Small-molecule ghrelin mimetic · Fact sheet
Ibutamoren
Also known as MK-677 · MK-0677 · Ibutamoren mesylate
Ibutamoren, often called MK-677, is a small molecule rather than a peptide or SARM. It increased growth hormone and lean mass in older adults, but did not improve strength or function in that trial and remains unapproved.
What is Ibutamoren?
Ibutamoren acts through the ghrelin receptor and stimulates the growth-hormone/IGF-1 pathway. A change in lean mass includes more than new functional muscle.
Benefits people look for
People look for greater appetite, muscle growth, recovery, sleep, and anti-aging effects. The human findings are more limited than this collection of claims.
What the evidence supports
- The older-adult trial found increases in growth hormone, IGF-1, and fat-free mass.
- It did not demonstrate better strength or physical function; hip-fracture findings were also unfavorable overall.
All research areas
- Age-related body composition
- Growth hormone and IGF-1
- Recovery after hip fracture
Anecdotal reports & lived experiences
Reports describe what someone noticed. They cannot establish cause, typical results, or how often a side effect happens.
No added hunger in one account; strong hunger and lethargy in another
The original poster described little change apart from possible better sleep. A commenter described easier exercise recovery but unwanted hunger, fluid retention and lethargy.
Despite the forum name, ibutamoren is not a SARM. Previous other-drug exposure, unverified products and subjective outcomes limit interpretation; the accounts do not establish muscle gain.
Read the contrasting MK-677 accounts ↗Side effects & risks
- Increased appetite, edema, muscle discomfort, higher fasting glucose, and reduced insulin sensitivity were reported in the older-adult trial.
- A hip-fracture trial was stopped for a congestive-heart-failure signal; risk may depend on the population.
This is a summary of the cited evidence, not a complete product label. A lack of human safety data does not establish safety.
Clinical research: how strong is it?
Early human evidenceA randomized study in 65 older adults found more fat-free mass without corresponding strength or function gains. A separate hip-fracture study was stopped early after a heart-failure safety signal.
Selected research to read
Randomized study in 65 adults; lean-mass increase without strength or functional improvement.
123-participant Phase IIb study terminated early after a heart-failure signal.
FDA approval & research status
Ibutamoren has no FDA-approved product. Historical trials in older adults do not establish approval for bodybuilding, recovery, or anti-aging.
No FDA-approved use is documented in the records summarized on this page.
No FDA-approved product
Ibutamoren has no FDA-approved product. Historical trials in older adults do not establish approval for bodybuilding, recovery, or anti-aging.
This summarizes the cited product or research record. Trial phases do not establish successful completion of earlier stages, and a stopped program is not ongoing development. Approval applies only to the labeled product, use and population.
What we still don’t know
- Whether body-composition changes improve long-term function
- Long-term cardiovascular and glucose effects
- Benefits and harms in younger performance-oriented users
The takeaway
MK-677 can change hormones and body composition, but the trials do not support equating those changes with better performance or healthy aging.
Sources & further reading
Medical evidence and regulatory sources are listed here. Personal reports are linked separately in the experiences section.
- 1fdaFDA: safety concerns for selected bulk substances
Ingredient-specific safety findings; compounding review is not drug approval.
- 2pubmedIbutamoren in healthy older adults
Randomized study in 65 adults; lean-mass increase without strength or functional improvement.
- 3pubmedIbutamoren after hip fracture
123-participant Phase IIb study terminated early after a heart-failure signal.