MK-677

MK-677 (Ibutamoren) is not a peptide; it is a non-peptide, orally active growth hormone secretagogue (GHS). While it acts similarly to peptides by stimulating the release of growth hormone (GH) and IGF-1, it is a synthetic, small-molecule drug, not a chain of amino acids like traditional peptides.

Key Benefits

• May help increase natural growth hormone and IGF-1 levels
• Commonly researched for improving muscle growth, recovery, and physical performance
• May support better sleep quality and overnight recovery processes
• Research suggests potential benefits for appetite support, bone health, and healthy aging

FDA-Approved Uses

IMPORTANT NOTE: MK-677 (Ibutamoren) is NOT a peptide. It is a non-peptide, orally active small molecule growth hormone secretagogue. It is included in this document as it is widely used alongside peptide GH secretagogues and is commonly discussed in the same clinical context.

MK-677 has never received FDA approval. A New Drug Application has not been filed. Originally developed by Merck & Co. as a potential treatment for several conditions; Phase 2 trials were completed but further development was discontinued by Merck (likely for commercial/patent reasons; not due to insurmountable safety signals).

Conditions studied in Phase 1–3 clinical trials (none FDA-approved)

• Growth hormone deficiency in adults (Phase 2 completed)
• Muscle wasting / sarcopenia in hip fracture patients (Phase 3 — did not meet primary endpoint)
• Growth failure in children with GH deficiency (Phase 2)
• Protein-energy wasting in chronic kidney disease (Phase 2 — favorable results)
• Alzheimer’s disease (Phase 2 — favorable body composition effects, not primary endpoint)
• Obesity / metabolic syndrome (Phase 2)

WADA status: Prohibited at all times under S2 — Peptide Hormones, Growth Factors, Related Substances and Mimetics
(Note: WADA prohibits it despite it not being a peptide — prohibited by functional class)

Trade Names in USA and Manufacturers

No FDA-approved trade name in the USA.

Developed by: Merck & Co. (compound code: MK-677; also known as L-163,191)
Also known as: Ibutamoren, Ibutamoren mesylate (the mesylate salt is the common research chemical form)

US availability of MK-677

• Research chemical vendors (unregulated; ‘research use only’): Most commonly available source in USA
• Compounding pharmacies: Legal status uncertain; MK-677 is not a peptide — it may not fall clearly under the 503A bulk peptide compounding framework. Verify with legal counsel and current FDA guidance.
• Some US telehealth/wellness clinics prescribe compounded capsules; legal basis varies by state

Molecular identity

• Non-peptide small molecule; indane-type compound
• MW: 624.77 g/mol (free base); 528.67 g/mol (mesylate salt)
• Molecular formula: C₂₇H₃₆N₄O₅S
• Oral bioavailability: ~60–80%
• Half-life: ~24 hours (enables once-daily oral dosing)
• Does not require injection — key differentiator from all peptide GH secretagogues

Dosage

No FDA-approved dosing. Reflects Phase 2/3 clinical trial doses and off-label practice.

Oral capsule/tablet — Once daily

• Clinical trial doses: 10 mg, 20 mg, 25 mg, 50 mg per day
• Most commonly used dose: 25 mg/day (best efficacy/tolerability balance)
• Starting dose: 10 mg/day (lower appetite stimulation, fewer side effects)
• Maximum studied dose: 50 mg/day (significantly increased side effects at this dose)

Timing

• Once daily; bedtime preferred
• Reason: Aligns with natural GH nocturnal pulse; avoids daytime appetite stimulation in social/work settings
• Some users prefer morning to manage sleep effects

Cycling

• Commonly used in cycles: 8–16 weeks on, 4–8 weeks off
• Some clinicians use low-dose (10–15 mg) for extended periods
• Reason: Limit chronic IGF-1 elevation and manage appetite/insulin resistance over time

Form: Oral capsule (most common) or liquid solution
Storage: Room temperature; stable long-term as a small molecule (unlike peptides)

Pricing

No FDA-approved commercial pricing.

Research chemical vendors (most common US source, unregulated):
25 mg capsules (30-count): ~$30–$70/month
[Significantly cheaper than injectable peptide alternatives]

Compounded capsules (503A, where legally prescribed):
~$60–$150/month depending on pharmacy and dose

Key cost advantage over injectable peptides:
MK-677 oral dosing eliminates: needles, syringes, bacteriostatic water, and sterility concerns
Monthly total cost is typically 50–70% lower than the equivalent CJC-1295/Ipamorelin injectable stack

Tips

• MK-677 is NOT a peptide — it is an oral small molecule. If you are looking for a no-injection option to boost GH/IGF-1, it is the only oral compound in this class. This is its primary practical advantage.
• WADA S2 prohibited: Do not use if subject to anti-doping testing — prohibited regardless of its non-peptide nature.
• Appetite stimulation is the most practically disruptive side effect for many users. Taking at bedtime significantly reduces the daytime appetite impact compared to morning dosing.
• Water retention (especially in the first 2–4 weeks) is common but typically self-resolves. Starting at 10 mg for the first 2 weeks significantly reduces initial water retention and appetite effects.
• Monitor fasting blood glucose and IGF-1 every 3 months during use.
• Unlike peptide GHRPs, MK-677 has long-term (24-month) human safety data from Merck’s Phase 3 hip fracture trial — this is actually a scientific advantage over most peptides.

Side Effects

From Merck Phase 2/3 clinical trials and post-market research:

Very common (dose-dependent):

• Increased appetite: Significant and consistent across all trials; most common reason for dose reduction or discontinuation
• Water retention / peripheral edema: Especially in first 2–4 weeks; usually self-resolving
• Lethargy or fatigue: Especially at higher doses (25–50 mg); often improves over time
• Numbness and tingling (paresthesia): Related to fluid retention; carpal tunnel-like symptoms
• Elevated fasting blood glucose: Consistent finding across trials; clinically significant in patients with metabolic risk factors
• Insulin resistance: Persistent concern with chronic use; distinguishes MK-677 from pulsatile peptide GH secretagogues

Less common:

• Muscle pain or joint discomfort
• Vivid dreams / altered sleep architecture (GH released during deep sleep)
• Mild prolactin elevation: Observed in some participants; generally not clinically significant at standard doses
• Lightheadedness

Rare:
Acceleration of pre-existing malignancy growth: Observed in the Phase 3 hip fracture trial (MK-677-97-5 study) — the primary endpoint (reducing falls/fractures) was not met, and increased cancer incidence in the MK-677 arm raised concerns and contributed to trial termination

Contraindications

No formal contraindications (no approved label).

Based on clinical trial data and pharmacology:
– Active malignancy or high cancer risk: Phase 3 trial raised cancer signal — contraindicated in active cancer; extreme caution in anyone with elevated cancer risk
– Diabetes mellitus or significant insulin resistance: Consistent insulin resistance worsening in trials — use with caution or avoid; monitor glucose closely
– Athletes subject to WADA/USADA: Prohibited under S2 — absolute contraindication for tested athletes
– Severe fluid retention states (congestive heart failure, nephrotic syndrome, cirrhosis): Risk of worsening edema
– Elderly patients (≥65): Hip fracture trial cancer signal was observed in an elderly population — particular caution warranted
– Pregnancy and breastfeeding: No safety data; not recommended
– Children with open epiphyses: Not recommended
– Hypersensitivity to MK-677 or formulation components
– Patients on insulin or oral hypoglycemics: MK-677 worsens insulin sensitivity — dose adjustment of diabetes medications may be required

Pharmacology

MK-677 (Ibutamoren mesylate; L-163,191) is a non-peptide, orally bioavailable, selective agonist of the ghrelin receptor (growth hormone secretagogue receptor 1a; GHSR-1a). Developed by Merck & Co. as part of a GH secretagogue program aimed at finding orally active alternatives to injectable GH and GHRH analogues. MW: 624.77 g/mol (free base); molecular formula: C₂₇H₃₆N₄O₅S. Oral bioavailability: ~60–80%. Half-life: ~24 hours — enabling once-daily dosing and sustained 24-hour GH/IGF-1 elevation. This is fundamentally different from injectable GHRH analogues (CJC-1295) and GHRPs (Ipamorelin), which produce transient physiological GH pulses. MK-677’s prolonged action creates a non-pulsatile, continuous GH elevation pattern — more similar in some ways to exogenous GH than to natural pulsatile release.

Mechanism of action

MK-677 selectively binds to and activates GHSR-1a (ghrelin receptor / growth hormone secretagogue receptor 1a) on pituitary somatotroph cells and in the hypothalamus:

1. Pituitary GHSR-1a activation:
→ Stimulates GH synthesis and release from anterior pituitary
→ Produces sustained (~24h) elevation of GH levels
→ GH then stimulates hepatic and peripheral IGF-1 production

2. Hypothalamic effects:
→ Activates GHSR-1a in the arcuate nucleus and other hypothalamic regions
→ Stimulates orexigenic (appetite-promoting) neuropeptides (NPY, AgRP)
→ EXPLAINS the significant appetite stimulation — same pathway as ghrelin (‘hunger hormone’)

3. Peripheral GHSR-1a:
→ Some peripheral effects on fat tissue, bone, and other tissues via direct receptor activation independent of pituitary GH

Key pharmacological distinction from peptide GHRPs:
– MK-677’s 24-hour half-life produces CONTINUOUS GH elevation (not pulsatile)
– Pulsatile GH (from injectable CJC-1295/Ipamorelin) allows insulin sensitivity to normalize between pulses
– MK-677’s continuous GH pressure maintains chronic insulin resistance — the primary metabolic disadvantage

GH and IGF-1 downstream effects: Protein synthesis, lipolysis, lean mass maintenance, bone turnover, IGF-1-dependent anabolic signaling

Result Claims By Different Companies

Merck & Co. (based on completed Phase 2/3 clinical trials — drug never commercialized):

Growth Hormone Deficiency adults (Svensson et al., J Clin Endocrinol Metab, 1998):
– Statistically significant increases in GH and IGF-1 levels
– Improvements in body composition: increased lean mass, reduced fat mass
– Generally well-tolerated at 25 mg/day

Phase 2 — Protein-energy wasting in CKD (Chapman et al., Kidney International, 1996):
– Significantly increased IGF-1 levels in CKD patients
– Positive effects on nitrogen balance and lean body mass

Phase 3 — Hip fracture trial (Murphy et al., J Clin Endocrinol Metab, 1999; MK-677-97-5 study):
– Did NOT meet primary endpoint (reduction in falls/fractures in elderly patients)
– Increased IGF-1 and lean mass confirmed
– ⚠️ Increased cancer-related adverse events observed in MK-677 arm vs. placebo in elderly population
– Study termination contributed to Merck discontinuing further development

Alzheimer’s / cognitive aging (Sevigny et al., Neurology, 2008):
– Improved body composition endpoints in MCI/Alzheimer’s patients
– Primary cognitive endpoints not met

⚠️ Important: Despite promising body composition and IGF-1 data, MK-677 has not been FDA-approved. The Phase 3 cancer signal in elderly patients is a significant safety consideration that should be weighed against any potential benefits.

Disclaimer

This content about “MK-677” is for informational and educational purposes only, is not medical advice, does not replace consultation with a licensed healthcare professional, and affiliate links may result in compensation at no additional cost to you.