Also known as: Ibutamoren (small molecule)
Ibutamoren (MK-677) is a small-molecule, non-peptide compound that mimics the hormone ghrelin at its receptor and is a ghrelin-receptor agonist studied in endocrine research. Research includes a handful of randomized human trials, mostly from the 1990s to 2010s, plus rodent studies.
Ibutamoren activates the ghrelin receptor (growth hormone secretagogue receptor), which signals the pituitary to release growth hormone [1][2]. In young rats, a single dose raised growth hormone, but after 6 weeks of daily exposure the growth hormone response was no longer seen; researchers measured higher hypothalamic somatostatin and lower pituitary somatostatin-receptor-2 expression and proposed these as the cause of that desensitization [2]. The desensitization mechanism is a proposal from one small rat study.
| Study | Model | Reported result | Source |
|---|---|---|---|
| Nass et al., 2-year trial [1] | Human 65 healthy adults aged 60-81, randomized, double-blind, placebo-controlled, modified crossover, 2 years | Primary endpoints: body-composition measures at 1 year (see publication). Published | Peer-reviewed Ann Intern Med 2008 |
| Adunsky et al., phase 2b [3] | Human 123 older adults in a post-surgical rehabilitation setting, randomized, double-blind, placebo-controlled, multicenter, planned 24 weeks | Primary endpoints: functional performance measures and blood IGF-1. Stopped early after a cardiac safety signal reported by the authors. Published | Peer-reviewed Arch Gerontol Geriatr 2011 |
| Lee et al., somatic growth study [2] | Rat Young female Sprague-Dawley rats, 4 per group, single dose and 6 weeks daily | Single dose: peak GH 45.7 ng/mL (1.8-fold baseline). After 6 weeks: GH response absent; no change in body length, growth plate width or IGF-I | Peer-reviewed Yonsei Med J 2018 |
Human trials are listed for research context only; outcomes are reported in the linked publications. Animal and lab results do not establish effects in humans.
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