IGF-1 LR3 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.
IGF-1 LR3
IGF-1 LR3 (Long Arg3 IGF-1) is a synthetic analogue of Insulin-like Growth Factor 1 with an amino acid substitution at position 3 and a 13-amino acid N-terminal extension. These modifications prevent binding to IGF-binding proteins (IGFBPs), dramatically extending its half-life from ~12 minutes (native IGF-1) to approximately 20–30 hours. IGF-1 LR3 is widely used in research for its ability to promote cellular growth, protein synthesis, hyperplasia, and nutrient uptake into muscle tissue.
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| IGF-1 LR3 | MK-677 (Ibutamoren) | |
|---|---|---|
| Category | Performance & Growth Hormone | Performance & Growth Hormone |
| Also known as | Insulin-like Growth Factor-1 Long R3, Long R3 IGF-1, Increlex (human equivalent) | Ibutamoren, Nutrobal, MK677, L-163,191 |
| Evidence | Research-stage | Research-stage |
| Dosing range | 20mcg–100mcg mcg, Once daily post-workout, on training days only (common protocol) | 10mg–50mg mg, once daily oral |
| Administration | Subcutaneous injection, Intramuscular injection (into the trained muscle — site-specific protocols) | Oral (capsule/liquid) |
| Key side effects | Hypoglycemia (clinically significant — monitor blood sugar carefully), Jaw and organ growth with chronic high-dose use (theoretical at research doses), Fatigue and headaches, Joint pain | Water retention, Increased appetite, Elevated fasting glucose (long-term), Fatigue (initial, transient) |
| Cited sources | 3 references | 2 references |
Key differences
- Administration: IGF-1 LR3 — Subcutaneous injection, Intramuscular injection (into the trained muscle — site-specific protocols); MK-677 (Ibutamoren) — Oral (capsule/liquid).
- Dosing units differ: IGF-1 LR3 is dosed in mcg, MK-677 (Ibutamoren) in mg — they operate at different scales.
- Frequency: IGF-1 LR3 is typically Once daily post-workout, on training days only (common protocol); MK-677 (Ibutamoren) is once daily oral.
- Research depth: this profile cites 3 sources for IGF-1 LR3 vs 2 for MK-677 (Ibutamoren).
How each works
IGF-1 LR3
In vitro and animal research establishes IGF-1 LR3 as a potent anabolic and growth-promoting agent. It activates the IGF-1 receptor (IGF-1R) and downstream PI3K/Akt and MAPK/Erk pathways, promoting skeletal muscle hypertrophy and satellite cell activation. Its extended half-life makes it far more active systemically than native IGF-1. Research also documents its role in connective tissue repair, nerve regeneration, and fat oxidation. Human research is limited — most data comes from cancer cell biology and athletic performance settings.
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.