From Justin · PEDs & Compounds
Ibutamoren monograph
Justin Harris — IFBB Pro Coach
From Justin
MK-677 (ibutamoren) is an oral ghrelin-receptor agonist. It makes the pituitary push more pulsatile GH, which raises IGF-1 downstream. It is not injected GH and it is not a direct GH-receptor drug. The usual tradeoffs are hunger, water retention, and worse insulin sensitivity. The hunger and water retention can be helpful, especially for strength — but it's not generally worth the effects on insulin sensitivity. Half-life is roughly a day, so once-daily dosing is what the pharmacology supports. It is not FDA-approved, and athletes should treat it as doping-relevant until they check the current list. In a narrow use-case, it has value.
Overview
Ibutamoren is an investigational oral growth hormone secretagogue that increases pulsatile GH release and downstream IGF-1. It has been studied for growth hormone deficiency, catabolic states, and body-composition endpoints, but it is not an approved drug in routine clinical practice. Human evidence is real but limited, and most bodybuilding use is off-label, experimental, or anecdotal.[^1]
Pharmacokinetics & Mechanism
- Class: Orally active nonpeptide growth hormone secretagogue; ghrelin receptor (GHSR) agonist
- Mechanism of action: Ibutamoren is a nonpeptide agonist of the ghrelin receptor (GHSR/GHSR-1a) that stimulates growth hormone secretion from the pituitary and hypothalamic GH axis. Structural work shows it binds the human ghrelin receptor and activates GHSR signaling; review literature notes it promotes pulsatile GH release subject to negative feedback, which may reduce the risk of sustained supraphysiologic GH levels compared with direct GH exposure.
- Target(s): Primary target: ghrelin receptor (GHSR/GHSR-1a), a GPCR. Downstream pathway: hypothalamic/pituitary growth-hormone secretagogue signaling with increased GH pulse amplitude and increased hepatic IGF-1 production. It is not a direct GH receptor agonist.
- Route(s) of administration: Oral only in human studies and in common use. Not a peptide injection product; no reconstitution applies for standard ibutamoren tablets/capsules.
- Onset: Not well established for a single subjective onset. In trials, endocrine changes in GH/IGF-1 were observed within days; appetite may increase earlier, but precise onset in humans is not well established.
- Half-life: Commonly reported human half-life is about 24 hours (often cited roughly 24–30 hours), supporting once-daily dosing. I did not find a credible primary source in this pass that stated an extended/depot/DAC variant for ibutamoren; no DAC variant is established for MK-677 itself.
- Metabolism / clearance: Human metabolic pathway details are not well established in the sources reviewed here. Published work notes metabolite characterization in animals and doping-control contexts; clearance appears to be non-peptide oral small-molecule handling rather than renal peptide clearance. Exact dominant CYP/UGT pathways and elimination fractions are not well established from the sources checked.
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