MK-677
Oral ghrelin mimetic. Non-peptide but routinely grouped with GH peptides.
- Primary research area
- GH secretagogue
- Last updated
- Apr 21, 2026
- Reviewed by
- Peptide Examiner editorial team
What it is
MK-677 (also known as ibutamoren, nutrobal) is a small-molecule (non-peptide) ghrelin receptor agonist and growth-hormone secretagogue. It is frequently grouped with GH peptides in biohacker discussions despite being a chemically distinct small molecule, because its pharmacological function overlaps with peptide GH secretagogues like ipamorelin. It is orally bioavailable, with a meaningful half-life that supports once-daily dosing.
Mechanism of action
MK-677 binds and activates GHSR-1a, the growth hormone secretagogue receptor, mimicking ghrelin. This drives pulsatile GH release from the pituitary, which in turn elevates circulating IGF-1. Unlike peptide secretagogues, MK-677 is a small molecule that survives oral administration. Chronic administration raises both GH and IGF-1 sustainably while preserving some pulsatility.
Research history
Merck advanced MK-677 through Phase 2 and early Phase 3 development in the 2000s for age-related GH deficiency, hip fracture recovery, and sarcopenia. The hip-fracture Phase 3 trial failed to meet primary endpoints; Merck discontinued development. Post-development, peer-reviewed research has continued on MK-677's pharmacology, appetite effects (ghrelin mimicry increases food intake), and IGF-1 effects. It remains an investigational research chemical.
Current trial status
No active FDA approval pathway. Research-use-only sales common.
Regulatory status
Not FDA approved. FDA Category 2 (September 2023, under the 'Ibutamoren' name). Feb 2026 HHS proposed removal. WADA-prohibited for competitive sport. Full regulatory timeline →
Controversies and open questions
MK-677 reliably increases appetite (ghrelin mimicry), which is a drawback for users pursuing body composition goals. Sustained elevation of IGF-1 in healthy adults has the category's usual theoretical concerns. The hip-fracture Phase 3 failure suggests that boosting GH/IGF-1 pharmacologically doesn't always translate to functional outcomes, a caution for healthy-adult enthusiasts.
Further reading
Frequently asked
Is MK-677 a peptide?
No. It's a non-peptide small molecule that binds the ghrelin receptor (GHSR-1a). It's grouped with GH peptides in biohacker discussions because its pharmacological function overlaps with peptide GH secretagogues.
Why did Merck stop development?
The hip-fracture recovery Phase 3 trial failed its primary endpoint. Secondary indications (age-related GH decline, sarcopenia) weren't pursued. It remains an investigational research chemical.
What's the main side effect?
Increased appetite — ghrelin is the hunger hormone, and MK-677 mimics its effects at the same receptor. Biohackers pursuing body composition often find this counterproductive.
Is it legal to buy?
FDA Category 2 as of September 2023 (listed as 'Ibutamoren'). Not legally compoundable. Research vendors sell it under the usual RUO disclaimers. WADA-prohibited in competitive sport.