MK-677, known in the scientific literature as Ibutamoren or by its development designation MK-0677, is a non-peptide ghrelin mimetic and orally active growth hormone secretagogue. Unlike the injectable GHRP peptides from which it is conceptually derived, MK-677 demonstrates oral bioavailability in animal and human research models — a property that has made it a practical tool compound in studies examining the growth hormone/IGF-1 axis, body composition, and metabolic physiology. It was originally developed by Merck and has been evaluated in multiple Phase II and Phase III clinical trials.
For researchers investigating growth hormone secretion dynamics, the ghrelin receptor system, or the downstream effects of sustained GH/IGF-1 elevation on body composition, bone metabolism, and sleep architecture, MK-677 represents one of the most extensively characterized oral GH secretagogues in the preclinical and clinical literature.
MK-677 is a small molecule agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a) — also known as the ghrelin receptor. Unlike peptide-based secretagogues such as GHRP-2 or Ipamorelin, which require parenteral administration due to poor oral bioavailability, MK-677 is a non-peptide compound designed for oral activity. It mimics the action of ghrelin, the endogenous GHS-R1a ligand, stimulating growth hormone release from the anterior pituitary without the requirement for prior GHRH priming that characterizes some other secretagogues.
MK-677 was synthesized as part of a systematic effort to develop orally bioavailable growth hormone secretagogues, first described in the literature in the mid-1990s. Its development contributed significantly to the understanding of the ghrelin receptor system and established proof of concept for non-peptide GH secretagogue pharmacology. The compound is supplied as a white crystalline powder and is stable at room temperature in dry conditions — a handling characteristic that distinguishes it from most injectable research peptides.
| Property | Value |
|---|---|
| Full name | Ibutamoren mesylate (MK-677) |
| Also known as | MK-0677, L-163,191, Ibutamoren |
| Molecular formula | C₂₇H₃₆N₄O₅S (free base) |
| Molecular weight | 528.66 g/mol (free base) |
| CAS number | 159634-47-6 |
| Purity (Official Peptides) | >99% by HPLC |
| Physical form | White to off-white crystalline powder |
| Solubility | DMSO, ethanol; limited aqueous solubility |
| Half-life (research models) | ~24 hours (oral administration) |
| Storage | Room temperature, dry, sealed; stable 2+ years |
MK-677’s primary pharmacological activity — GHS-R1a agonism — produces dose-dependent increases in growth hormone pulse amplitude and IGF-1 levels in research models. Early clinical pharmacology studies established that oral MK-677 produces sustained elevations of mean 24-hour GH secretion and serum IGF-1 concentrations without the tachyphylaxis observed with some injectable GHRPs.
Research has characterized MK-677’s effects on GH pulsatility in detail. Unlike continuous GH infusion, which suppresses endogenous GH secretion through negative feedback, MK-677 amplifies pulsatile GH release — preserving the physiological pattern of GH secretion while increasing total GH output. This mechanism is considered more physiologically relevant by researchers studying GH axis function compared to exogenous GH administration, which bypasses endogenous secretory control entirely.
Studies examining IGF-1 responses to MK-677 have documented dose-dependent IGF-1 elevation that persists for the duration of treatment in animal models. Research designs examining GH deficiency models have used MK-677 as a tool to restore GH/IGF-1 axis activity to physiological ranges without exogenous GH administration — providing a useful experimental approach for isolating GH axis-dependent effects from GH receptor-independent effects.
The metabolic consequences of sustained GH/IGF-1 elevation through MK-677 administration have been extensively examined in both preclinical and clinical research settings. Studies in healthy adults and GH-deficient subjects have documented measurable effects on body composition including lean mass accretion and changes in fat distribution over 8–24 week treatment periods.
Research examining MK-677 in elderly subjects has been particularly notable. A 2-year randomized controlled trial in men and women over 60 years old documented sustained IGF-1 elevation and significant increases in fat-free mass compared to placebo. Importantly, the same study reported no significant improvement in functional outcomes, highlighting the distinction between surrogate markers (IGF-1, lean mass) and clinical endpoints — a distinction of direct relevance to researchers designing functional outcome studies.
Studies in catabolic states have examined MK-677’s potential to attenuate diet-induced muscle protein catabolism. Research in healthy adults undergoing caloric restriction documented preservation of lean mass in MK-677-treated groups compared to controls, with no requirement for exercise intervention — a finding relevant to researchers studying muscle wasting and protein metabolism.
One of the most consistently documented non-metabolic effects of MK-677 in research is its impact on sleep architecture. Multiple studies have reported that MK-677 administration significantly increases slow-wave sleep (SWS) duration — the deep, restorative sleep phase during which the majority of endogenous GH secretion occurs in a physiological context.
A double-blind crossover study in young adults documented a 50% increase in SWS duration following MK-677 administration, with concurrent increases in overnight GH secretory activity. Research in elderly subjects has similarly reported MK-677-associated increases in REM sleep percentage and SWS duration. These sleep effects are considered mechanistically related to ghrelin’s documented role in sleep regulation via GHS-R1a signaling in hypothalamic nuclei involved in sleep-wake cycle control.
The GH/IGF-1 axis plays a well-established role in bone formation and mineral metabolism, and research has examined MK-677’s effects on bone turnover markers and bone mineral density in relevant model systems. Studies measuring bone formation markers — including osteocalcin and bone alkaline phosphatase — have reported significant increases in MK-677-treated groups, consistent with GH-driven stimulation of osteoblast activity.
A 2-year study in obese subjects documented significant increases in bone mineral density at the femoral neck in MK-677-treated groups compared to placebo, alongside improvements in whole-body BMD measurements. Research in hip fracture patients has also examined whether MK-677’s anabolic effects on bone metabolism translate to functional outcomes in fracture healing — an area of particular clinical research interest.
More recent research has examined MK-677 in the context of cognitive function and neurological health. The IGF-1 axis has documented effects on neuronal survival, synaptic plasticity, and myelination, and researchers have used MK-677 as a tool to examine whether GH/IGF-1 axis restoration affects cognitive parameters in GH-deficient and elderly models.
Studies in elderly subjects have examined MK-677’s effects on measures of cognitive performance, with particular interest in whether IGF-1 restoration can attenuate age-related cognitive decline. Research has also examined the compound in the context of neurodegenerative disease models, where IGF-1 signaling deficits have been proposed as contributing factors.
MK-677’s mechanism operates through GHS-R1a — the ghrelin receptor — which is expressed not only in the pituitary and hypothalamus but throughout the body including cardiac tissue, immune cells, adipose tissue, and the gastrointestinal tract. This broad receptor distribution means that MK-677’s effects are not limited to GH secretion but extend to all tissues where GHS-R1a signaling is physiologically active.
Ghrelin itself is a 28-amino acid acylated peptide produced primarily in the gastric fundus, and its GHS-R1a agonism integrates metabolic status with endocrine signaling — linking nutritional state to GH release. MK-677’s oral bioavailability allows it to occupy the ghrelin receptor in the context of normal feeding behavior, making it useful in research designs examining ghrelin receptor biology without the confounding effects of acute ghrelin injection on appetite and gastric motility.
Research examining MK-677’s GHS-R1a binding kinetics has characterized it as a high-affinity full agonist with a binding profile distinct from peptide GHRPs. This non-peptide structure provides greater proteolytic stability and allows oral delivery, but also means that receptor selectivity profiles must be characterized independently of peptide GHRP data — a consideration for researchers interpreting GHS-R1a biology from MK-677 studies.
MK-677’s non-peptide structure confers significantly greater chemical stability than injectable peptide secretagogues. The compound is stable at room temperature in dry conditions for extended periods — a practical advantage for laboratory inventory management.
Solubility considerations: MK-677 has limited aqueous solubility. For in vitro work, stock solutions are typically prepared in DMSO at 10–50 mM concentration and diluted in aqueous medium immediately before use. DMSO concentration in final working solutions should be kept below 0.1% to avoid solvent-mediated cytotoxicity in cell-based assays.
Appetite stimulation in animal models: MK-677’s ghrelin receptor agonism stimulates appetite in rodent models. Researchers designing body composition or metabolic studies with MK-677 should control for food intake differences between treated and control groups, or use pair-feeding designs to isolate direct metabolic effects from secondary effects of increased food consumption.
Insulin sensitivity effects: MK-677 can reduce insulin sensitivity in some research subjects, consistent with the well-established GH-induced insulin antagonism. Studies examining metabolic endpoints should include appropriate insulin sensitivity measurements and consider this effect when interpreting body composition or glucose metabolism data.
Concentration and dose selection: Published research spans a wide dose range in both animal and human studies. Review relevant literature for your specific model system before designing dose-response experiments, as effective concentration ranges differ significantly between in vitro, rodent, and primate models.
Official Peptides supplies MK-677 at >99% purity verified by HPLC and mass spectrometry. Each batch is accompanied by a certificate of analysis from an independent third-party laboratory confirming compound identity, purity, and molecular weight. We maintain consistent US-based inventory with same-day dispatch on qualifying orders.
MK-677 is available from Official Peptides in powder form suitable for dissolution in DMSO or ethanol for stock preparation. For research programs requiring ongoing supply, contact our team to discuss volume availability.
All content is provided for research reference purposes only. For in vitro laboratory research use only.