RESEARCH MONOGRAPH · KDC-MN-078

MK-677 (Ibutamoren)

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

67/100

Orally active ghrelin mimetic that works as advertised but the long-half-life biology is more complicated than the marketing

MK-677 (ibutamoren) is Merck's orally bioavailable non-peptide ghrelin receptor agonist, developed in the mid-90s during the big GH secretagogue gold rush, and it's pharmacologically distinct from the peptide GHRPs in an important way. The half-life is long (about 24 hours), which gives sustained elevation of GH and IGF-1 rather than the pulsatile pattern you get with injectable GHRPs paired with GHRH analogs.

What we like: oral bioavailability is genuinely useful for research applications where chronic dosing matters. The Merck phase 2 and 3 trials in elderly subjects (Murphy 2001, Nass 2008) showed reproducible IGF-1 elevations of 40-90% over baseline with daily oral dosing, which is a real pharmacological effect. The compound was eventually abandoned for the sarcopenia indication because the functional gains didn't justify the IGF-1 elevation in older populations, but the basic pharmacology is solid.

What we dont like: the sustained-elevation model is biologically different from physiological GH/IGF-1 pulsing, and chronic supraphysiological IGF-1 is not a benign state. Glucose intolerance is the consistent finding (Nass and colleagues reported HbA1c elevations and fasting glucose increases in multiple trials), water retention is significant, and the joint pain that shows up in some users is consistent with cartilage IGF-1 effects. Theres also a real cortisol and prolactin elevation at higher doses, similar to other GHSR1a agonists.

The IGF-1 elevation has theoretical implications for proliferative tissue states that are worth being honest about. Were not making clinical claims, but the mechanism math means that chronic supraphysiological IGF-1 is a different signaling state than physiological IGF-1.

Sourcing has been historically messy. MK-677 is a complex small molecule (spiroindolinone scaffold) and the synthesis is non-trivial enough that purity varies considerably across vendors. Stick to suppliers that publish HPLC and mass spec, and assume anything cheap is suspect.

For research on chronic GH/IGF-1 axis elevation, MK-677 is a useful tool because of the oral route and long half-life. Just don't conflate sustained elevation with physiological signaling.

Evidence: 72
Mechanism: 80
Reliability: 75
Safety: 55
Sourcing: 60
Value: 65
Signal: 72
Staying power: 60

Plain-language summary Intrigue 72 / 100

MK-677 (Ibutamoren) is a small-molecule growth hormone releaser that mimics ghrelin. Unlike GHRPs, it is orally active because it is not a peptide. It produces sustained growth hormone elevation, increased appetite, and improved sleep, often used in research contexts as an oral GH releaser. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Orally active non-peptide ghrelin receptor agonist

A Merck-developed orally bioavailable non-peptide ghrelin receptor agonist that produces sustained GH and IGF-1 elevation in reported research dose ranges.

Abstract

MK-677 (Ibutamoren; CAS 159752-10-0; molecular formula C27H36N4O5S; molecular weight 528.66) is a non-peptide ghrelin receptor agonist developed by Merck in the 1990s. Unlike the peptide GHRPs, MK-677 is orally bioavailable and produces sustained GH and IGF-1 elevation over 24 hours in reported research dose ranges in the literature. Phase 2 trials in elderly subjects showed sustained increases in GH, IGF-1, and lean body mass over 12 to 24 month treatment periods. The compound did not advance to FDA approval; the program was deprioritized after disappointing Phase 3 results in the GHD elderly population. The compound is sold as a research chemical/dietary supplement in some markets, though FDA has issued warnings against its sale as a supplement. Pharmacokinetics: plasma half-life 4 to 6 hours; high oral bioavailability; hepatic CYP3A4 metabolism. Reported research dose ranges in the literature are 10 to 25 mg orally. Adverse events include increased appetite, water retention, and modest insulin resistance with chronic high-dose use.

Mechanism of action

Non-peptide ghrelin receptor agonist; orally bioavailable. Sustained 24-hour GH/IGF-1 elevation.

Reported research dose ranges

Reported research dose ranges in the literature span 10 to 25 mg orally.

References

Patchett AA, et al. Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. PNAS 1995.
Nass R, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults. Ann Intern Med 2008.

Read the full monograph

The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, reported research dose ranges, sourcing and quality verification, reconstitution and handling, stack interaction considerations, and a curated reference list. Available as a research-use-only PDF download.

KDC-MN-078

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

Download PDF →

FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

Kodiac sells research compounds for investigative use only.

MK-677 (Ibutamoren)

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

Quick actions

Categories

Help and policies

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

Adjacent monographs