MK-677 (Ibutamoren)
An orally active, non-peptide ghrelin receptor agonist that drives sustained growth hormone and IGF-1 elevation from a single daily dose.
MK-677 is an orally active, non-peptide small-molecule ghrelin receptor (GHS-R1a) agonist developed by Merck as a research compound for growth hormone deficiency and muscle-wasting conditions. It mimics ghrelin to stimulate pulsatile GH and IGF-1 secretion from the pituitary, and is notable as one of the few GH secretagogues with confirmed oral bioavailability and a substantial human clinical dataset. Its defining feature is a ~24-hour half-life that produces sustained amplification of GH pulses throughout the day rather than the discrete pulses of injectable GHS peptides. Despite positive efficacy signals in Phase 2/3 trials, Merck discontinued development and MK-677 is not FDA-approved for any indication.
Class
Non-peptide small-molecule ghrelin receptor (GHS-R1a) agonist / oral growth hormone secretagogue
Half-life
~24 hours (oral)
Routes
Oral
Category
Growth Hormone & Performance
Researched benefits
What it's studied for
Oral GH and IGF-1 stimulation without injection
MK-677 is the only clinically studied oral growth hormone secretagogue, activating GHS-R1a to raise endogenous GH and IGF-1 from a single daily tablet or capsule, avoiding the reconstitution and injection required by peptide GHS compounds.
Sustained IGF-1 elevation
At the standard 25 mg/day dose IGF-1 typically rises ~80-100% above baseline and reaches steady state within 4-8 weeks; RCTs documented ~40% IGF-1 increase in obese men and a 65% greater rise than placebo in hemodialysis patients.
Increased fat-free mass
Randomized placebo-controlled trials demonstrated significant increases in fat-free mass by DXA, and the 2-year Nass trial in older adults showed measurable lean body mass gains (~1.1 kg at 24 months) with sustained IGF-1 elevation.
Improved slow-wave sleep architecture
Consistent with GHS pharmacology, MK-677 enhances slow-wave (deep) and REM sleep; users often report improved sleep within 3-7 nights as the most immediately noticeable effect.
Appetite stimulation
As a direct ghrelin-receptor agonist, MK-677 stimulates appetite via hypothalamic NPY/AgRP neurons, a benefit for underweight, hard-gainer, or muscle-wasting populations but a challenge in fat-loss contexts.
Recovery, connective tissue and bone support
Sustained GH/IGF-1 elevation is explored for enhanced recovery between training sessions, connective tissue and wound repair, and potential bone mineral density improvement.
Mechanism
How it works
MK-677 is a small-molecule full agonist at the growth hormone secretagogue receptor 1a (GHS-R1a) — the same Class A GPCR activated by endogenous ghrelin and by peptide GHS compounds such as ipamorelin, GHRP-2, GHRP-6 and hexarelin. Receptor binding on pituitary somatotrophs activates the Gq/11 / phospholipase-C pathway, cleaving PIP2 into IP3 and DAG; IP3 mobilizes intracellular calcium while DAG activates PKC, depolarizing the somatotroph and triggering rapid exocytosis of preformed GH granules. Its in vivo EC50 is approximately 1-3 nM, comparable to native ghrelin and the peptide GHS agonists.
What distinguishes MK-677 is its pharmacokinetics, not its receptor biology. Its ~24-hour plasma half-life produces sustained amplification of GH pulses throughout the day rather than the one or two discrete superimposed pulses of short-acting injectable GHS peptides. This is a double-edged property: it delivers consistent IGF-1 elevation, once-daily oral convenience, and stronger cumulative body-composition effects, but also greater water retention, more appetite stimulation, more insulin resistance, and theoretical concerns about somatotroph desensitization with prolonged use.
Despite sustained receptor engagement, MK-677 does not fully abolish pulsatile GH architecture — somatostatin-mediated negative feedback still modulates GH between pulses, so 24-hour profiling shows increased pulse amplitude and mean GH concentration without flattening the rhythm. This is a more physiologic profile than the continuous GH elevation of CJC-1295 with DAC, but less physiologic than ipamorelin's discrete pulses. Downstream, MK-677 produces the strongest sustained IGF-1 elevation of any oral or injectable GHS in non-GH-deficient adults, with IGF-1 rising ~50% by weeks 2-4 and reaching an ~80-100% elevation at steady state.
Because GHS-R1a is expressed beyond the pituitary — in the hypothalamic arcuate nucleus, gastric cells, pancreatic islets and cardiomyocytes — MK-677's sustained 24-hour agonism produces more prominent non-GH effects than short-acting peptides: appetite stimulation via NPY/AgRP neurons (potentially increasing caloric intake 20-30%), accelerated gastric emptying, multi-mechanism insulin resistance, and slow-wave sleep enhancement. Like ipamorelin, it is generally selective, producing minimal cortisol and prolactin elevation at clinical doses, though some cortisol elevation has been reported above 50 mg/day.
Dosing protocols
Dosing & administration
Dosing reflects protocols reported in research and community literature for educational purposes. It is not medical advice or a recommendation. Most peptides here are not approved for human use.
Standard / Low
- Dose
- 10 mg (10,000 mcg)
- Frequency
- Once daily
- Timing
- Pre-bed, empty stomach (2+ hours after last meal)
- Duration
- 8-16 weeks per cycle
- Route
- Oral
Lower dose expects ~40-50% IGF-1 elevation with reduced water retention and appetite stimulation; a good entry point and useful when pairing with a GLP-1 to keep appetite balanced.
Standard / Clinical
- Dose
- 25 mg (25,000 mcg)
- Frequency
- Once daily
- Timing
- Pre-bed, empty stomach
- Duration
- 8-16 weeks per cycle; up to 2 years in the Nass trial
- Route
- Oral
The most studied dose; produces ~80-100% IGF-1 elevation at steady state (4-8 weeks). Doses above 25 mg plateau on IGF-1 benefit but increase side effects proportionally.
Maintenance / Continuous
- Dose
- 10-25 mg
- Frequency
- Once daily
- Timing
- Pre-bed
- Duration
- Continuous with quarterly bloodwork
- Route
- Oral
The Nass-trial-reference approach is continuous dosing with periodic monitoring; the conservative alternative is cycling 8-16 weeks on / 4-6 weeks off. Long-term safety beyond 2 years is extrapolated from general GH/IGF-1 literature.
- Typical dose range is 10-25 mg orally once daily; doses above 25 mg/day provide minimal additional IGF-1 benefit while increasing side effects.
- Fasted dosing produces roughly 15% higher Cmax than fed dosing; pre-bed on an empty stomach maximizes absorption, aligns with the nocturnal GH burst, and enhances slow-wave sleep.
- Avoid high-fat meals immediately before dosing (they slow absorption); alcohol does not interact pharmacologically but impairs sleep — avoid within 4 hours of dosing.
- Monitor IGF-1, fasting glucose, insulin/HbA1c, blood pressure and weight; keep IGF-1 within age-adjusted reference range and discontinue if IGF-1 exceeds ~350 ng/mL.
- Expect 1-3 kg of scale weight from water retention in the first 2 weeks, stabilizing by week 4; add metformin 500-1000 mg/day if glucose management is a concern.
Evidence
Research & clinical studies (4)
Oral ghrelin receptor agonist MK-0677 increases serum insulin-like growth factor 1 in hemodialysis patients: a randomized blinded study
In a 3-month randomized crossover trial (n=22), oral MK-0677 produced a 65% greater increase in serum IGF-1 versus placebo in hemodialysis patients with no serious adverse effects, supporting the GH secretagogue pathway as a potential approach to protein-energy wasting in chronic kidney disease.
PMID 28340044Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure
In an 8-week randomized placebo-controlled trial (n=24), oral MK-677 25 mg daily increased serum IGF-I by ~40%, significantly increased fat-free mass by DXA, and transiently raised basal metabolic rate in obese men without significant changes in total or visceral fat.
PMID 9467542Effects of an oral ghrelin mimetic (MK-677) on body composition and physical function in older adults (2-year trial)
Over 2 years in older adults, MK-677 25 mg/day raised mean IGF-1 from ~180 to ~283 ng/mL and produced measurable lean body mass gains (~1.1 kg at 24 months) with a modest HbA1c rise; 3/32 active-arm patients developed transient congestive heart failure symptoms.
Prolonged oral treatment with MK-677 alters 24-hour GH secretory profile and pulsatility
24-hour GH profiling showed MK-677 increases both GH pulse amplitude and mean GH concentration without fully flattening the pulsatile rhythm, indicating preserved somatostatin-mediated feedback between pulses.
Combinations
Stacking & blends
MK-677 + Epithalon: Sleep Architecture & Anti-Aging
Improve sleep quality and support longevity-related outcomes
MK-677's ghrelin-mimetic enhancement of REM and slow-wave sleep plus GH pulse amplification is paired with Epithalon's research into pineal peptide bioregulation and telomere dynamics.
MK-677 + GLP-1 body recomposition
Preserve lean mass during fat loss
The GLP-1 drives caloric deficit and fat loss while MK-677 preserves lean body mass via GH/IGF-1 elevation; the opposing appetite effects (GLP-1 suppresses, MK-677 stimulates) net to a less aggressive but still hypocaloric state. Use MK-677 at 10 mg for a milder appetite balance.
MK-677 + TRT
Combined hormonal optimization
The HPG and GH axes are independent, so combined optimization is complementary and standard in integrative hormone clinics; add metformin 500-1000 mg/day if glucose management is a concern.
Safety
Side effects & considerations
Commonly reported effects
Contraindications & cautions
- History of congestive heart failure or NYHA class II-IV cardiac dysfunction
- Active malignancy
- Active diabetic retinopathy
- History of acromegaly or pituitary adenoma
- Pregnancy or breastfeeding
- Uncontrolled diabetes or significant insulin resistance
Glucose intolerance is real and dose-dependent — manage with diet, monitoring, and metformin if needed. Fluid retention should be monitored, especially with any cardiac history (CHF is an absolute contraindication). Keep IGF-1 within the age-adjusted reference range with periodic bloodwork. Discontinue and consult a clinician for chest pain, dyspnea, edema with >3 kg weight gain, worsening carpal tunnel, IGF-1 >350 ng/mL, or persistently elevated fasting glucose. WADA-banned for competitive athletes.
FAQ
MK-677 (Ibutamoren) — common questions
Is MK-677 a SARM or a steroid?
Neither. MK-677 is a growth hormone secretagogue — a small-molecule agonist at the ghrelin receptor (GHS-R1a) that stimulates the pituitary to release more growth hormone. It has no direct androgen receptor activity (unlike SARMs) and is not a steroid; it increases the body's own GH and IGF-1 rather than introducing exogenous hormones.
How much will MK-677 raise my IGF-1?
At the standard 25 mg/day dose IGF-1 typically rises 80-100% above baseline, reaching steady state within 4-8 weeks. In the Nass 2008 2-year trial in older adults, mean IGF-1 rose from 180 to 283 ng/mL. At 10 mg/day expect roughly 40-50% elevation. Above 25 mg the dose-response plateaus while side effects continue to increase.
Why does MK-677 cause more water retention and hunger than ipamorelin?
Its 24-hour half-life. Ipamorelin clears in ~2 hours, producing a discrete pulse and transient appetite effect, whereas MK-677 keeps the ghrelin receptor active around the clock. The continuous ghrelin signal drives hunger directly and the sustained GH elevation drives fluid shifts, which also explains its greater insulin resistance at equivalent total GH exposure.
Does MK-677 shut down natural GH production?
The evidence is nuanced. In the Nass 2008 2-year trial GH and IGF-1 stayed elevated throughout with no clear tachyphylaxis. Because MK-677 preserves some pulsatility, somatostatin feedback still operates between pulses, reducing but not eliminating desensitization risk. A conservative approach is cycling 8-16 weeks on / 4-6 weeks off; the trial-reference approach is continuous dosing with quarterly bloodwork.
Should I take MK-677 with food or on an empty stomach?
Empty stomach is preferred — fasted dosing produces ~15% higher Cmax. Pre-bed (2+ hours after the last meal) is standard because it maximizes absorption, aligns with the nocturnal GH burst, and enhances slow-wave sleep. It can be taken with food if needed, but avoid high-fat meals immediately before dosing.
Can I stack MK-677 with semaglutide or TRT?
Yes to both. With a GLP-1 (semaglutide or tirzepatide) it forms a recomposition stack — the GLP-1 drives fat loss while MK-677 preserves lean mass; use 10 mg MK-677 for a gentler appetite balance. With TRT the GH and HPG axes are independent and combined optimization is standard. Do NOT stack it with ipamorelin, GHRP-2/6 or hexarelin, which are also GHS-R1a agonists and therefore redundant.
Is MK-677 legal and is it banned in sports?
MK-677 is not FDA-approved and is sold in the US as a research chemical. WADA has banned it in competitive athletics since 2012 (S2 prohibited list), and it can produce a positive test for up to 6 weeks after discontinuation.
How long does it take to see results?
Sleep improvement is often noticeable within 3-7 nights, appetite increase within days, and 1-3 kg of water weight in the first 2 weeks (stabilizing by week 4). IGF-1 is detectable at week 2 and reaches steady state at 4-8 weeks, while lean body mass gains become measurable at 8-12 weeks and accrue over months. Effects reverse over 2-4 weeks after discontinuation.
