MK-677 — Research Dossier
Evidence grading
Class
Oral non-peptide GHS
Small-molecule ghrelin-receptor (GHS-R1a) agonist
Longest RCT
2 years
Nass et al. 2008, Ann Intern Med — healthy older adults
Half-life
~24 h
Once-daily dosing; IGF-1 elevation outlasts clearance
FDA approval
None
Remains investigational despite Phase II data
MK-677 is the most-studied oral GH secretagogue and the only one with a two-year randomised controlled trial — which confirmed durable IGF-1 elevation and fat-free-mass gain while recording no functional strength benefit and a documented metabolic-risk signal.
MK-677 (ibutamoren; development codes MK-0677, L-163,191) is a non-peptide ghrelin-receptor (GHS-R1a) agonist developed by Merck in the 1990s. Because it is a small molecule rather than a peptide, it survives oral dosing with bioavailability of approximately 60% — the feature that distinguishes it from all injectable secretagogues and makes it by far the most-studied oral compound in its class.
It was investigated for GH deficiency, muscle wasting and osteoporosis but, despite Phase II data including a two-year randomised controlled trial, was never approved by the FDA and remains investigational. Its ~24-hour half-life supports once-daily dosing and IGF-1 elevation that outlasts plasma clearance. The same ghrelin-mimetic activity drives appetite and tends to raise fasting glucose — the principal metabolic caution in the controlled-trial literature.
“The two-year randomised controlled trial found MK-677 increased fat-free mass and sustained GH/IGF-1 elevation without tolerance — and did not produce significant gains in muscle strength, function, or quality of life.”
— Nass R et al., Ann Intern Med 2008
Mechanism
MK-677 mimics ghrelin at GHS-R1a, driving sustained, largely non-pulsatile elevation of GH and IGF-1. Its ~24-hour half-life supports once-daily exposure and IGF-1 elevation outlasting plasma clearance — a pharmacokinetic advantage over injectable peptide secretagogues dosed two or three times daily. The same ghrelin-mimetic activity stimulates appetite and, importantly, tends to raise fasting glucose and reduce insulin sensitivity — the principal metabolic caution documented in the controlled-trial literature.
Clinical evidence base
GH/IGF-1 axis (established)
Chapman et al. (1996) showed daily oral MK-677 stimulated the GH-IGF-1 axis in older adults with reported increases in 24-hour GH secretion. Svensson et al. (1998) found two-month treatment in obese subjects increased GH, fat-free mass, and energy expenditure.
Two-year RCT (key human study)
Nass et al. (2008, Annals of Internal Medicine) — a two-year randomised, placebo-controlled trial in healthy older adults — found MK-677 increased fat-free mass and sustained GH/IGF-1 elevation without tolerance, with a mild increase in insulin resistance. Notably, it did not produce significant gains in muscle strength, function, or quality of life. This is the most rigorous human dataset for any oral GH secretagogue.
Bone (moderate)
Murphy et al. (1999, 2001) reported increased markers of bone turnover under MK-677, including in combination with alendronate in postmenopausal women — a moderate signal without fracture-endpoint data.
Negative result (Alzheimer's disease)
Sevigny et al. (2008, Neurology) found MK-677 had no clinical effect on Alzheimer's disease progression in a randomised trial. This is a clear negative outcome that bounds the compound's claims and should be weighed alongside the body-composition findings.
Regulatory and anti-doping status
MK-677 is not approved by the FDA, MHRA, or EMA and remains investigational. Material supplied for laboratory work is research-use only. As a GH secretagogue it is prohibited by WADA under category S2. The insulin-resistance and hyperglycaemia signal is a documented metabolic risk in the controlled-trial data and should be treated as a genuine finding, not a theoretical concern.
References
- 1
Chapman IM, Bach MA, Van Cauter E, et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996.
- 2
Svensson J, Lönn L, Jansson JO, et al. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998.
- 3
Nass 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.
- 4
Murphy MG, Plunkett LM, Gertz BJ, et al. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998.
- 5
Sevigny JJ, Ryan JM, van Dyck CH, et al. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology. 2008.
Research & Laboratory Use Only
This dossier is compiled for research planning and educational purposes only. It summarises published scientific literature and does not constitute medical advice, dosing guidance, or a therapeutic claim. All Nexyra Lab products are for research purposes only and are not for human or veterinary use. Nothing in this document should be interpreted as recommending, endorsing, or facilitating the self-administration of any compound.
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