IGF-1 LR3

Research-Grade

IGF-1 LR3 (Long R3 IGF-1) is a modified form of recombinant human IGF-1 with two substitutions: an arginine substituted at position 3, and a 13-amino-acid N-terminal extension from human growth hormone. The combined effect dramatically reduces binding to IGF-binding proteins (IGFBPs), leaving the peptide circulating in free, bioactive form for several hours rather than minutes. IGF-1 LR3 is used in research as a more potent and long-acting IGF-1 analog. Off-label athletic use pursues the anabolic effects of supraphysiologic IGF-1 elevation: muscle protein synthesis, myoblast proliferation, and enhanced recovery. Clinical use of native IGF-1 (mecasermin, Increlex) is restricted to severe primary IGF-1 deficiency in pediatric growth disorders. Safety concerns are significant. Hypoglycemia is common, because IGF-1 cross-reacts with the insulin receptor. Theoretical cancer-promotion risk with chronic supraphysiologic exposure is real: elevated IGF-1 is a recognized risk factor for several cancer types. Human safety data for off-label chronic IGF-1 LR3 dosing is essentially absent.