Claimed effect · MK-677 (ibutamoren)

Does MK-677 (ibutamoren) help with lean mass?

B
Grade B — probable, not settled1 RCT (n=65, 12 months) · effect size: small
Short answerProbable, not settled. Human data exist (1 RCT (n=65, 12 months)) and mostly agree, showing a small effect — but too few, too small, or not yet peer-reviewed for a firm answer. Fat-free mass rose by about 1.1 kg over a year against a 0.5 kg loss on placebo — a real difference, in one trial, in people over 60. Whether that becomes strength or function was not shown; the authors themselves called for functional studies.

What the studies show

Fat-free mass rose by about 1.1 kg over a year against a 0.5 kg loss on placebo — a real difference, in one trial, in people over 60. Whether that becomes strength or function was not shown; the authors themselves called for functional studies.

“Mean fat-free mass decreased in the placebo group but increased in the MK-677 group (change, -0.5 kg [95% CI, -1.1 to 0.2 kg] vs. 1.1 kg [CI, 0.7 to 1.5 kg], respectively; P < 0.001), as did body cell mass, as reflected by intracellular water (change, -1.0 kg [CI, -2.1 to 0.2 kg] vs. 0.8 kg [CI, -0.1 to 1.6 kg], respectively; P = 0.021).”

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 lean mass?
Not yet settled. 1 RCT (n=65, 12 months) — LYO grades it B, meaning probable but liable to change as trials read out.
What studies are behind the grade?
Fat-free mass rose by about 1.1 kg over a year against a 0.5 kg loss on placebo — a real difference, in one trial, in people over 60. Whether that becomes strength or function was not shown; the authors themselves called for functional studies.
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 →