MK-677 (Ibutamoren)
unknown riskAlso: Ibutamoren · MK-0677 · L-163,191
MK-677 (ibutamoren) is the only orally bioavailable non-peptide GH secretagogue. By mimicking ghrelin's action at GHSR, it produces sustained GH and IGF-1 elevation from once-daily oral dosing — a convenience advantage that drives significant off-label and grey-market use.
Reported Benefits
GH/IGF-1 Elevation
Multiple human studies confirm sustained GH and IGF-1 increase with oral dosing.
Muscle Mass (Elderly)
Studies in frail elderly show lean mass preservation and improvement.
Bone Density
IGF-1 elevation associated with improved bone density markers.
Mechanism of Action
MK-677 is a non-peptide ghrelin receptor mimetic (GHSR agonist) with oral bioavailability (~7%). It stimulates pulsatile GH release from the pituitary through ghrelin receptor activation, leading to IGF-1 elevation. Unlike peptide GHRPs, its oral stability allows once-daily dosing.
Key Clinical Studies
Nass R et al. (2008)
RCT · 65 older adults
Increased GH and IGF-1 with lean mass improvements over 2 years
Svensson J et al. (1998)
crossover · 24 adults
MK-677 sustains GH/IGF-1 elevation for 24h post-dose
Overview
MK-677 (ibutamoren) occupies a unique position: it is technically not a peptide (it’s a small molecule GHSR agonist) but belongs pharmacologically to the GH secretagogue family. Its oral bioavailability distinguishes it fundamentally from all injectable GH secretagogues, making it the most convenient GH-stimulating option.
Phase 2 Trial Data
MK-677 has completed multiple Phase 2 trials with reasonably consistent findings: sustained GH and IGF-1 elevation, improved lean mass (particularly in frail elderly), some bone density benefit, and improved sleep architecture. These are more robust findings than most other non-approved peptides, explaining continued pharmaceutical interest.
The Cancer Concern
The IGF-1 elevation produced by MK-677 raises a theoretical concern: IGF-1 is a mitogenic growth factor, and elevated IGF-1 is epidemiologically associated with some cancers. Whether the magnitude and pattern of MK-677-induced IGF-1 elevation translates to increased cancer risk is not established, but it represents a meaningful theoretical risk requiring more long-term safety data.
Market Reality
MK-677 is sold openly online as a “research chemical,” marketed heavily to bodybuilders and anti-aging seekers. The FDA has sent warning letters to companies marketing it for human use. This regulatory status creates a consumer risk landscape of uncertain product quality and standardization.
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Regulatory Status
Research OnlyNot FDA-approved; classified as a research chemical; no 503A listing; investigated by FDA for illegal marketing
Safety Profile
Side Effects
- •Increased appetite
- •Water retention
- •Transient insulin resistance
- •Fatigue
- •Lethargy
- •Potential IGF-1-driven cancer concern (theoretical)
Contraindications
- •Active malignancy
- •Diabetes/insulin resistance
- •Congestive heart failure
Drug Interactions
- •Insulin
- •Hypoglycemic agents
Primary Uses
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