Growth Hormone · Body Composition · Endocrine
IGF-1 LR3
Also known as: Long R3 IGF-1, Long-Arg3-IGF-1, LR3-IGF-1
A modified, longer-acting analog of insulin-like growth factor 1 originally developed as a cell-culture reagent and used off-label for muscle and recovery effects.
Sign in to add to watchlistEvidence strength
Strength of human clinical evidence — A (strongest) to D (mostly preclinical). This reflects research maturity, not safety or suitability.
Vial Theory provides educational research summaries only. Content is not medical advice, diagnosis, treatment, dosing guidance, or individualized suitability screening. Regulatory status can change over time and varies by jurisdiction.
Key Takeaways
- ›IGF-1 LR3 is a long-acting, binding-protein-resistant IGF-1 analog originally made as a lab reagent.
- ›There are essentially no controlled human trials of this specific molecule.
- ›Because IGF-1 drives cell growth, long-term safety (including cancer-related concerns) is a serious unknown.
- ›It is not approved for human use and is on the WADA prohibited list; research-grade product isn't medical grade.
- ›Speak with a licensed healthcare professional before making any health-related decisions.
What It Is
IGF-1 LR3 is a modified analog of insulin-like growth factor 1 (IGF-1) carrying two structural changes: an N-terminal 13-amino-acid extension and a substitution at position 3 (arginine for glutamic acid) that reduces binding to IGF binding proteins (IGFBPs). These modifications substantially extend the analog's bioactive half-life relative to native IGF-1, which is rapidly sequestered by IGFBPs after administration.
The compound was developed primarily as a cell-culture reagent for biopharmaceutical manufacturing, where IGFBP-resistant IGF-1 is useful for supporting cell growth in serum-free media. It is widely manufactured at research-reagent grade and has been adopted off-label in athletic and bodybuilding contexts as an alternative to recombinant human IGF-1 (mecasermin).
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Disclaimer: This content is for educational and research purposes only and is not medical advice. Always consult a licensed healthcare professional before making health-related decisions.