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MK-677
Based primarily on community reports and observational data
An orally active growth hormone secretagogue that mimics ghrelin to stimulate GH and IGF-1 release, notable for being a non-peptide small molecule rather than an injectable peptide.
Overview
MK-677 (Ibutamoren) is a non-peptide, orally active growth hormone secretagogue developed by Merck. Despite being frequently discussed alongside peptides, MK-677 is technically a small organic molecule that mimics the action of ghrelin by binding to and activating the GHS-R1a (ghrelin receptor) in the hypothalamus and pituitary gland. This stimulates the release of growth hormone in a pulsatile manner, and consequently increases IGF-1 levels.
The key advantage of MK-677 over peptide growth hormone secretagogues is its oral bioavailability — it can be taken as a pill rather than requiring injection. After oral administration, MK-677 produces a sustained increase in GH pulsatility and IGF-1 levels for up to 24 hours, allowing once-daily dosing. Studies have shown it can increase IGF-1 levels by 40-97% in various populations, maintaining these elevations with long-term treatment.
Clinical research on MK-677 has been relatively extensive compared to many research peptides. Studies in elderly populations showed improvements in body composition, bone mineral density, sleep quality, and nitrogen balance. A notable study in elderly subjects found that MK-677 restored the GH secretory pattern to that typical of young adults. Research in growth hormone-deficient adults showed comparable IGF-1 increases to injectable GH therapy at certain doses. Studies also demonstrated improved REM sleep and slow-wave sleep quality.
Despite positive clinical data, MK-677 has never received FDA approval. Concerns about sustained IGF-1 elevation, appetite stimulation (related to ghrelin-mimetic activity), potential insulin resistance with long-term use, and water retention have limited its commercial development. A large-scale study in elderly hip fracture patients (the MK-677 Study Group) showed no improvement in functional recovery despite increases in GH and IGF-1, raising questions about whether GH elevation alone is sufficient for therapeutic benefit in this population.
## Key PubMed References
[1] Chapman IM, et al. "Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretagogue (MK-677) in healthy elderly subjects." J Clin Endocrinol Metab. 1996;81(12):4249-57. PMID: 8954023
[2] Murphy MG, et al. "MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism." J Clin Endocrinol Metab. 1998;83(2):320-5. PMID: 9467534
[3] Nass R, et al. "Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults." Ann Intern Med. 2008;149(9):601-11. PMID: 18981485
[4] Bach MA, et al. "Is there a role for growth hormone secretagogues in the treatment of frail elderly patients?" Endocrine. 1999;11(3):263-7. PMID: 10786826
[5] Copinschi G, et al. "Effects of a 7-day treatment with a novel, orally active, growth hormone (GH) secretagogue, MK-677, on 24-hour GH profiles, insulin-like growth factor I, and adrenocortical function in normal young men." J Clin Endocrinol Metab. 1996;81(8):2776-82. PMID: 8768828
