MK-677
MK-677 (Ibutamoren) — Oral GH Secretagogue
MK-677 (Ibutamoren) is a non-peptide, orally active ghrelin receptor agonist (GHSR-1a) that stimulates GH and IGF-1 secretion with a remarkably long half-life of approximately 24 hours. It is one of the most widely used research compounds globally due to its oral administration and once-daily dosing. Phase 2 clinical trials demonstrated significant GH/IGF-1 elevation, improved body composition, and bone mineral density increases. Its close structural mimicry of ghrelin produces the same appetite-stimulating effects as GHRP-6.
Mechanism of Action
MK-677 mimics ghrelin's binding to GHSR-1a receptors, activating the same signalling cascade that endogenous ghrelin uses to stimulate GH release. As a small non-peptide molecule, it resists enzymatic degradation and is orally bioavailable — properties unachievable for peptide GHRPs.
Due to its 24-hour half-life, once-daily dosing produces sustained GHSR-1a activation that generates continuous GH pulse amplification throughout the day and night. This produces measurably elevated IGF-1 levels within 2–4 weeks of starting.
MK-677 potently activates the appetite-stimulating pathways of the ghrelin system in addition to GH-releasing pathways — the same broad ghrelin receptor activation that causes GHRP-6's appetite effects. Caloric management is an important consideration during MK-677 protocols.
Research Evidence
MK-677 has one of the most extensive clinical datasets of any non-approved GH secretagogue, with Phase 1/2 trials across multiple populations including GH-deficient adults, elderly frail patients, and post-hip-fracture patients.
MK-677 Increases GH and IGF-1 in Healthy Elderly Adults
9-month MK-677 25mg/day in healthy elderly adults produced sustained GH and IGF-1 elevation to levels comparable to young adults, with increases in lean body mass, reduced fat mass, and improved protein turnover.
MK-677 Improves Functional Measures in Hip Fracture Recovery
MK-677 in elderly hip fracture patients improved stair climbing power, muscle strength, and functional status at 6 months versus placebo, with a significant reduction in falls.
Typical Research Protocol
Bedtime dosing reduces daytime hunger effects and aligns GH elevation with natural nocturnal pulse. 10mg is a reasonable starting dose to assess tolerance. 25mg is the most common research dose. IGF-1 monitoring is strongly recommended — MK-677 reliably elevates IGF-1 and levels should be checked at 8 weeks.
Safety Profile
Reported Side Effects
- Increased appetite (often significant)
- Water retention / oedema
- Tingling or numbness (extremities)
- Fatigue (initial weeks)
- Increased insulin resistance (especially fasting glucose)
- Joint pain at higher doses
Contraindications
- Active malignancy
- Uncontrolled diabetes (insulin resistance worsening)
- Severe fluid retention conditions (CHF, severe liver disease)
- Hypothyroidism (correct first)
- Pregnancy
Common Research Stacks
Frequently Asked Questions
Is MK-677 a SARM (Selective Androgen Receptor Modulator)?
No — MK-677 is frequently miscategorised as a SARM but has no androgen receptor activity. It is a ghrelin receptor agonist (GHSR-1a activator) that raises GH and IGF-1. The confusion arises from MK-677 being sold alongside SARMs by some research chemical vendors and its similar body composition-improving properties. Its mechanism is entirely through the GH axis, not the androgen receptor.
Does MK-677 suppress natural GH production?
Unlike exogenous GH replacement, which suppresses natural production via negative feedback, MK-677 stimulates endogenous GH release by the pituitary. Natural GH production is preserved because MK-677 acts upstream of the pituitary (via GHSR-1a) rather than bypassing it with exogenous hormone. Recovery of natural pulsatility after stopping is typically complete within 1–2 weeks.
Can MK-677 cause insulin resistance?
Yes — GH acutely antagonises insulin signalling. MK-677's sustained GH elevation produces measurable fasting glucose increases in some users, particularly at 25mg doses. This effect is dose-dependent and typically reversible. Fasting glucose and HbA1c should be monitored. Those with pre-diabetes or family history of type 2 diabetes should start at 10mg and monitor closely.
How long does it take for MK-677 to raise IGF-1?
IGF-1 elevations are typically measurable within 2–4 weeks of starting. Maximum IGF-1 response generally occurs at 4–8 weeks. In Merck's Phase 2 trials, IGF-1 levels rose to young-adult equivalents within the first month of 25mg daily use in elderly subjects.
Is MK-677 legal to purchase?
MK-677 is not FDA-approved for any indication in the US and is not a scheduled controlled substance. It exists in the same research chemical category as most peptides. Purchase as a research chemical is legal in many jurisdictions. However, it is prohibited under WADA anti-doping rules (S2 category) and athletes competing under tested sports organisations face sanctions.
What are the long-term effects of MK-677?
The longest clinical trials ran approximately 2 years in elderly populations. Long-term effects included sustained IGF-1 elevation, improved lean mass and bone mineral density, and no significant safety concerns (when excluding diabetic populations). The main long-term concern is sustained insulin resistance in susceptible individuals. A 9-month RCT in healthy elderly adults showed no serious adverse events.
Key Research References
- Nass R et al. (2008). Effects of MK-677 in growth-hormone-deficient adults. J Clin Endocrinol Metab.
- Svensson J et al. (1998). Two-month treatment of obese subjects with the oral growth hormone secretagogue MK-677. J Clin Endocrinol Metab.
- Chapman IM et al. (1996). Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by MK-677. J Clin Endocrinol Metab.
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