IGF-1 LR3
IGF-1 LR3 is a laboratory-engineered, long-acting analogue of insulin-like growth factor-1 that binds IGF-binding proteins far more weakly than native IGF-1, prolonging its bioactive presence in animal models, but it has not been tested in controlled human clinical trials.
This page is a research-orientation summary, not a dosing guide. For anything beyond general background, read the primary literature or talk to a qualified clinician — specifics like amount, frequency, or administration aren't something we publish here.
What it does & how it works
IGF-1 LR3 is a recombinant analogue of human IGF-1 created by substituting arginine for glutamic acid at position 3 and adding a 13-amino-acid extension at the N-terminus. These modifications sharply reduce its affinity for IGF-binding proteins (IGFBPs) while preserving binding to the type 1 IGF receptor (IGF-1R), so a larger fraction of the administered molecule remains 'free' and receptor-available compared with native IGF-1. Like native IGF-1, it activates IGF-1R tyrosine kinase signaling, engaging PI3K-Akt and MAPK/ERK pathways that drive protein synthesis, cell proliferation, and cell survival.
Typical results seen in research
In animal infusion studies (guinea pigs, pigs, rats), Long-R3 IGF-1 analogues produced greater and more sustained organ and tissue growth per unit dose than native IGF-1, an effect attributed to reduced sequestration by IGFBPs. Notably, a 2025 study in growth-restricted fetal sheep found that IGF-1 LR3 infusion did not promote additional fetal growth in that specific model, showing its growth-promoting effect is not universal. No controlled human trials of IGF-1 LR3 for muscle growth, fat loss, or recovery exist; a 2026 systematic review of performance-enhancing peptides classified it as evidence 'Tier D' — no peer-reviewed human studies, supported only by preclinical extrapolation and anecdotal user reports.
How it’s commonly used
In laboratory and research settings, IGF-1 LR3 is administered via injection, commonly subcutaneous, directly into or near the tissue under study, reflecting its use in animal and cell-culture protein-synthesis research rather than any approved clinical application. It is not taken orally, as a peptide of this size is degraded in the gastrointestinal tract.
- Journal of Molecular Endocrinology · 1992 Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency
- Journal of Endocrinology · 1996 Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection
- Journal of Endocrinology · 1995 Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig
- American Journal of Physiology-Endocrinology and Metabolism · 2025 IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep
- Frontiers in Endocrinology (Lausanne) · 2026 The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration
Curated from published literature for research orientation. Not an exhaustive review, and not a substitute for reading primary sources.