Ghrelin vs MK-677 (Ibutamoren)
A neutral, side-by-side comparison of two performance & growth hormone peptides — their mechanisms, dosing ranges, administration routes, side effects, and research evidence. For research and educational purposes only.
Ghrelin
Endogenous 28-amino acid peptide secreted primarily by the stomach that functions as both the primary hunger signal and a potent growth hormone secretagogue. The n-octanoyl modification at Ser-3 (acylated form) is required for GHS-R1a receptor binding and GH-stimulating activity. Understanding ghrelin explains the mechanism behind the entire GHRP class of research peptides.
Full profileMK-677 (Ibutamoren)
Oral non-peptide growth hormone secretagogue that mimics ghrelin to stimulate GH and IGF-1 release without injection. Long half-life (~24 hours) enables once-daily oral dosing. Widely researched for body composition, sleep quality, and IGF-1 elevation.
Full profile| Ghrelin | MK-677 (Ibutamoren) | |
|---|---|---|
| Category | Performance & Growth Hormone | Performance & Growth Hormone |
| Also known as | GHRL, growth hormone-releasing peptide endogenous, ghrelinergic peptide, acyl ghrelin | Ibutamoren, Nutrobal, MK677, L-163,191 |
| Evidence | Investigational (in trials) | Research-stage |
| Dosing range | 0.5mcg/kg–2mcg/kg mcg/kg, IV or SC bolus; endogenous levels peak pre-meal | 10mg–50mg mg, once daily oral |
| Administration | Intravenous (research), Subcutaneous injection | Oral (capsule/liquid) |
| Key side effects | Appetite stimulation, Transient hyperglycemia, Water retention, GH pulse stimulation | Water retention, Increased appetite, Elevated fasting glucose (long-term), Fatigue (initial, transient) |
| Cited sources | 2 references | 2 references |
Key differences
- Evidence level differs: Ghrelin is investigational (in trials), while MK-677 (Ibutamoren) is research-stage.
- Administration: Ghrelin — Intravenous (research), Subcutaneous injection; MK-677 (Ibutamoren) — Oral (capsule/liquid).
- Dosing units differ: Ghrelin is dosed in mcg/kg, MK-677 (Ibutamoren) in mg — they operate at different scales.
- Frequency: Ghrelin is typically IV or SC bolus; endogenous levels peak pre-meal; MK-677 (Ibutamoren) is once daily oral.
How each works
Ghrelin
Ghrelin was discovered in 1999 as the endogenous ligand for the GHS-R1a receptor. Its acylated form activates GH release from the pituitary, stimulates appetite via NPY/AgRP hypothalamic neurons, and modulates energy homeostasis and fat storage. The des-acyl form (majority of circulating ghrelin) lacks GHS-R1a activity but has independent cardiovascular and cellular effects.
MK-677 (Ibutamoren)
MK-677 binds the ghrelin receptor (GHS-R1a) to stimulate pulsatile GH release and increase circulating IGF-1. Unlike peptide GHRPs it survives oral administration. Clinical trials demonstrate significant increases in GH pulsatility and IGF-1 without suppression of the endogenous GH axis, though long-term use raises glucose metabolism concerns.
This comparison aggregates public research and structured profile data for informational purposes only. It is not medical advice and does not recommend either compound for human use. Consult a qualified healthcare provider before considering any peptide.