MK-677

MK-677 is a non-peptide ghrelin mimetic. It binds the growth hormone secretagogue receptor (GHSR-1a) — the same one the hunger hormone ghrelin hits — and sets off pulsatile GH release from the anterior pituitary, which then raises IGF-1. Where the GHRH analogs (sermorelin, tesamorelin, CJC-1295) act upstream, MK-677 works directly on the GHSR. Two practical consequences follow: it is orally active, so no injections, and it ramps up appetite through that same ghrelin pathway — not what most people chasing body composition are hoping for.

MK-677 has more human RCT data than any other research-compound GH secretagogue, and reading those trials carefully cuts against its reputation. Nass et al. (2008, Ann Intern Med) randomized 65 healthy older adults for 12 months: GH and IGF-1 rose, fat-free mass climbed 1.6 kg over placebo — but insulin sensitivity worsened, fasting glucose and cortisol went up, and edema appeared. The fat-free mass bought no strength and no function. A larger RCT (Sevigny et al., 2008, Neurology; n=563) ran it in Alzheimer disease: IGF-1 jumped 72.9%, confirming the drug was engaging its target, and it was still ineffective at slowing the rate of progression of Alzheimer disease on every measure. Then the safety flag that matters most — a phase IIb trial in hip-fracture patients (Adunsky et al., 2011, Arch Gerontol Geriatr) was halted early over a congestive heart failure signal. No approved indication anywhere. For the older adults most drawn to GH support, that cardiac finding is not a footnote.

• Higher GH pulsatility and IGF-1 in healthy older adults (Nass 2008 RCT)
• A modest 1.6 kg fat-free-mass gain over placebo at 12 months — with no gain in strength or function (Nass 2008)
• Orally active — no injections, which is unique among GH secretagogues

• Increased fasting glucose and worsened insulin sensitivity — clinically meaningful risk for pre-diabetic or diabetic individuals (Nass 2008 RCT)
• Congestive heart failure safety signal: a phase IIb RCT in hip fracture patients was terminated early due to this finding (Adunsky et al., 2011, PMID 21067829)
• Appetite stimulation via ghrelin pathway; increased body weight reported in RCT (2.7 kg vs. 0.8 kg placebo)
• Elevated cortisol (~47 nmol/L increase in Nass 2008) and transient lower-extremity edema
• No evidence of cognitive benefit in Alzheimer disease despite dedicated RCT with clear target engagement (Sevigny 2008)
• No approved indication anywhere; long-term human safety is unknown
• Banned by WADA in sport
• Available only as an unregulated research compound; purity depends on source

Research compound. Sold "for research use only" — not approved for human consumption.

Goals studied: Body composition, GH / IGF-1 support

Is MK-677 a steroid?

No. MK-677 is a ghrelin mimetic — a synthetic molecule that mimics the hunger hormone ghrelin to stimulate GH release from the pituitary. It has no androgenic activity and is not structurally related to anabolic steroids.

Does MK-677 actually build muscle?

The 2008 Nass RCT showed modest increases in fat-free mass (+1.6 kg vs. placebo) in healthy older adults over 12 months. Critically, this did not translate to improved strength or functional performance. "Fat-free mass" also includes water and connective tissue. Anabolic effects in healthy younger adults have not been demonstrated in controlled trials.

Is MK-677 safe?

The RCT evidence raises real safety concerns: worsened insulin sensitivity and elevated blood glucose (Nass 2008), and a congestive heart failure signal leading to early termination of a trial in frail elderly patients (Adunsky 2011). Long-term safety data do not exist. The cardiac risk appears to be particularly relevant in older adults with pre-existing vulnerabilities.

1. [1]
   Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial

   Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE Jr, Clasey JL, Heymsfield SB, Bach MA, Vance ML, Thorner MO · Annals of Internal Medicine · 2008 · PMID 18981485 · model: human

   Twelve-month RCT in 65 healthy older adults: MK-677 raised GH and IGF-1 and increased fat-free mass (+1.6 kg vs. placebo), but worsened insulin sensitivity, raised fasting glucose, and caused edema — with no improvement in strength or function.

2. [2]
   Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial

   Sevigny JJ, Ryan JM, van Dyck CH, Peng Y, Lines CR, Nessly ML, MK-677 Protocol 30 Study Group · Neurology · 2008 · PMID 19015485 · model: human

   RCT in 563 Alzheimer disease patients: MK-677 25 mg/day raised IGF-1 by 72.9% (confirming target engagement), but was ineffective at slowing the rate of disease progression — no significant differences on any cognitive or functional measure.

3. [3]
   MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study

   Adunsky A, Chandler J, Heyden N, Lutkiewicz J, Scott BB, Berd Y, Liu N, Papanicolaou DA · Archives of Gerontology and Geriatrics · 2011 · PMID 21067829 · model: human

   Phase IIb RCT in hip fracture patients aged 65+: trial was terminated early due to a congestive heart failure safety signal; MK-0677 was concluded to have an unfavorable safety profile in this frail elderly population.