MK-677 (Ibutamoren)

MK-677 (ibutamoren mesylate) is a non-peptide, orally bioavailable agonist of the growth hormone secretagogue receptor type 1a (GHSR-1a), the same G protein-coupled receptor activated by the endogenous peptide ghrelin.

Structural studies published in 2021 (Lo et al., Nature Communications) resolved the cryo-EM structure of ibutamoren bound to GHSR-1a. Ibutamoren occupies both cavity I and cavity II of the ghrelin-binding pocket via three molecular arms that mimic the first four residues of ghrelin. A phenyl group forms hydrophobic contacts with residues I178, L181, and L210; an indoline-piperidine arm makes cation-pi interactions with F286 and R102; and the base of the pocket is anchored by hydrogen bonds to D99, Q120, and R283. Receptor activation proceeds through rearrangement of a salt bridge pair (E124-R283) and an aromatic cluster (W276, F279, H280, F312), propagating conformational changes that couple to Gi proteins. Separately, activation of L-type calcium channels leading to intracellular calcium elevation and protein kinase C activation has also been described for this receptor class.

At the physiological level, GHSR-1a agonism acts at both the pituitary somatotrophs (directly stimulating GH secretion) and arcuate nucleus neurons of the hypothalamus (activating NPY/AgRP orexigenic neurons), amplifying pulsatile GH release and acting synergistically with endogenous growth hormone-releasing hormone (GHRH). The net result is sustained elevation of circulating GH and downstream hepatic IGF-1 synthesis. Unlike injected GHRH peptides or recombinant GH, MK-677 preserves the pulsatile character of GH secretion and is subject to normal feedback inhibition by somatostatin, which is considered a pharmacological advantage over exogenous GH administration.

The most comprehensive human evidence comes from a 2-year, double-blind, randomized, placebo-controlled, modified-crossover trial by Nass et al. (2008; n = 65, ages 60-81) comparing 25 mg/day oral MK-677 to placebo. MK-677 increased mean 24-hour GH secretion 1.8-fold and IGF-1 1.5-fold (both p less than 0.001), restoring levels to the range typical of young adults. Fat-free mass increased 1.1 kg with MK-677 versus a decline of 0.5 kg with placebo (p less than 0.001). Limb lean mass increased, but functional outcomes (six-minute walk, stair climbing, sit-to-stand, knee and shoulder strength) did not improve significantly. Femoral neck bone mineral density showed a small decline with MK-677 relative to placebo (p = 0.004).

An earlier crossover study by Murphy et al. (1998; n = 8, PMID 9467534) demonstrated that 25 mg/day during dietary caloric restriction raised peak GH from approximately 9 to 55.9 micrograms/L after a single dose and increased IGF-1 from 188 to 264 ng/mL at steady state.

Chapman et al. (1996; n = 32, ages 64-81) reported that 25 mg/day increased mean 24-hour GH by 97% and IGF-1 by 88% at four weeks.

A multicenter Alzheimer's disease trial (PMID 19015485; n = 563, 25 mg/day for 12 months) confirmed biological engagement: IGF-1 rose 60.1% at six weeks and 72.9% at 12 months. Despite this, MK-677 showed no clinical benefit on cognitive or functional decline, illustrating that IGF-1 elevation does not translate automatically to disease modification.

A short-term study in GH-deficient prepubertal children (Codner et al., 2001; n = 18; PMID 11452249) showed dose-dependent increases in GH, IGF-1, and IGFBP-3 at 0.8 mg/kg over seven days without adverse metabolic effects at short duration.

MK-677 has not received FDA approval for any indication. All trials have been investigational. It is classified as a prohibited substance by the World Anti-Doping Agency (WADA).

Typical dosage: 10-25 mg (daily).

The dose used consistently across published randomized controlled trials in adults is 25 mg administered orally once daily, typically in the morning in the Nass et al. trials. The 2-year trial used this dose continuously without cycling.

In the Murphy et al. dietary restriction crossover study, 25 mg/day was given for the final seven days of each two-week restriction period. Chapman et al. also used 25 mg/day; lower doses of 2 mg and 10 mg were tested but produced smaller GH and IGF-1 responses.

In GH-deficient children, doses of 0.2 mg/kg and 0.8 mg/kg per day were studied for seven-to-eight-day periods; the 0.8 mg/kg dose produced statistically significant increases in IGF-1 and IGFBP-3.

Outside of formal trials, community and anecdotal reports describe oral doses of 10-25 mg/day. Some users dose at bedtime to coincide with nocturnal GH pulsatility, though this timing has not been evaluated in controlled trials. Cycling practices (e.g., 8-16 week periods) are common in performance communities but have no clinical trial basis.

Because MK-677 elevates cortisol modestly and worsens insulin sensitivity, some clinicians monitoring off-label use suggest periodic fasting glucose and HbA1c testing. Dose reduction or discontinuation has been employed in trials when fasting hyperglycemia emerged (approximately 6% of subjects in the Alzheimer's study).

This information is drawn from published clinical research and is provided for educational and encyclopedic reference purposes only. It does not constitute medical advice, and MK-677 is not approved for human therapeutic use in the United States or most other jurisdictions.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

No published controlled clinical trial has evaluated MK-677 in combination with selective androgen receptor modulators (SARMs) or other performance-enhancing compounds. The combination strategies described below reflect anecdotal community use and should be understood as such.

In performance and bodybuilding communities, MK-677 is frequently reported in combination with SARMs such as LGD-4033 (ligandrol), RAD-140 (testolone), and ostarine (MK-2866). The stated rationale is complementary anabolic signaling: SARMs target androgen receptors in muscle and bone, while MK-677 elevates GH and IGF-1 through a distinct receptor pathway. Users anecdotally report that adding MK-677 to a SARM cycle improves recovery, sleep quality, and fat-free mass accrual.

A case report (PMC9331610) documented a 47-year-old male who developed a severe hyperglycemic crisis (initial glucose 558 mg/dL, HbA1c 13.9%) after using MK-677 25 mg/day with RAD-140 and andarine (S4) for three months. Glucose control normalized within one year of cessation, but the case illustrates that metabolic risks may be compounded when combining GH secretagogues with other unlicensed compounds.

MK-677 has also been studied alongside standard pharmacology in hypogonadal males receiving testosterone replacement therapy, where combined GHRP-class agents are sometimes used off-label, though controlled trial evidence for this combination specific to MK-677 is lacking.

MK-677 (Ibutamoren) is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

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Reported side effects: Increased appetite, water retention, elevated blood sugar, potential insulin resistance

Data from the 2-year randomized trial (Nass et al., 2008; n = 65) provide the most systematic adverse event profile. Increased appetite occurred in 67% of MK-677 subjects versus 36% on placebo; this subsided to near baseline within three months in approximately half of affected subjects. Transient lower-extremity edema occurred in 44% (vs. 27% placebo) and transient muscle pain or arthralgia in 33% (vs. 9% placebo).

Metabolically, fasting blood glucose increased an average of 0.3 mmol/L (approximately 5 mg/dL; p = 0.015) and HbA1c increased 0.2 percentage points (p = 0.002); eight subjects reached HbA1c above 6% at 12 months. Insulin sensitivity declined significantly (QUICKI index, p less than 0.001). These changes, while statistically significant, remained within ranges characterized by the trial investigators as clinically modest, but individuals with pre-existing impaired glucose tolerance or metabolic syndrome carry elevated risk.

A published case report (PMC9331610) describes frank diabetic crisis in a user combining MK-677 with multiple SARMs, underscoring the glucose risk in susceptible individuals or with polypharmacy.

Cortisol increased by approximately 47 nmol/L with MK-677 (p = 0.020). Femoral neck bone mineral density showed a small relative decline versus placebo (p = 0.004). Elevated prolactin has been reported in pharmacological studies.

A 2025 case report (PMID 40675653) documented transaminitis in a single user, with liver enzymes normalizing after cessation. Attribution to MK-677 in multi-compound products is complicated by concurrent use of other agents; the LiverTox entry for SARMs notes that MK-677-specific hepatotoxicity evidence remains scarce.

Serious adverse events in the Nass trial included one tongue adenocarcinoma and one myocardial infarction in the MK-677 group; the trial investigators could not establish causality given the small sample. MK-677 is not FDA approved, is banned by WADA, and is not recommended for use in individuals with active malignancy, diabetes mellitus, or known cardiac disease.