Overview
Ibutamoren mesylate (MK-677) is an orally active, non-peptidic growth hormone secretagogue that mimics ghrelin at the GHS-R1a receptor. Developed by Merck in the 1990s, it provides sustained GH and IGF-1 elevation through a convenient oral route.
Unlike synthetic GH, ibutamoren stimulates endogenous GH production, preserving pulsatile secretion and negative feedback. Clinical studies show 24-hour GH secretion increases of 55–97% and IGF-1 elevation of 40–89% across populations.
Despite extensive Phase II data, MK-677 has not received FDA approval due to concerns about insulin resistance and appetite stimulation. It remains one of the most widely studied GH secretagogues with over 30 published clinical trials.
This guide provides a comprehensive review of ibutamoren's pharmacology, clinical evidence, and safety profile.
Quick facts
- Mechanism
- Oral ghrelin receptor agonist for sustained GH/IGF-1 elevation
- Primary use
- Growth Hormone Optimization & Body Composition
- Evidence
- strong
- FDA
- Not approved
- Route
- Oral (non-peptide GH secretagogue)
- Typical results
- Sustained 40–80% increase in GH and IGF-1 levels within 1–2 weeks of daily oral dosing
Chemical information
MK-677 (C₂₇H₃₆N₄O₅S) is a gh secretagogue compound with a molecular weight of 528.67 g/mol. Its structural characteristics underpin its biological activity in growth hormone secretion.
How MK-677 works
Ibutamoren agonizes GHS-R1a in hypothalamic arcuate nucleus neurons, stimulating GHRH release and suppressing somatostatin, resulting in amplified pulsatile GH release. It also directly activates pituitary somatotrope GHS-R1a.
At the pituitary level, ibutamoren directly activates somatotrope GHS-R1a, synergizing with GHRH. It also activates appetite-regulating and sleep-promoting neurons, explaining orexigenic effects and slow-wave sleep enhancement.
Sustained IGF-1 elevation results from chronic hepatic stimulation. MK-677 increases IGF-1 without significantly altering IGF binding proteins, resulting in increased free (bioactive) IGF-1.
Ghrelin receptor activation in vagal afferents and hypothalamic feeding centers stimulates NPY/AgRP signaling, increasing appetite—therapeutically useful in cachexia but problematic for body recomposition.
- GHS-R1a agonism: Mimics ghrelin at the growth hormone secretagogue receptor
- Pulsatile GH release: Amplifies natural GH pulses preserving physiology
- IGF-1 elevation: Sustained 40–89% increase via hepatic stimulation
- Somatostatin suppression: Reduces inhibitory tone on GH release
- Sleep enhancement: Increases slow-wave sleep duration
- Appetite stimulation: Activates NPY/AgRP feeding circuits
Pharmacokinetics
| Parameter | Value | Significance |
|---|---|---|
| Bioavailability | Oral bioavailability ~60%; not significantly affected by food | Bedtime dosing recommended to minimize appetite effects and enhance sleep |
| Onset of Action | GH peak within 1–2 hours; IGF-1 over days | Time to measurable clinical/biological response |
| Half-life | ~4–6 hours; GH effects persist 8–12 hours | Determines dosing frequency |
| Duration of Effect | 24-hour GH increased with once-daily dosing | Functional activity beyond plasma clearance |
| Metabolism | Hepatic via CYP3A4; primarily fecal excretion | Primary elimination pathway |
Dosing & administration
MK-677 dosing varies by indication and individual factors. No FDA-approved dosing exists for this compound; protocols in the literature derive from limited clinical or preclinical data and practitioner experience.
Any use should be conducted under qualified medical supervision with appropriate monitoring of safety markers.
Important: These dosing ranges are not FDA-approved. Any use should be under qualified medical supervision.
Side effects & safety
Safety data for MK-677 is primarily derived from preclinical studies and limited human data. Long-term effects in humans remain incompletely characterized.
Common
- • Increased appetite (~30–50%)
- • Water retention/edema
- • Muscle pain or joint stiffness
- • Lethargy/drowsiness
- • Numbness or tingling
- • Mild fasting glucose increase
Serious / potential risks
- • Insulin resistance with chronic use
- • Potential diabetes exacerbation
- • Theoretical tumor growth risk (via IGF-1)
- • Significant edema in susceptible individuals
- • Unknown long-term cardiovascular effects
Drug interactions
| Medication | Interaction | Recommendation |
|---|---|---|
| Insulin / Sulfonylureas | MK-677 impairs insulin sensitivity; dose adjustments may be needed | Avoid combination or use with extreme caution under medical supervision |
| CYP3A4 inhibitors | May increase MK-677 plasma levels | Monitor closely; dose adjustment may be required |
| Glucocorticoids | Additive insulin resistance and fluid retention | Monitor closely; dose adjustment may be required |
| GHRH analogs | Complementary mechanisms; may amplify side effects | Generally safe; monitor if concerns arise |
Storage & handling
Oral Capsules/Tablets
- • Room temperature (20–25°C)
- • Protect from moisture/light
- • Stable 2+ years sealed
- • No special handling
Research Solution
- • Room temperature or refrigerate
- • Protect from light
- • Use within 90 days
- • DMSO or PEG-based solutions common
Cost & availability
| Source | Cost | Notes |
|---|---|---|
| Research suppliers | Varies widely | Quality and purity vary significantly between sources |
| Compounding pharmacies | Prescription required | Higher quality assurance and purity testing |
The bottom line
MK-677 is a gh secretagogue compound with research interest in growth hormone, oral gh secretagogue, body composition, sleep. While preclinical evidence is encouraging, it remains investigational and is not FDA-approved. Any use should be under qualified medical supervision.
Best for
- • Researchers studying growth hormone secretion
- • Individuals interested in growth hormone under medical guidance
Not for
- • Self-administration without medical supervision
- • Pregnant or breastfeeding individuals
- • Individuals with contraindicated conditions
Related compounds
Frequently asked questions
References
- [1] Nass R, Pezzoli SS, Oliveri MC, et al.. Effects of an oral ghrelin mimetic on body composition in healthy older adults. Ann Intern Med (2008). doi: 10.7326/0003-4819-149-9-200811040-00003 PMID: 18981485
- [2] Murphy MG, Plunkett LM, Gertz BJ, et al.. MK-677 reverses diet-induced catabolism. J Clin Endocrinol Metab (1998). doi: 10.1210/jcem.83.2.4551 PMID: 9467531
- [3] Copinschi G, Leproult R, Van Onderbergen A, et al.. MK-677 increases pulsatile GH secretion and enhances sleep quality. Neuroendocrinology (1997). doi: 10.1159/000127263 PMID: 9287078
- [4] Chapman IM, Bach MA, Van Cauter E, et al.. Daily oral MK-677 stimulates the GH-IGF-I axis in healthy elderly. J Clin Endocrinol Metab (1996). doi: 10.1210/jcem.81.12.8954023 PMID: 8954023