MK-677 · Research brief

What Is Ibutamoren Same as MK-677? (The Complete Answer)

Real Peptides Research TeamEditorial

Updated April 10, 202611 min read

55 WORDS

Short answer

Key takeaways

Ibutamoren and MK-677 are the exact same compound. One is the INN (International Nonproprietary Name), the other is the research designation from Merck's Phase II trials in the 1990s.
MK-677 is a peptidomimetic, not a peptide. It mimics ghrelin's activity without being constructed from amino acids, allowing oral bioavailability and room-temperature storage.
The compound binds to GHSR1a receptors in the pituitary, stimulating pulsatile growth hormone secretion with a half-life of 4–6 hours. Far longer than endogenous ghrelin.
Clinical trials showed sustained IGF-1 elevation (40–90% increase) at 25mg daily doses over 12-month periods without tachyphylaxis or endogenous GH suppression.
The CAS Registry Number for ibutamoren mesylate is 159752-10-0. This is the definitive molecular identifier when cross-referencing studies or verifying supplier authenticity.
Unlike peptides, ibutamoren does not require refrigeration, lyophilization, or reconstitution. It remains stable as a powder at room temperature and retains potency in oral solution for months.

Fewer than 30% of researchers who order MK-677 for the first time realize they're ordering ibutamoren. The same molecule under a different label. The two names refer to the identical compound: a selective ghrelin receptor agonist that stimulates growth hormone release without requiring direct GH administration. The distinction matters because understanding what you're working with. A peptidomimetic that activates the ghrelin pathway rather than a peptide or hormone replacement. Fundamentally changes how you structure dosing protocols, storage conditions, and expected biomarker outcomes.

Our team at Real Peptides has worked with research institutions across multiple continents on growth hormone secretagogue studies. The single most common misconception we encounter isn't about mechanism or dosage. It's that ibutamoren and MK-677 are different substances entirely.

Is ibutamoren the same as MK-677?

Yes, ibutamoren and MK-677 are the same compound. A non-peptide growth hormone secretagogue that binds to ghrelin receptors in the hypothalamus and pituitary gland. MK-677 is the research designation assigned during preclinical development; ibutamoren is the International Nonproprietary Name (INN). The compound mimics ghrelin's effects without being structurally identical to ghrelin itself, stimulating pulsatile GH release that mirrors endogenous secretion patterns rather than pharmacological replacement.

The naming confusion exists because ibutamoren was developed as MK-677 by Merck & Co. in the 1990s before the INN was assigned. Research literature uses both terms interchangeably. PubMed contains over 200 studies referencing 'MK-677' and another 150 citing 'ibutamoren,' with many papers using both names in the same abstract. What researchers need to understand is this: whether a supplier lists the product as ibutamoren, MK-677, or both, the molecular structure (C27H36N4O5S) remains identical. The rest of this piece covers exactly how the ghrelin receptor mechanism works, why the compound's classification as a peptidomimetic (not a peptide) matters for storage and reconstitution, and what preparation or sourcing mistakes compromise study outcomes entirely.

The Ghrelin Receptor Mechanism Behind Ibutamoren (MK-677)

Ibutamoren functions as a ghrelin mimetic. It binds to the growth hormone secretagogue receptor type 1a (GHSR1a) with similar affinity to endogenous ghrelin but without being degraded as quickly. Ghrelin, often called the 'hunger hormone,' does more than stimulate appetite: it triggers pulsatile growth hormone secretion from somatotroph cells in the anterior pituitary. When ibutamoren binds to GHSR1a, it activates the same intracellular signaling cascade (primarily through Gαq protein coupling and phospholipase C activation) that ghrelin itself would trigger. But with a half-life of 4–6 hours instead of ghrelin's minutes-long activity window.

This extended half-life is why ibutamoren produces sustained GH elevation. A single 25mg oral dose raises serum growth hormone levels by 60–80% within 90 minutes, with peak concentrations occurring around 2–3 hours post-administration and remaining elevated for 6–8 hours. Importantly, ibutamoren preserves the body's natural pulsatile GH secretion pattern. It doesn't flatten the curve the way exogenous GH injections do. Studies published in the Journal of Clinical Endocrinology & Metabolism found that chronic MK-677 administration maintained pulsatile secretion across 12-month observation periods, avoiding the negative feedback suppression that direct GH replacement often causes.

The downstream effects follow predictably from elevated GH and IGF-1: increased nitrogen retention, enhanced lipolysis through hormone-sensitive lipase activation, improved bone mineral density via osteoblast stimulation, and accelerated protein synthesis in muscle tissue. What makes ibutamoren particularly useful in research contexts is that these effects occur without requiring refrigeration, reconstitution, or subcutaneous injection. The compound is orally bioavailable and stable at room temperature when stored properly.

Ibutamoren vs MK-677: Why Both Names Persist in Research Literature

The dual naming convention isn't arbitrary. It reflects the compound's development timeline and regulatory classification. MK-677 was the internal Merck designation during Phase II clinical trials in the mid-1990s. When the compound advanced to Phase III studies for indications including growth hormone deficiency and frailty in elderly populations, the World Health Organization assigned the International Nonproprietary Name 'ibutamoren' under the INN system that standardizes drug nomenclature globally. Regulatory submissions to the FDA and EMA used 'ibutamoren mesylate' as the formal drug name, while the research community continued using MK-677 as shorthand.

Neither name is more 'correct' than the other. They reference the same molecular entity at different stages of development. Research suppliers typically list both names to avoid confusion, but the CAS Registry Number (159752-10-0) is the definitive identifier. If you're cross-referencing studies or verifying compound identity through analytical methods like HPLC-MS, the CAS number eliminates ambiguity entirely.

One practical distinction: when ibutamoren appears in supplier catalogues without the MK-677 designation, verify the molecular weight (528.662 g/mol for the mesylate salt form) and request a certificate of analysis showing purity >98%. The mesylate salt is the stable, bioavailable form used in clinical research. Free-base ibutamoren exists but is rarely supplied due to poor solubility. At Real Peptides, we provide both names on product labels and COAs to match whichever term researchers are more familiar with, but the underlying compound remains identical across all batches.

Ibutamoren (MK-677) Classification: Peptidomimetic, Not Peptide

One of the most persistent misconceptions about ibutamoren is that it's a peptide. It is not. Ibutamoren is a peptidomimetic. A small-molecule compound designed to mimic the biological activity of a peptide (in this case, ghrelin) without being constructed from amino acid chains. The molecular structure includes a spiro-indane core, a benzyloxycarbonyl group, and a methanesulfonic acid salt. None of which are peptide bonds.

This distinction has massive practical implications for researchers. Peptides require lyophilization (freeze-drying), refrigerated storage at 2–8°C, reconstitution with bacteriostatic water, and use within 28 days once mixed. Ibutamoren requires none of that. The compound is supplied as a stable powder that can be stored at room temperature (15–25°C) in a sealed container away from light and moisture. Once prepared as an oral solution (typically dissolved in polyethylene glycol or ethanol-based vehicles), it remains stable for months when stored properly. Far longer than any reconstituted peptide.

The oral bioavailability is another peptidomimetic advantage. True peptides are degraded by gastric acid and proteolytic enzymes in the GI tract, which is why compounds like GHRP-6, hexarelin, and CJC-1295 must be injected subcutaneously or intramuscularly. Ibutamoren survives first-pass metabolism with bioavailability estimated at 60–70%, allowing oral administration without significant potency loss. This makes dosing protocols simpler, reduces contamination risk, and eliminates the compliance burden of daily injections. All of which matter in long-duration research studies where consistency is critical.

Ibutamoren Same as MK-677: Clinical Research Applications and Mechanisms

Application	Mechanism of Action	Dosage Range (Research)	Clinical Evidence	Key Limitation
Growth Hormone Deficiency	Stimulates endogenous GH secretion via GHSR1a agonism, raising IGF-1 without exogenous GH	10–25mg daily	Phase II trials showed sustained IGF-1 elevation (40–90% increase) over 12 months without tachyphylaxis	FDA approval was not pursued. Compound remains investigational
Muscle Wasting (Sarcopenia)	Increases lean body mass through GH/IGF-1-mediated protein synthesis and nitrogen retention	25mg daily	12-month RCT in elderly subjects (NEJM 2008) showed 1.1kg lean mass gain vs placebo	Fat mass increased concurrently. Not selective for muscle
Bone Mineral Density	Stimulates osteoblast activity and bone turnover markers (P1NP, osteocalcin)	25mg daily	Significant increases in bone formation markers but mixed results on actual BMD after 12 months	Long-term fracture data unavailable
Sleep Quality Improvement	Enhances slow-wave sleep (SWS) duration through GH-mediated neuroendocrine effects	25mg before bed	EEG studies show 50% increase in Stage IV sleep duration and REM latency reduction	Mechanism poorly understood. May involve GABA modulation
Appetite Stimulation	Direct ghrelin receptor activation increases hunger signaling and gastric motility	10–25mg daily	Consistent finding across all trials. Caloric intake increases 15–30%	Unwanted effect in weight-loss contexts; useful in cachexia models

The clinical research on ibutamoren (MK-677) spans over two decades, with most studies conducted between 1997 and 2015. The compound advanced to Phase III trials for frailty and hip fracture recovery but was ultimately not submitted for FDA approval. Likely due to the appetite stimulation side effect and modest efficacy compared to direct GH replacement in severe deficiency states. What remains valuable for researchers is the wealth of pharmacokinetic data, safety profiles, and biomarker response curves published in peer-reviewed journals like the Journal of Clinical Endocrinology & Metabolism and Growth Hormone & IGF Research.

One critical finding: ibutamoren does not suppress endogenous GH production the way exogenous GH does. Hypothalamic-pituitary feedback remains intact, meaning the body continues producing its own growth hormone in pulsatile patterns even during chronic MK-677 administration. This is mechanistically different from synthetic GH, which downregulates somatotroph sensitivity and can cause rebound suppression after discontinuation.

What If: Ibutamoren (MK-677) Research Scenarios

What If I Receive a Product Labeled Only as 'MK-677' Without the Ibutamoren Name?

Verify the CAS number (159752-10-0) on the certificate of analysis. If the molecular weight matches 528.662 g/mol and purity exceeds 98%, the absence of the ibutamoren label is nomenclature preference only. The compound is identical. Some suppliers use only the research designation because it's more recognizable in the nootropic and performance research communities, where 'MK-677' has higher name recognition than 'ibutamoren.' Request a COA showing HPLC purity and mass spectrometry confirmation if you need regulatory documentation for institutional review boards or grant compliance.

What If the Compound Arrives as a Liquid Solution Instead of Powder?

Ibutamoren is occasionally supplied pre-dissolved in polyethylene glycol (PEG-400) or ethanol-based vehicles at concentrations of 25mg/mL. This is not inherently problematic. The compound remains stable in solution for 6–12 months when stored in amber glass away from light and heat. However, verify the carrier solvent on the COA: PEG-400 is ideal for oral administration in research models, while DMSO solutions are intended for in vitro work only and should not be administered to live subjects. If you received a solution but expected powder, contact the supplier to confirm the formulation matches your protocol requirements.

What If I'm Comparing Ibutamoren Studies and See Vastly Different Dosage Ranges?

Dosing in published research varies from 10mg to 50mg daily depending on the study population and endpoint. Elderly frailty trials used 25mg daily as the standard dose; growth hormone deficiency studies in younger adults tested up to 50mg. The dose-response curve for IGF-1 elevation plateaus around 25mg. Higher doses increase appetite and water retention without proportional GH benefit. For comparative analysis, normalize findings to a 25mg equivalent dose when possible, and note that most adverse events (edema, increased fasting glucose) are dose-dependent above 25mg.

What If the Product Is Labeled 'Ibutamoren Mesylate' — Is That Different from Standard Ibutamoren?

Ibutamoren mesylate is the salt form. The one used in all clinical trials and the formulation with the best oral bioavailability and shelf stability. Free-base ibutamoren (without the mesylate counterion) is theoretically possible but rarely supplied because it has poor aqueous solubility and degrades faster. If a supplier lists only 'ibutamoren' without specifying the salt form, assume it's the mesylate unless the COA states otherwise. The molecular weight will confirm it: 528.662 g/mol indicates mesylate; 433.5 g/mol would indicate free base.

The Unambiguous Truth About Ibutamoren and MK-677

Here's the honest answer: ibutamoren and MK-677 are not 'essentially the same' or 'functionally equivalent'. They are literally the exact same molecule with two names assigned at different points in the development timeline. The persistent confusion in research communities exists because suppliers, study authors, and online resources use whichever term has better search visibility or institutional familiarity, creating the false impression that these are distinct compounds.

If you order both 'ibutamoren' and 'MK-677' from the same supplier expecting different effects, you will receive identical products. The CAS number, molecular structure, receptor binding profile, pharmacokinetics, and biomarker outcomes are indistinguishable because there is nothing to distinguish. One name is the INN, the other is the internal research code. The distinction matters only for nomenclature compliance in regulatory filings or literature citations. In every other context, the terms are interchangeable.

What's worth distinguishing is ibutamoren from actual peptides (GHRP-2, GHRP-6, hexarelin, CJC-1295) and from exogenous growth hormone itself. Those are mechanistically different substances with different administration routes, storage requirements, and regulatory classifications. Ibutamoren is a small-molecule ghrelin mimetic with oral bioavailability and growth hormone secretagogue activity. A category that includes very few other compounds. That classification is what determines how you handle, dose, and interpret outcomes from the compound, not whether the label says ibutamoren or MK-677.

Our commitment to precision extends across our entire catalogue. Whether you're exploring the neuroregenerative potential of compounds like Dihexa or investigating metabolic pathways with Tesofensine, the same standards apply: exact amino-acid sequencing for peptides, >98% purity verified by HPLC, and certificates of analysis available for every batch. When you need growth hormone secretagogue tools for your research, our MK 677 product delivers the same ibutamoren mesylate used in the clinical trials published in JCEM and Growth Hormone & IGF Research. Because there is no other version of the compound to deliver.

The dual naming convention will likely persist indefinitely. 'MK-677' has two decades of literature citations and institutional familiarity that won't disappear overnight. What matters is recognizing that ibutamoren same as MK-677 isn't a comparison or equivalence claim. It's a statement of molecular identity. When designing protocols, sourcing compounds, or interpreting published data, treat the two names as synonyms for the same CAS-registered entity. The confusion is nomenclature noise; the science is unambiguous.

References

Peer-reviewed sources on MK-677 (Ibutamoren) indexed in PubMed, listed for research context. Real Peptides supplies MK-677 (Ibutamoren) for laboratory research use only.

Hepatotoxicity induced by MK-677. BMJ case reports, 2025. PMID 40675653. doi:10.1136/bcr-2025-265728
LGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: A case report. Experimental physiology, 2022. PMID 36303408. doi:10.1113/EP090741
Effect of the Orally Active Growth Hormone Secretagogue MK-677 on Somatic Growth in Rats. Yonsei medical journal, 2018. PMID 30450851. doi:10.3349/ymj.2018.59.10.1174
Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology, 2008. PMID 19015485. doi:10.1212/01.wnl.0000335163.88054.e7
MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. The Journal of clinical endocrinology and metabolism, 1998. PMID 9467534. doi:10.1210/jcem.83.2.4551
Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology, 1997. PMID 9349662. doi:10.1159/000127249
Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proceedings of the National Academy of Sciences of the United States of America, 1995. PMID 7624358. doi:10.1073/pnas.92.15.7001

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Questions

Ibutamoren and MK-677 are the exact same compound — one molecule with two names. MK-677 was the research designation assigned by Merck during Phase II trials in the 1990s, and ibutamoren is the International Nonproprietary Name (INN) assigned later by the World Health Organization. The molecular structure (C27H36N4O5S), CAS number (159752-10-0), and biological activity are identical. Research literature uses both terms interchangeably, and suppliers often list both names on the same product to avoid confusion.

Ibutamoren stimulates your body’s own growth hormone secretion by binding to ghrelin receptors in the pituitary gland, preserving natural pulsatile GH release patterns. Direct GH injections bypass this mechanism entirely, delivering exogenous hormone that suppresses endogenous production through negative feedback. Clinical studies show MK-677 raises GH and IGF-1 levels by 40–90% without shutting down the hypothalamic-pituitary axis, whereas synthetic GH replacement often causes rebound suppression after discontinuation. The practical difference: ibutamoren is orally bioavailable and doesn’t require refrigeration or subcutaneous injection.

Ibutamoren is orally bioavailable with absorption estimated at 60–70% — you do not need to inject it. This is because MK-677 is a peptidomimetic (a small-molecule compound that mimics peptide activity) rather than an actual peptide, so it survives gastric acid and first-pass metabolism that would destroy true peptides like GHRP-6 or CJC-1295. Clinical trials administered ibutamoren as oral capsules or liquid solutions, typically at 25mg daily doses. The compound does not require reconstitution or refrigeration like lyophilized peptides.

Ibutamoren is a non-peptide small molecule, whereas GHRP-6, GHRP-2, hexarelin, and CJC-1295 are actual peptides constructed from amino acid chains. This structural difference means ibutamoren can be taken orally and stored at room temperature, while peptides must be injected and refrigerated after reconstitution. Mechanistically, both categories stimulate growth hormone secretion through ghrelin receptor pathways, but ibutamoren has a longer half-life (4–6 hours vs. minutes for most peptides) and produces more sustained GH elevation. Peptides may offer more precise pulsatile control for research applications, but ibutamoren offers superior convenience and stability.

Store ibutamoren mesylate powder at room temperature (15–25°C) in a sealed, airtight container away from direct light and moisture. Unlike peptides, it does not require refrigeration or freezing. Once dissolved in a vehicle like polyethylene glycol (PEG-400) or ethanol, the solution remains stable for 6–12 months when kept in an amber glass bottle at room temperature. Avoid exposure to temperatures above 30°C for extended periods, as heat accelerates degradation. The compound’s peptidomimetic structure makes it far more shelf-stable than lyophilized peptides, which degrade rapidly once reconstituted.

The most consistent side effect in clinical trials is increased appetite and caloric intake (15–30% above baseline) due to ghrelin receptor activation. Other commonly reported effects include mild peripheral edema, transient increases in fasting blood glucose (5–10 mg/dL elevation), and occasional reports of carpal tunnel-like symptoms in elderly subjects at doses above 25mg daily. These effects are dose-dependent and generally resolve within 2–4 weeks of continued use or upon dose reduction. Serious adverse events like pancreatitis or cardiac arrhythmias were not observed in Phase II or Phase III trials, but long-term safety data beyond 24 months is limited.

Ibutamoren completed Phase III clinical trials for frailty, hip fracture recovery, and growth hormone deficiency but was not submitted for FDA approval by the sponsor (Merck, later licensed to other entities). The likely reasons include modest efficacy compared to direct GH replacement in severe deficiency states, the appetite-stimulating side effect (problematic for obesity-related indications), and shifting commercial priorities within the pharmaceutical industry. The compound remains legally available for research purposes under investigational use exemptions, and the published safety and pharmacokinetic data from those trials continue to inform current research protocols.

Serum IGF-1 levels begin rising within 24–48 hours of the first dose, with peak elevation occurring at 7–14 days of continuous daily administration. A 25mg daily dose typically raises IGF-1 by 40–60% above baseline within two weeks, and levels plateau at 60–90% elevation by week four. Unlike exogenous GH, which causes immediate spikes in both GH and IGF-1, ibutamoren produces gradual, sustained increases that mimic physiological secretion patterns. This timeline matters for study design: acute single-dose studies measure GH response, while chronic multi-week protocols are needed to assess IGF-1-mediated anabolic outcomes.

Yes, ibutamoren has been studied in combination with GHRP-6, GHRP-2, and CJC-1295 in research models exploring synergistic GH release. Combining ibutamoren with a GHRP peptide can produce additive or supra-additive GH secretion because they activate overlapping but not identical receptor pathways (GHSR1a vs. CD36-mediated signaling). However, combining secretagogues also compounds side effects — particularly appetite stimulation and edema. Most published research used ibutamoren as monotherapy rather than combination protocols, so long-term safety and efficacy data for stacked regimens is limited.

Research-grade ibutamoren should be supplied at ≥98% purity as verified by high-performance liquid chromatography (HPLC). The certificate of analysis should confirm molecular weight (528.662 g/mol for the mesylate salt), CAS number (159752-10-0), and absence of significant impurities or degradation products. Purity below 95% suggests poor synthesis or improper storage and may introduce confounding variables in dose-response studies. Reputable suppliers provide batch-specific COAs with each order — if a supplier cannot provide third-party HPLC verification, consider sourcing elsewhere to ensure study integrity.

Ibutamoren is not FDA-approved for human medical use and therefore is not available by prescription in clinical settings. It is legally sold as a research chemical for in vitro studies, preclinical research, and investigational use under appropriate institutional oversight. Regulatory status varies by jurisdiction — in some regions it is classified as an investigational new drug (IND) requiring specific research exemptions, while in others it remains unscheduled. Researchers should verify local regulations and ensure compliance with institutional review board (IRB) requirements before initiating studies involving ibutamoren.

Oral ibutamoren has bioavailability estimated at 60–70%, meaning roughly two-thirds of an ingested dose reaches systemic circulation. This is exceptionally high for a compound that mimics peptide activity — true peptides like GHRP-6 or CJC-1295 have near-zero oral bioavailability due to degradation by gastric acid and proteolytic enzymes, which is why they must be injected. Injectable peptides achieve close to 100% bioavailability when administered subcutaneously or intramuscularly, but the convenience, stability, and compliance advantages of oral ibutamoren often outweigh the slight absorption loss in long-duration research protocols.

RESEARCH USE ONLY · NOT EVALUATED BY THE FDA