GHRP-6 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.
GHRP-6
GHRP-6 is a first-generation synthetic hexapeptide GH secretagogue that strongly stimulates pituitary GH release via ghrelin receptor activation. It is one of the oldest and most well-studied GHRPs, with a large body of research spanning more than three decades. GHRP-6 produces significant GH pulses but is notable for powerfully stimulating appetite — a side effect that can be beneficial for those in a caloric deficit or disadvantageous for those managing body composition.
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| GHRP-6 | MK-677 (Ibutamoren) | |
|---|---|---|
| Category | Performance & Growth Hormone | Performance & Growth Hormone |
| Also known as | Growth Hormone Releasing Peptide-6, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 | Ibutamoren, Nutrobal, MK677, L-163,191 |
| Evidence | Preclinical only | Research-stage |
| Dosing range | 100mcg–300mcg mcg, 1–3 times daily, on an empty stomach | 10mg–50mg mg, once daily oral |
| Administration | Subcutaneous injection, Intramuscular injection | Oral (capsule/liquid) |
| Key side effects | Strong increase in appetite (most common and notable), Elevated cortisol and prolactin at higher doses, Water retention / bloating, Fatigue at high doses | Water retention, Increased appetite, Elevated fasting glucose (long-term), Fatigue (initial, transient) |
| Cited sources | 3 references | 2 references |
Key differences
- Evidence level differs: GHRP-6 is preclinical only, while MK-677 (Ibutamoren) is research-stage.
- Administration: GHRP-6 — Subcutaneous injection, Intramuscular injection; MK-677 (Ibutamoren) — Oral (capsule/liquid).
- Dosing units differ: GHRP-6 is dosed in mcg, MK-677 (Ibutamoren) in mg — they operate at different scales.
- Frequency: GHRP-6 is typically 1–3 times daily, on an empty stomach; MK-677 (Ibutamoren) is once daily oral.
- Research depth: this profile cites 3 sources for GHRP-6 vs 2 for MK-677 (Ibutamoren).
How each works
GHRP-6
Human studies confirm GHRP-6 robustly elevates GH within 15–30 minutes of injection, with effects diminishing toward baseline within 2–3 hours. Chronic use increases baseline IGF-1. Research also indicates mild stimulation of cortisol and prolactin, particularly at higher doses. Animal models have shown potential cardioprotective, hepatoprotective, and muscle-sparing effects, though human equivalents are not established.
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.