Biohackr: Track your protocol. Model the curve.

Educational reference only. Informational material drawn from peer-reviewed literature. Not medical advice and not a recommendation to use, dose, or modify any therapy. Decisions about hormone therapy should be made with a qualified healthcare provider.

Overview

MK-677 (also called Ibutamoren or ibutamoren mesylate, with development codes L-163,191 and MK-0677) is a non-peptide orally active growth hormone secretagogue developed by Merck Research Laboratories.

The compound is structurally distinct from the GHRPs (which are peptide-based) but mechanistically related: MK-677 acts as a selective agonist of the ghrelin receptor (GHS-R1a), the same receptor targeted by ipamorelin, GHRP-2, GHRP-6, and hexarelin, as well as endogenous ghrelin. This makes MK-677 functionally a non-peptide ghrelin mimetic with the practical advantage of oral bioavailability.

MK-677 has the most substantial Phase 2/3 clinical development history of any GH secretagogue: Merck conducted extensive trials across multiple indications between the late 1990s and 2011. None of these trials achieved approval, and the compound was ultimately abandoned by Merck. The development history includes:

563-patient Phase 3 Alzheimer's disease trial (Sevigny et al. 2008, PMID 19015485): primary endpoint not met
Phase IIb hip-fracture trial HALTED EARLY for congestive heart failure safety signal (Adunsky et al. 2011)
Multiple Phase 2 trials across other indications including growth hormone deficiency, osteoporosis, and aging

The 2011 hip-fracture trial halt for CHF safety signal is the most clinically significant event in MK-677's development. 4 patients (6.5%) on MK-677 developed congestive heart failure vs 1 (1.7%) on placebo, leading the data monitoring committee to stop enrollment early. The authors concluded the risk-benefit for this indication was not acceptable.

Forms

Available forms & half-lives

Form	Approximate half-life
Oral MK-677 (capsules/tablets)	~24 hours

What it does

Main effects

Substantial sustained GH and IGF-1 elevation: increases IGF-1 to levels typical of healthy young adults with chronic daily dosing; effects are sustained with once-daily dosing rather than pulsatile PMID: 18981485
Non-peptide oral bioavailability: ~60% oral bioavailability; ~24-hour half-life; once-daily oral dosing; the defining practical advantage over all peptide GHRPs
GHS-R1a (ghrelin receptor) agonism: same fundamental receptor as ipamorelin, GHRP-2, GHRP-6, hexarelin, and endogenous ghrelin; first non-peptide GHS-R1a agonist developed
Fat-free mass increase (~1.6 kg vs 0.1 kg placebo in Nass et al. 2008, 12-month healthy older adults trial)
Cortisol-sparing profile at typical doses: does NOT stimulate cortisol elevation to clinically significant degrees (advantageous vs GHRP-2/GHRP-6/hexarelin; similar to ipamorelin)
Sleep architecture effects: increased slow-wave sleep documented; vivid dreams common; improved sleep quality reported by some users
Appetite stimulation: significant; ghrelin-like signaling; more than ipamorelin, less than GHRP-6
Effects on energy expenditure documented in some studies

What to watch for

Common side effects

2011 Phase IIb hip-fracture trial HALTED for congestive heart failure safety signal: 4 of 62 patients (6.5%) on MK-0677 developed CHF vs 1 of 61 (1.7%) on placebo; data monitoring committee stopped enrollment; risk-benefit deemed unacceptable; this is the most clinically significant safety finding for MK-677 and is real human safety data, not theoretical concern
Phase 3 Alzheimer's disease trial (Sevigny et al. 2008, N=563) FAILED efficacy: IGF-1 successfully elevated but no benefit on AD progression at any primary or secondary endpoint; raises questions about whether IGF-1 elevation translates to meaningful clinical outcomes PMID: 19015485
Merck abandoned the MK-677 program (2011): following efficacy failures and the CHF safety signal; no further trials sponsored; no FDA filing for any indication
Substantial water retention and peripheral edema: common; may contribute to CHF risk in susceptible patients
Insulin resistance and elevated fasting glucose: documented in trials; more prominent than with intermittent peptide GHRPs due to sustained GH stimulation; caution in diabetic or prediabetic patients
Significant appetite increase: desired by some users, problematic for body composition goals
Lethargy and fatigue: commonly reported; possible relation to fluid retention
Possible blood pressure elevation in some users
Theoretical cancer concerns: sustained IGF-1 elevation with chronic use is theoretically concerning for cancer cell proliferation, dormant cancer activation, and long-term cancer risk
CYP3A4 metabolism: unlike peptide GHRPs, MK-677 has drug interactions with CYP3A4 inhibitors (ketoconazole, ritonavir, grapefruit juice) and inducers (rifampin, carbamazepine, St. John's wort)
Vivid dreams common: some find this disturbing
Active FDA enforcement: warning letters issued to companies selling MK-677 as supplements or research chemicals; not legal as dietary supplement or for human use
WADA, DoD, NFL/NBA/MLB/NHL, and NCAA all prohibit: extensive prohibition across competitive contexts
Product identity and purity are unverified: material sold as MK-677 in research chemical and supplement channels has documented identity problems, variable concentration, and mislabeling, so actual exposure is unknown
Long-term safety beyond 1 year not well-characterized in non-elderly populations

Key facts

Key facts worth knowing

MK-677 is NOT a peptide: this single fact distinguishes it from sermorelin, CJC-1295, ipamorelin, GHRP-2, GHRP-6, hexarelin, and tesamorelin. It is a small molecule (spiropiperidine) synthesized by traditional pharmaceutical chemistry. This enables oral bioavailability (~60%), 24-hour half-life with once-daily dosing, easier storage and stability than peptides, and manufacturing through standard pharmaceutical methods.
Mechanism is GHS-R1a (ghrelin receptor) agonism. Same fundamental receptor as the GHRPs. MK-677 was the first non-peptide GHS-R1a agonist developed, paving the way for oral GH secretagogue therapy that peptide GHRPs could not provide.
Substantial GH and IGF-1 elevation. Increases GH and IGF-1 levels into the upper portion of the normal range or above with chronic use. Effects are sustained with once-daily dosing rather than pulsatile. PMID: 18981485
Selectivity profile is favorable vs older GHRPs. Does not stimulate cortisol elevation to clinically significant degrees (unlike GHRP-2, GHRP-6, hexarelin). Generally considered "clean" for cortisol effects, similar to ipamorelin.
Phase 3 Alzheimer's trial failed efficacy: 563 patients, 12 months, MK-677 25 mg daily vs placebo. IGF-1 was successfully increased but no benefit on Alzheimer disease progression on any primary or secondary endpoint. PMID: 19015485
Hip-fracture Phase IIb trial halted for safety. Congestive heart failure signal in elderly patients (6.5% MK-677 vs 1.7% placebo). Risk-benefit deemed unacceptable. The trial halt is the most clinically significant event in MK-677's development history.
Significant practical concerns: Substantial water retention, increased appetite, lethargy, elevated fasting glucose, increased blood pressure in some users, and (importantly) the cardiovascular safety signal from the halted hip-fracture trial.
DoD and WADA Prohibited. On the Department of Defense Prohibited Dietary Supplement Ingredients List and the WADA Prohibited List. FDA has issued warning letters to companies illegally selling MK-677 products labeled as "supplements" or "research chemicals."

Legal status