Melanotan II 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.
Melanotan II
Melanotan II (MT-II) is a cyclic lactam analog of alpha-melanocyte stimulating hormone (α-MSH) that acts as a potent, non-selective melanocortin receptor agonist (MC1R, MC3R, MC4R, MC5R). Developed at the University of Arizona in the late 1980s, it produces eumelanin-driven skin darkening (tanning) via MC1R, sexual arousal and spontaneous erections via MC4R, and appetite suppression via MC3R/MC4R. Bremelanotide (PT-141) — now FDA-approved for female sexual dysfunction — was derived from Melanotan II.
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| Melanotan II | MK-677 (Ibutamoren) | |
|---|---|---|
| Category | Performance & Growth Hormone | Performance & Growth Hormone |
| Also known as | MT-II, MTII, Cyclo[Nle4,D-Phe7]-α-MSH | Ibutamoren, Nutrobal, MK677, L-163,191 |
| Evidence | Research-stage | Research-stage |
| Dosing range | 250mcg–1000mcg mcg, Daily during loading phase; 2–3x weekly for maintenance | 10mg–50mg mg, once daily oral |
| Administration | Subcutaneous injection (most common), Intranasal (less effective, lower bioavailability) | Oral (capsule/liquid) |
| Key side effects | Nausea (most common — especially first 30–60 minutes post-injection), Facial flushing, Spontaneous erections (males — often unwanted at higher doses), Fatigue / yawning post-injection | Water retention, Increased appetite, Elevated fasting glucose (long-term), Fatigue (initial, transient) |
| Cited sources | 3 references | 2 references |
Key differences
- Administration: Melanotan II — Subcutaneous injection (most common), Intranasal (less effective, lower bioavailability); MK-677 (Ibutamoren) — Oral (capsule/liquid).
- Dosing units differ: Melanotan II is dosed in mcg, MK-677 (Ibutamoren) in mg — they operate at different scales.
- Frequency: Melanotan II is typically Daily during loading phase; 2–3x weekly for maintenance; MK-677 (Ibutamoren) is once daily oral.
- Research depth: this profile cites 3 sources for Melanotan II vs 2 for MK-677 (Ibutamoren).
How each works
Melanotan II
Melanotan II's broad melanocortin receptor agonism produces a constellation of effects across multiple systems. MC1R activation in melanocytes upregulates tyrosinase, the rate-limiting enzyme in melanin synthesis, producing UV-independent skin darkening. MC4R activation in the CNS and spinal cord drives sexual arousal and erectogenic effects more potent than most PDE5 inhibitors, and also produces appetite suppression and reduced food intake (the same pathway exploited by weight-loss drugs targeting the melanocortin system). MC3R activation contributes to energy homeostasis 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.