MK-677 vs ipamorelin

Two ghrelin mimetics sold for the same reasons — which one has actually been tested for them?

No head-to-head trial — cross-trial comparison
In one paragraphBoth raise growth hormone; only MK-677 has been tested for what people buy it for. In a year-long randomised trial of 65 older adults it added about 1.1 kg of fat-free mass and changed no fat measure; in 563 people with Alzheimer's it did nothing clinically. Ipamorelin's only randomised trial tested post-operative gut recovery, was negative, and development stopped. Neither is approved. MK-677 is a pill and not a peptide; ipamorelin is an injected pentapeptide.

Side by side

B MK-677 (ibutamoren)C Ipamorelin
LYO gradeBC
What it isOral small molecule (ibutamoren), not a peptideInjected five-amino-acid peptide
Growth hormone / IGF-1 riseReliable; IGF-1 +60–73% in a 563-person trialReliable, acute, selective (little cortisol or prolactin)
Lean mass+1.1 kg vs −0.5 kg placebo over 1 year, n=65No trial
Fat lossNone — total and visceral fat unchanged; limb fat roseNo trial
Largest RCTn=563, Alzheimer's disease, 1 year — negativen=117, post-operative ileus — negative
Adverse effectsAppetite, fluid retention, higher fasting glucose and insulin resistanceWell tolerated over 7 days IV; no long-term data
Regulatory statusNot approved; investigational onlyNot approved; Category 2 (may not be compounded) in the US
Sport (WADA)Prohibited (S2)Prohibited (S2)
Verdict

MK-677 if the question is evidence: a real trial, a small lean-mass gain, no fat loss, and a clean negative in Alzheimer's. Ipamorelin has no body-composition trial at all. Both are banned in sport and unapproved everywhere.

The trial that matters

MK-677 is unusual among grey-market compounds in having been through a proper programme, because Merck developed it as a drug. The 2008 trial in healthy adults over 60 is the one to read: two years, placebo-controlled, with body composition measured properly. Fat-free mass rose by about 1.1 kg against a 0.5 kg loss on placebo — real, and small. Total fat and visceral fat did not change. The authors themselves called the functional benefit unproven. The 563-person Alzheimer's trial engaged the target — IGF-1 rose 60–73% — and moved none of four clinical measures.

What ipamorelin has instead

Novo Nordisk's early studies confirmed that ipamorelin releases growth hormone acutely and selectively. Its one randomised trial had nothing to do with muscle: 117 bowel-surgery patients were given it intravenously to speed gut recovery, and the difference from placebo was not significant. Development ended. No study has measured muscle, fat, sleep or recovery in anyone taking ipamorelin.

The shared problem

Raising growth hormone is easy to demonstrate and is what both compounds do. Turning that into a body-composition benefit in healthy adults is the claim, and the one compound that tested it found a kilogram of lean tissue, no fat loss, and worse glucose handling. There is no reason to expect a peptide with the same mechanism and no trial to do better.

Questions people actually ask

Is ipamorelin cleaner than MK-677?
It is more selective on cortisol and prolactin acutely, which is a pharmacological nicety. MK-677's problems in trials were appetite, fluid and glucose, which come from sustained GH elevation and would apply to any effective secretagogue.
Does MK-677 build muscle?
About a kilogram of fat-free mass over a year in older adults, in one trial, without a shown strength or function benefit. Not the effect the marketing implies.
Is either legal?
Neither is an approved medicine anywhere. Ipamorelin is on the FDA's list of substances that may not be compounded; MK-677 is an unapproved investigational drug. Both are banned in sport.

References

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