MK-677 (ibutamoren)Non-peptide growth-hormone secretagogue
Ibutamoren, also called MK-677, is a small molecule rather than a peptide. It stimulates the ghrelin receptor and has been studied for effects on growth hormone, body composition and physical function.
Before comparing this entry. This name is retained to reconcile the source index. Its classification needs separate checking; inclusion does not establish that it is a peptide.
What is MK-677 (ibutamoren)?
Ibutamoren, or MK-677, is an orally active small molecule studied as a growth-hormone secretagogue. Despite its placement in peptide catalogues, it is not a peptide.
How it works
It stimulates the ghrelin receptor, which influences growth-hormone release and appetite. GH and IGF-1 concentrations are biological responses, not measures of strength.
Effects studied
Fat-free mass and physical function
In a trial of 65 healthy adults aged 60–81, fat-free mass increased after a year, but strength and physical function did not improve. Fat-free mass includes water as well as muscle, so the change cannot be read as a gain in useful muscle alone. 1
Evidence: Human trial in older adults
An early finding about sleep
A small 1997 study gives the sleep question a real research basis. In 8 young adults, short placebo-controlled treatment periods showed changes in deep and REM sleep; a separate group of 6 older adults also showed changes in sleep measurements. These brief experiments suggest an effect on sleep architecture. They do not establish treatment for insomnia or lasting improvements in how rested people feel. The glucose and heart-failure concerns remain relevant. 3
Evidence: Small, short human sleep experiments; preliminary signal, not an established clinical sleep benefit.
What does the evidence show?
Human trials in older adults and disease-specific populations
Why it appears in peptide catalogues
Ibutamoren acts on the same growth hormone secretagogue receptor targeted by some peptides, but its chemical structure is different. Its oral activity also distinguishes it from many injected research compounds. Similar marketing categories do not make these substances biologically or clinically interchangeable.
The important distinction in body composition
In a trial of 65 healthy adults aged 60–81, fat-free mass increased after a year, but strength and physical function did not improve. Fat-free mass includes water as well as muscle, so the change cannot be read as a gain in useful muscle alone. 1
Why the starting population matters
The study did not establish better athletic performance or slower ageing. Its size and duration also limited what it could say about function and uncommon harms. 1
An early finding about sleep
A small 1997 study gives the sleep question a real research basis. In 8 young adults, short placebo-controlled treatment periods showed changes in deep and REM sleep; a separate group of 6 older adults also showed changes in sleep measurements. These brief experiments suggest an effect on sleep architecture. They do not establish treatment for insomnia or lasting improvements in how rested people feel. The glucose and heart-failure concerns remain relevant. 3
The metabolic trade-off
Fasting glucose increased and insulin sensitivity declined in that trial. Increased appetite, swelling of the lower legs and muscle pain were common side effects. 1
The FDA also flags a potential heart-failure risk: a separate trial in patients recovering from hip fracture was stopped early after a safety signal. That finding should not be hidden behind a general statement that MK-677 was well tolerated in healthy older adults. 2
Safety & status
Fasting glucose increased and insulin sensitivity declined in that trial. Increased appetite, swelling of the lower legs and muscle pain were common side effects. 1
The FDA also flags a potential heart-failure risk: a separate trial in patients recovering from hip fracture was stopped early after a safety signal. That finding should not be hidden behind a general statement that MK-677 was well tolerated in healthy older adults. 2
Country and product status
Product indications and availability vary by country; current EU and Swiss status has not been independently checked for this draft.
Frequently asked questions
Is MK-677 a peptide?
No. It is a small molecule that acts on a receptor also targeted by some peptides.
Does more fat-free mass mean more functional muscle?
No. Fat-free mass includes water, and the trial did not show improved strength or physical function. 1
Sources
This entry was rewritten from our research archive. References below are reading leads unless a completed check is explicitly noted; a full independent evidence and regulatory review is still pending.
- Nass et al. (2008): Oral ghrelin mimetic in healthy older adults Primary research · PubMed abstract; full paper and supplements not reviewed; checked 2026-10-29
- FDA: Compounding substances with potential significant safety risks US regulator · Relevant substance entry; US safety notice, not an EU authorisation assessment; checked 2026-10-29
- Copinschi et al. (1997): Prolonged oral treatment with MK-677 improves sleep quality in man Early human sleep study · PubMed abstract; full paper not reviewed; checked 2026-10-29
Research provenance
This name was discovered in the Superpower peptide index, archived 26 October 2026. Its ratings and reviewer attribution have not been adopted as our own. The archive informed this original editorial draft; independent source review is still pending.