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also known as: Ibutamoren, Nutrobal, L-163,191
Half-life: ~24 hours (oral)
MK-677 (Ibutamoren) is an orally active, non-peptide growth hormone secretagogue that mimics ghrelin by binding GHS-R1a. It produces sustained, 24-hour elevation of GH and IGF-1 with once-daily oral dosing. Despite being a small molecule (not a peptide), it is extensively included in peptide clinic protocols due to its GH-stimulating mechanism.
Mechanism of Action
Potent, selective GHS-R1a agonist (ghrelin receptor). Unlike peptide GHRPs that have short half-lives requiring injection, MK-677 is orally bioavailable and has a long half-life producing sustained 24-hour GH/IGF-1 elevation.
Nass et al. (NEJM, 1998) first published Phase 2 data showing sustained GH/IGF-1 elevation and improved lean mass in elderly subjects. Multiple subsequent studies confirm body composition and sleep benefits.
CJC-1295 (GHRH) + MK-677 (ghrelin) produces synergistic GH release at both receptor types — but monitor for excessive water retention.
MK-677 provides sustained baseline GH; injectable Ipamorelin adds pulsatile peaks.
MK-677 raises GH and IGF-1; adding IGF-LR3 further maximizes downstream anabolic signaling.
Tirzepatide induces weight loss; MK-677 counters potential muscle loss by raising GH/IGF-1.
Both are ghrelin receptor agonists — choosing MK-677 (oral) vs GHRP-2 (injectable) based on preference.
Redundant ghrelin receptor stimulation.
Both are ghrelin mimetics; using both together produces diminishing returns on the same receptor.
Use injectable peptide protocol for a cycle, then transition to MK-677 for a convenient oral maintenance period.
Storage
Store at room temperature.