MK-677 (Ibutamoren) vs Mod-GRF(1-29)
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.
MK-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 profileMod-GRF(1-29)
Mod-GRF(1-29) is a stabilized analog of growth hormone-releasing hormone (GHRH) that spans residues 1–29 of the native peptide. Unlike CJC-1295 (which includes a Drug Affinity Complex for multi-day half-life), Mod-GRF(1-29) has a short ~30-minute active window — mimicking the natural GHRH pulse pattern. It is the preferred GHRH component for precise, pulsatile GH protocols when combined with a GHRP.
Full profile| MK-677 (Ibutamoren) | Mod-GRF(1-29) | |
|---|---|---|
| Category | Performance & Growth Hormone | Performance & Growth Hormone |
| Also known as | Ibutamoren, Nutrobal, MK677, L-163,191 | Modified GRF(1-29), CJC-1295 without DAC, Tetrasubstituted GRF, Sermorelin analog |
| Evidence | Research-stage | Research-stage |
| Dosing range | 10mg–50mg mg, once daily oral | 100mcg–200mcg mcg, 2–3x daily, co-administered with a GHRP (pre-sleep, pre-workout, and/or upon waking) |
| Administration | Oral (capsule/liquid) | Subcutaneous injection, Intramuscular injection |
| Key side effects | Water retention, Increased appetite, Elevated fasting glucose (long-term), Fatigue (initial, transient) | Water retention (mild, dose-dependent), Tingling / numbness in extremities (carpal tunnel-like at high doses), Increased appetite (via GHRP component — less with Mod-GRF alone), Flushing or warmth at injection site |
| Cited sources | 2 references | 2 references |
Key differences
- Administration: MK-677 (Ibutamoren) — Oral (capsule/liquid); Mod-GRF(1-29) — Subcutaneous injection, Intramuscular injection.
- Dosing units differ: MK-677 (Ibutamoren) is dosed in mg, Mod-GRF(1-29) in mcg — they operate at different scales.
- Frequency: MK-677 (Ibutamoren) is typically once daily oral; Mod-GRF(1-29) is 2–3x daily, co-administered with a GHRP (pre-sleep, pre-workout, and/or upon waking).
How each works
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.
Mod-GRF(1-29)
Native GHRH(1-29) is rapidly cleaved by plasma dipeptidyl peptidase IV (DPP-IV) within 2–3 minutes. Mod-GRF(1-29) incorporates four amino acid substitutions (positions 2, 8, 15, 27) that resist DPP-IV degradation, extending the half-life to approximately 30 minutes while preserving GHRH receptor binding affinity. This creates a half-life window aligned with physiological GH pulsatility, making it suitable for 2–3x daily injections that mimic natural GH release patterns.
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.