Ibutamoren

Mechanism (as reported)

A review and mechanistic studies in the provided sources describe growth hormone secretagogues (including ibutamoren) as stimulating GH and IGF-1 signaling and promoting pulsatile GH release subject to negative feedback. A structural study reports high-resolution cryo-EM structures of a GHSR–Gi signaling complex with ghrelin and ibutamoren, and suggests molecular binding/activation motifs near the agonist-binding pocket.

Key findings (each cites a source)

• A review article described growth hormone secretagogues (GHS) including ibutamoren as potent GH and IGF-1 stimulators that can improve body composition while ameliorating specific hypogonadal symptoms such as fat gain and muscular atrophy; it also noted limited clinical data and a paucity of evidence in men with hypogonadism. [PMID 32257855]
• A review of GH secretagogues reported that GHS promote pulsatile GH release subject to negative feedback and that available studies suggest GHSs are generally well tolerated, with some concern regarding increases in blood glucose related to decreased insulin sensitivity; it also emphasized that few long-term, rigorously controlled studies exist. [PMID 28400207]
• A double-blind randomized placebo-controlled crossover study investigated an orally active GH secretagogue mimic (MK-677/ibutamoren in the provided context) and found that adding the drug during caloric restriction improved nitrogen balance versus placebo, with increased GH response and significant increases in IGF-I during treatment. [PMID 9467534]
• A pediatric GH deficiency trial report described LUM-201 (ibutamoren) as a GH secretagogue receptor agonist under development and reported that LUM-201 elicited greater GH responses than standard GH secretagogues used in diagnostic tests across several stimuli in pediatric subjects. [PMID 35354138]
• A structural study reported high-resolution cryo-EM structures of the GHSR–Gi signaling complex with ghrelin and the synthetic agonist ibutamoren, and described molecular basis insights from binding/activation, including motifs near the agonist-binding pocket and observed coupling variations. [PMID 34737341]
• A study in thoroughbred horses characterized ibutamoren and its metabolites after oral administration using LC/HRMS, reporting 22 metabolites identified and stating that major metabolites were detectable up to 96 hours after a single dose, with ibutamoren persisting up to 72 hours. [PMID 35716382]
• A rat study reported that orally administered MK-677 increased peak GH concentrations shortly after administration but, after 6 weeks, did not increase body growth or serum IGF-I; it also reported that the GH response was abolished by 6 weeks and described desensitization-associated changes including increased hypothalamic somatostatin (SST) mRNA expression. [PMID 30450851]