What is MK-677?
MK-677 (ibutamoren, development code MK-0677) belongs to a group called growth hormone secretagogues, meaning substances that prompt the body to release its own growth hormone. Merck researchers designed it in the 1990s as a non-peptide alternative to earlier growth hormone releasing peptides such as GHRP-6. Because it is a small molecule, it is orally active and survives digestion far better than those peptides, which is one reason it drew so much research interest.
Researchers tested it in healthy older adults, in people with growth hormone deficiency, in obesity and in Alzheimer's disease, but the original development program did not lead to a marketed medicine. More recently it has been studied again, under the code LUM-201, in clinical trials in children with certain forms of growth hormone deficiency.
How does MK-677 work?
MK-677 binds to the ghrelin receptor, also called the growth hormone secretagogue receptor, found in the pituitary gland and the hypothalamus. Activating it triggers pulses of growth hormone, and the liver responds by making more IGF-1, the hormone behind many of growth hormone's effects on muscle, bone and metabolism. Because it acts on the ghrelin receptor, it also tends to raise appetite. In trials, IGF-1 levels stayed higher with continued treatment, and small, short-lived rises in cortisol and prolactin were also reported.
What has MK-677 research looked at?
- Healthy older adults
- In a placebo-controlled trial in healthy adults in their 60s and 70s, MK-677 raised growth hormone and IGF-1 to levels typical of young adults and increased lean body mass. Researchers did not find meaningful gains in strength or physical function.
- Hip fracture recovery
- A trial in older adults recovering from hip fracture was stopped early over a safety concern, after more cases of heart failure were seen in the treated group.
- Bone
- Studies in older women reported increases in markers of bone turnover. Effects on bone density itself were modest and less clear.
- Muscle breakdown during calorie restriction
- A short study in healthy volunteers on a calorie-restricted diet found that MK-677 reduced nitrogen loss, a sign of protein breakdown.
- Sleep
- A small study reported changes in sleep structure, including more REM sleep and, in younger men, more deep sleep.
- Alzheimer's disease
- A year-long trial found that MK-677 did not slow the progression of Alzheimer's disease, even though it raised IGF-1.
MK-677 has more human data than most compounds in this library, but the trials were small or short. The consistent findings are higher growth hormone and IGF-1 levels and modest gains in lean mass, with much weaker evidence for better strength, function, sleep or fat loss.
Is MK-677 a peptide?
No. Peptides are chains of amino acids, and MK-677 is a small synthetic molecule with a completely different structure. It ends up in peptide conversations because it acts on the same receptor as growth hormone releasing peptides like GHRP-6 and ipamorelin. It is also not a SARM. SARMs act on androgen receptors, the receptor family testosterone uses, while MK-677 works through the growth hormone system and does not act on androgen receptors.
MK-677 side effects and cautions
The side effects reported most often in trials were increased appetite, mild swelling from fluid retention, and muscle aches. Fasting blood sugar tended to rise and insulin sensitivity tended to fall, which matters for anyone with prediabetes or diabetes. Because it raises IGF-1, which helps cells grow, a current or past cancer adds real uncertainty. Anyone with health questions about it should talk to a qualified clinician.
- Blood sugar
- Trials reported higher fasting glucose and lower insulin sensitivity, so blood sugar control is the main metabolic caution.
- Appetite and fluid
- It mimics a hunger hormone, so a rise in appetite is common, along with water retention and mild swelling, often in the legs.
- Heart failure
- The early stop of the hip fracture trial over heart failure cases is a reason for extra caution in older or frail people and anyone with heart disease.
- Cancer history
- Higher IGF-1 is a concern with any growth hormone axis compound in people with active cancer or a history of cancer.
- Other hormones
- Small, short-lived rises in cortisol and prolactin have been reported.
Further reading
This page summarizes the research in plain words. To read the studies yourself:
- Published studies on MK-677 PubMed, US National Library of Medicine
- Registered human trials of MK-677 ClinicalTrials.gov
