MK-677 (Ibutamoren)

Step	Weeks	Dose	Purpose
Weeks 1–2	—	10 mg	Assess appetite and water retention
Weeks 3–8	—	15–20 mg	Body composition protocol
Weeks 9+	—	25 mg	Maximum GH/IGF-1 elevation — monitor glucose

Beginner Protocol

Intermediate Protocol

Advanced Protocol

Reconstitution and handling notes

Stacking Notes

Additional Dosage Notes

MK-677 has a substantial clinical evidence base from Merck's development program, despite never reaching FDA approval.

Pivotal 2-year trial in older adults - Nass et al., 2008

The largest and longest MK-677 trial: 65 healthy adults aged 60-81, randomized to MK-677 25 mg/day or placebo for 2 years. Results:

• IGF-1 rose from 180 to 283 ng/mL (57% increase, within age-adjusted reference range)
• Lean (fat-free) mass increased 1.1 kg vs a 0.5 kg decrease on placebo at 1 year (P < 0.001); confirmed in the 2-year exploratory analysis
• Body weight rose 2.7 kg vs 0.8 kg on placebo
• No significant change in strength or function
• Fasting glucose rose ~5 mg/dL and insulin sensitivity fell; a small cortisol rise was seen
• Generally well tolerated - the most frequent adverse effects were increased appetite (which subsided within a few months) and transient, mild lower-extremity edema and muscle pain; no congestive heart failure occurred in this trial

This is the foundational long-term safety and efficacy citation for MK-677 (Nass et al., 2008).

First human PK/PD - Murphy et al., 1998

Single-dose pharmacokinetic study in healthy men: established the ~24-hour plasma half-life, oral bioavailability ~60%, dose-linear IGF-1 elevation from 10-50 mg, and the characteristic mild appetite stimulation and transient fluid retention. Validated the 25 mg once-daily dosing regimen ([Murphy et al., 1998]).

Dose-response characterization - Chapman et al., 1996

Randomized dose-escalation in healthy adults from 5 to 50 mg oral. Peak plasma GH increased dose-dependently, IGF-1 rose ~70% at 25 mg, and the dose-response plateaued above 25 mg/day - the evidence basis for the 25 mg/day dose that became standard ([Chapman et al., 1996]).

Sleep architecture - Copinschi et al., 1997

Polysomnographic evaluation showed MK-677 increased stage 4 slow-wave sleep (SWS) duration by 50% and REM sleep by 20%, with corresponding GH pulse amplification during SWS. The mechanistic basis for the universally-reported sleep improvement on MK-677 ([Copinschi et al., 1997]).

Hip fracture recovery - Adunsky et al., 2011

Multicenter, randomized, double-blind Phase IIb trial in 123 elderly patients recovering from hip fracture (MK-677 25 mg/day, n=62, vs placebo, n=61, for 24 weeks). IGF-1 rose ~51 ng/mL vs placebo (P < 0.001) and gait speed improved, but most objective functional-performance endpoints did not beat placebo. The trial was terminated early because of a congestive-heart-failure safety signal in a small number of patients, and the authors concluded MK-677 had an unfavorable safety profile in this population. This hip-fracture trial - not the Nass trial - is the actual source of the CHF safety signal for MK-677 (Adunsky et al., 2011).

Pediatric GH deficiency - Codner et al., 2001

Short-term dosing study in 18 prepubertal children with idiopathic growth hormone deficiency. Weight-based oral ibutamoren mesylate (0.2-0.8 mg/kg/day) was given for 7-8 days, with hormonal endpoints only - serum GH, IGF-1, and IGFBP-3. At 0.8 mg/kg/day the median GH peak, IGF-1, and IGFBP-3 all rose significantly from baseline, showing the compound can stimulate the GH/IGF-1 axis in some GH-deficient children. This was a short proof-of-mechanism study; it did not measure height velocity or growth outcomes (Codner et al., 2001).

Class review - Sigalos & Pastuszak, 2018

Comprehensive review covering MK-677 alongside the peptide GHS compounds in the context of male hormone optimization. Frames MK-677 as the orally-convenient alternative with the trade-offs of sustained receptor engagement vs pulsatile peptide pharmacology ([Sigalos & Pastuszak, 2018]).

What's missing from the evidence base

• No long-term (>2 year) safety data in healthy biohacking populations
• No direct head-to-head vs injectable peptide GHS (ipamorelin, tesamorelin)
• No data specifically addressing the 10 mg low-dose protocol commonly used in biohacking
• Cardiovascular outcomes beyond the 2-year Nass trial
• IGF-1-related cancer risk framework is extrapolated from broader GH/IGF-1 literature

The Merck discontinuation context

Merck halted MK-677 development due to a combination of factors:

• Failure to improve most functional endpoints in the hip-fracture Phase IIb trial
• A congestive-heart-failure safety signal that terminated the Adunsky hip-fracture trial early
• Questions about long-term somatotroph desensitization
• Commercial priorities

The CHF signal is real data from the Adunsky hip-fracture trial and informs the cardiac contraindication; by contrast, the 2-year Nass trial in healthy older adults reported no CHF. MK-677 never advanced beyond Phase II - no Phase III efficacy trial was ever completed.

MK-677 has the most pronounced side-effect profile of any GHS compound - specifically because its 24-hour half-life produces sustained rather than pulsatile receptor engagement. Users should expect all of the side effects listed below at some frequency.

Common (>20% of users, nearly universal at 25 mg/day)

• Appetite increase - the signature MK-677 effect; direct ghrelin-receptor agonism on hypothalamic feeding neurons. Can increase caloric intake by 20-30% if not actively controlled. Primarily evening and nocturnal (because that's when the pre-bed dose peaks)
• Water retention / mild peripheral edema - fluid-shift from GH and IGF-1 elevation plus sustained ghrelin-receptor tone. Typically 1-3 kg of scale weight in the first 2 weeks; settles by week 4 in most users; peripheral edema should resolve by week 6-8
• Lethargy / "heavy" feeling - particularly in the first 2-3 weeks; fluid-related; most users report this resolves but some stay lethargic through the cycle
• Vivid dreams / altered sleep - usually positive (deeper SWS) but can be disruptive in the first week
• Transient mild numbness / tingling in hands - water-retention-related peripheral nerve compression; early sign to reduce dose

Uncommon (5-20%)

• Insulin resistance / elevated fasting glucose - real and dose-dependent; HbA1c rises ~0.1-0.3% in Phase II data; meaningful for pre-diabetics and diabetics
• Mild carpal tunnel symptoms - fluid-related; resolves on cessation; should prompt dose reduction
• Joint stiffness - IGF-1-mediated connective tissue effect; typically weeks 4-8; often resolves with continued dosing
• Mild elevation in liver enzymes (ALT/AST) - usually within normal limits; monitor but rarely clinically significant

Rare but important

• Congestive heart failure signal - the CHF safety signal for MK-677 comes from the Adunsky 2011 hip-fracture Phase IIb trial (25 mg/day, N=123), which was terminated early after a small number of frail elderly patients developed CHF; it is attributed to fluid retention in vulnerable populations. The 2-year Nass trial in healthy older adults reported no CHF. This is the primary safety signal driving the "not in CHF, not in severe cardiac disease" contraindication
• Pituitary desensitization concerns - theoretical; not conclusively demonstrated in the 2-year trial but some users report reduced subjective response after 3-4 months of continuous dosing
• Elevated prolactin - rare at clinical doses but reported at higher doses; unique among "selective" GHS agents but dose-related

Insulin resistance - the honest framing

MK-677's effect on glucose metabolism is the most clinically important difference vs injectable GHS peptides. Mechanism:

• Direct GH-mediated hepatic glucose output increase
• Sustained ghrelin-receptor activation has independent glucose-intolerant effects
• Water retention complicates interpretation of labs

In Phase II data, HbA1c rose ~0.1-0.3% on MK-677 25 mg/day over 6-24 months. This is clinically small but not trivial:

• For healthy users: usually not clinically meaningful
• For pre-diabetics (fasting glucose 100-125 or HbA1c 5.7-6.4%): can push into overt T2DM territory
• For established T2DM: requires insulin/metformin adjustment and close monitoring

What MK-677 does NOT do (or does less than)

• Does NOT significantly elevate cortisol (unlike GHRP-6 / hexarelin)
• Does NOT significantly elevate ACTH
• Does NOT cause injection-site reactions (it's oral)
• Does NOT cause the pulse-amplitude sleep disturbance some users get from injectable GHS

Long-term uncertainty

The Nass 2-year trial is the longest data we have. Beyond 2 years, safety is extrapolated:

• Chronic hyperinsulinism effects
• IGF-1-related cancer risk
• Pituitary somatotroph reserve
• Cardiovascular outcomes in the broader population (the Nass cohort was older adults, not the 25-45 year old biohacker demographic)

Users should monitor: fasting glucose, HbA1c, IGF-1 (baseline and 4-6 weeks into dosing), PSA (men >40), and regular blood pressure. Cycling (8-16 weeks on / 4-8 weeks off) is the conservative approach although the mechanistic need for cycling is debated - unlike CJC-1295-DAC, MK-677 does not produce full somatotroph desensitization at clinical doses.