Claimed effect · MK-677 (ibutamoren)

Does MK-677 (ibutamoren) help with fat loss?

B
Grade B — probable, not settled1 RCT (n=65) — no effect · effect size: not measurable
Short answerProbable, not settled. Human data exist (1 RCT (n=65) — no effect) and mostly agree, showing no measurable effect, or none yet shown — but too few, too small, or not yet peer-reviewed for a firm answer. Neither total fat mass nor abdominal visceral fat changed over a year; limb fat actually rose more on MK-677 than on placebo. Sold for fat loss, it did the opposite in the one trial that measured it.

What the studies show

Neither total fat mass nor abdominal visceral fat changed over a year; limb fat actually rose more on MK-677 than on placebo. Sold for fat loss, it did the opposite in the one trial that measured it.

“No significant differences were observed in abdominal visceral fat or total fat mass; however, the average increase in limb fat was greater in the MK-677 group than the placebo group (1.1 kg vs. 0.24 kg; P = 0.001).”

Verbatim, from the abstractNass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med, 2008;149(9):601–611

Human trials exist and mostly agree, but there are too few of them, they are too small, or one big one is still reading out. Expect the grade to move.

  1. 1

In context

MK-677 is a small molecule, not a peptide, that mimics the hunger hormone ghrelin and raises growth hormone and IGF-1 when taken by mouth. Unusually for a grey-market compound, it has been through proper trials. In 65 healthy older adults over a year it raised fat-free mass by about 1.1 kg against a 0.5 kg loss on placebo, with no change in total or visceral fat. In 563 people with Alzheimer's disease it raised IGF-1 by 73% and did nothing for the disease. It has never been approved anywhere and is prohibited in sport.

MK-677 (ibutamoren) is not approved. Legal status differs by country — see the regulation section or the jurisdiction pages.

Questions

Is MK-677 (ibutamoren) proven to help with fat loss?
Not yet settled. 1 RCT (n=65) — no effect — LYO grades it B, meaning probable but liable to change as trials read out.
What studies are behind the grade?
Neither total fat mass nor abdominal visceral fat changed over a year; limb fat actually rose more on MK-677 than on placebo. Sold for fat loss, it did the opposite in the one trial that measured it.
Is MK-677 (ibutamoren) approved for this?
No. MK-677 (ibutamoren) is not approved; it is not an approved medicine for any indication in the jurisdictions LYO covers.

Other outcomes for MK-677 (ibutamoren)

Written and maintained by LYO Research — how pages are written and checked. Reviewed 10 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →