What Is IGF-1 LR3?
IGF-1 LR3 (Insulin-like Growth Factor 1 Long R3) is a synthetic analog of IGF-1 modified with an Arg-Gly-Glu (R3) substitution at position 3 and an N-terminal 13-amino-acid extension. These modifications dramatically reduce its binding affinity for IGF binding proteins (IGFBPs) — the serum proteins that normally sequester approximately 97% of IGF-1, limiting its biological activity.
Extended Activity Profile
Native IGF-1 has a half-life of approximately 10 minutes when free (not IGFBP-bound). IGF-1 LR3's reduced IGFBP affinity extends its active half-life to approximately 20–30 hours, allowing it to maintain prolonged IGF-1 receptor activation throughout the body — a research property not achievable with native IGF-1 without continuous infusion.
Muscle Research and Safety
IGF-1 receptor activation in skeletal muscle activates the PI3K/Akt/mTOR pathway (promoting protein synthesis) and stimulates satellite cell proliferation and differentiation (enabling muscle repair and growth). Because IGF-1 signaling promotes cell growth broadly, prolonged or excessive use carries potential for off-target tissue growth effects. It is a research compound only and not approved for clinical use.
Quick Reference
Member reference tables summarize the compound's research parameters.
Research Indications
Research Protocols
As reported in cited literature and research-community logs (see Research Citations below), not a personal dosing recommendation.
This member section describes parameters reported in the research literature.
Peptide Interactions
This member section summarizes reported compound interactions and evidence limitations.
Reported Research Time Points
This member section summarizes reported research time points.
Safety Notes
Included for harm-reduction awareness only, in the event this compound is encountered outside its labeled research use. Inclusion here does not imply RUO Codes endorses, recommends, or instructs human use.
This member section discusses research safety considerations and uncertainties.
Quality Indicators
Research Citations
- Rat Muscle Hypertrophy Study (Florini et al.)
Sprague-Dawley Rats | 2.5mg/kg/day | 4 weeks | 15-20% lean mass increase - Fetal Sheep Metabolic Study (Children's Hospital Colorado)
Fetal Sheep | 6.6μg/kg/h acute, 1.17μg/kg/h chronic | 90 min to 1 week | Study halted early - Pig Growth Inhibition Study
Domestic Pigs | 180μg/kg/day | 4 days | Paradoxical growth reduction - Guinea Pig Organ Study
Guinea Pigs | 120μg/day | 7 days | No overall growth, organ-specific effects - Cancer Cachexia Rat Model
Tumor-bearing Rats | 0.3mg/kg/day | 14 days | 30% lean mass preservation - Alzheimer's Mouse Model (5XFAD)
Transgenic Mice | Intranasal LR3 | 7 months | Plaque remodeling without cognitive improvement - Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice
Engel MG, Narayan S, Cui MH, 2025, J Alzheimers Dis - The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration
Dominikowski A, Rękoś Z, Olejarz M, 2026, Front Endocrinol (Lausanne)