-6, hexarelin) is that in preclinical and early clinical studies it raised GH without meaningfully increasing ACTH, cortisol, or prolactin. It is not FDA-approved for any indication; a Phase 2 trial for postoperative ileus failed to meet its primary endpoint and clinical development was discontinued. In the wellness/grey market it is sold as a research chemical and used off-label for anti-aging and body-composition goals despite no clinically validated human dose for those uses.

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MK-677

Ipamorelin

Category

Performance

Legal Status

Research Only

Category 1 — Legally Compoundable

Mechanism

MK-677 is a selective agonist of the ghrelin receptor (GHSR-1a) on pituitary somatotrophs and hypothalamic neurons, driving pulsatile GH release and secondary IGF-1 elevation with once-daily oral dosing. Oral bioavailability is sufficient for sustained 24-hour effect. Unlike GHRPs, it does not significantly raise cortisol or prolactin at typical doses. It also stimulates appetite through hypothalamic ghrelin signaling.

Ipamorelin binds the growth hormone secretagogue receptor 1a (GHSR-1a) on pituitary somatotrophs and in the arcuate nucleus of the hypothalamus, mimicking endogenous ghrelin. GHSR-1a is a Gq-coupled GPCR; activation triggers phospholipase C, IP3, and intracellular calcium release, driving pulsatile GH secretion. Ipamorelin's selectivity appears to come from its distinct binding profile at the GHSR compared with GHRP-2/GHRP-6, producing GH release without substantial ACTH/cortisol or prolactin co-release at therapeutic doses. It is pharmacologically complementary to GHRH analogs (sermorelin, CJC-1295) because the two receptor systems converge on somatotroph GH release through different second messengers, producing additive-to-synergistic GH pulses when co-administered.

Dose Range

10–25 mg

200–300 mcg per dose (grey-market range)

Route

Oral

SubQ

Frequency

Once daily

1–3 times daily

Dosing Notes

Grey-market dosing, not a medical regimen. Typically taken at bedtime due to potential lethargy and GH-pulse timing; 25 mg was the most studied adult dose. Cycles of 8–16 weeks are common anecdotally. Appetite increase, water retention, and rising fasting glucose are expected within weeks. Not FDA-approved and not a 503A/503B compounding candidate.

There is no FDA-approved dose. Grey-market protocols typically inject 200–300 mcg subcutaneously 1–3 times per day (commonly pre-bed, pre-workout, and/or post-workout), often stacked with a GHRH analog such as CJC-1295 (no DAC) / modified GRF(1-29) to exploit GHRH+GHRP synergy. Administration on an empty stomach is favored because nutrients (especially carbohydrate and fat) blunt the ghrelin-axis GH response. None of these regimens have been validated in controlled human trials for body-composition or anti-aging endpoints.

Side Effects

Marked appetite increase (ghrelin-mediated)
Water retention, edema, and fluid-driven weight gain
Elevated fasting glucose and reduced insulin sensitivity
Lethargy and drowsiness
Paresthesias (numbness/tingling in extremities)
Muscle aches and joint stiffness (fluid-related)
Worsening of pre-existing congestive heart failure (documented trial signal)

Injection-site reactions (erythema, itching, transient welt)
Transient mild water retention / peripheral edema
Increased appetite (ghrelin-class effect)
Headache and flushing shortly after injection
Paresthesias (tingling or numbness in hands or feet)
Transient post-dose fatigue or lightheadedness
Reduced insulin sensitivity / elevated fasting glucose with sustained GH elevation, of particular concern when stacked with long-acting GHRH analogs in predisposed individuals

Contraindications

Congestive heart failure or significant cardiac dysfunction (trial-documented worsening)
Uncontrolled diabetes or significant insulin resistance
Active malignancy
Pregnancy or breastfeeding
History of pituitary tumor or uncontrolled acromegaly risk factors

Active or suspected malignancy (theoretical risk via GH/IGF-1 signaling on occult neoplasm)
Pregnancy and breastfeeding (no safety data)
Uncontrolled or poorly controlled diabetes mellitus, including type 2 diabetes with significant insulin resistance
Active acute or critical illness (GH-axis manipulation is associated with worse outcomes in ICU-level illness)
Known hypersensitivity to ipamorelin or excipients

MK-677 Research Summary

Short-term trials showed ~25–40% IGF-1 elevation and reversal of diet-induced nitrogen wasting (Murphy 1998, JCEM). A 2-year randomized trial in healthy older adults (Nass 2008, Ann Intern Med) restored GH/IGF-1 to young-adult levels and increased fat-free mass, but produced modest fasting glucose elevation and insulin resistance. A Phase IIb hip-fracture trial (Adunsky 2011) was halted early after a congestive heart failure safety signal (4/62 ibutamoren vs 1/60 placebo). Merck abandoned the program; the compound remains investigational with no approved indication.

Key references

Ipamorelin Research Summary

The seminal preclinical characterization (Raun et al., 1998) established ipamorelin as the first GHRP-receptor agonist with a GH-release selectivity comparable to GHRH, without raising ACTH or cortisol even at doses more than 200-fold above the ED50 for GH. Pharmacokinetic-pharmacodynamic modeling in healthy male volunteers (Gobburu et al., 1999) confirmed a roughly 2-hour half-life and dose-dependent GH response following IV infusion. The most advanced human study is Beck et al. (2014), a Phase 2, randomized, double-blind, placebo-controlled trial in 114 patients after bowel resection evaluating IV ipamorelin 0.03 mg/kg twice daily for postoperative ileus; the drug was well tolerated but did not separate from placebo on the primary endpoint (time to tolerance of solid food), and the sponsor discontinued development. There are no completed registrational trials in adult growth hormone deficiency, frailty, or body-composition indications. Use in wellness medicine for anti-aging, fat loss, or muscle gain is extrapolated from short-term GH/IGF-1 pharmacodynamic data and is not clinically validated.

Key references

Can you stack MK-677 and Ipamorelin?

MK-677 and Ipamorelin 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.

Other comparisons

BPC-157 vs TB-500 Semaglutide vs Tirzepatide Ipamorelin vs CJC-1295 CJC-1295 vs Sermorelin Semaglutide vs Liraglutide Selank vs Semax BPC-157 vs GHK-Cu Semaglutide vs Retatrutide

This platform provides informational tools only, not medical advice. This comparison is for educational purposes only. Consult a licensed provider.

MK-677

Ipamorelin

Ipamorelin Research Summary

Can you stack MK-677 and Ipamorelin?