MK-677, also called Ibutamoren, is built as a single, compact molecule rather than a strung-together sequence of amino acids, which is why researchers do not classify it as a peptide even though it works on a related hormone system. It turns on the ghrelin receptor located in the brain's hypothalamus and pituitary gland, the same switch flipped by the body's own natural hunger signal, and scientists have studied it as a pill-form way to prompt the body into releasing more of its own growth hormone.
What it is
MK-677 has no amino acid chain at all, so rather than running the sequence analysis normally used to identify peptides, scientists confirm what it is through ordinary small-molecule chemistry tests. It turns on the ghrelin receptor, known in the literature as GHS-R1a, which pushes the pituitary gland into releasing growth hormone in short bursts that mimic the body's own natural pattern.
Taken by mouth, MK-677 is reported to remain active for roughly a full day, which is why researchers typically give it just once daily in their study designs. Because of this oral route, it differs from growth hormone releasing peptides that require injection, a difference in how the study is run rather than in the underlying hormone system being examined.
How it is studied
MK-677 has been tested in randomized, placebo-controlled human trials, usually lasting about two months, taken once daily by mouth, while researchers tracked growth hormone and a related blood marker called IGF-1, bone turnover markers, and body composition. One larger trial studied older adults recovering from a hip fracture and was stopped early.
What studies report
- A multicenter trial in older adults recovering from a hip fracture was stopped early after researchers observed more cases of heart failure in the group taking MK-677 compared with placebo, establishing an important safety limit for this population. [1]
- A two month study in obese young men reported increases of 39 to 45 percent in a blood marker of new bone formation called osteocalcin, suggesting effects on bone turnover. [2]
- A two month randomized trial in adults with obesity reported increased growth hormone release, more fat-free body mass, and higher energy expenditure while treatment continued. [3]
What is not known
Because the hip fracture trial's heart failure signal was significant enough to end the study early, it is not known whether the compound is safe over long stretches in older adults or people with existing cardiovascular risk. Bone and body composition trials beyond two months were not identified in the citations reviewed, and effects in healthy, younger adults without an underlying condition are not directly covered by these three studies.
Reported adverse findings
- A trial in older adults recovering from a hip fracture was stopped early because of a higher rate of heart failure among participants taking MK-677 compared with those on placebo. [1]
Regulatory status
MK-677 is not approved by the United States Food and Drug Administration for any use, and regulators have specifically flagged a safety signal for congestive heart failure. Current FDA rules also do not permit it as an ingredient in a dietary supplement.
Research reporting only. Nothing on this site is medical advice, a diagnosis, or a recommendation to take, stop or change any medicine.
Sources
- MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb studyArchives of Gerontology and Geriatrics, 2011
- Treatment with the oral growth hormone secretagogue MK-677 increases markers of bone formation and bone resorption in obese young malesJournal of Bone and Mineral Research, 1998
- Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditureJournal of Clinical Endocrinology and Metabolism, 1998
Last reviewed 7 September 2026