IGF-1 LR3, also known as LR3-IGF-1, is an elongated and modified version of naturally occurring IGF-1. The naturally occurring 70-amino acid form of activated IGF-1 is essential for normal human growth and development and acts via IGF-1 receptors to exert an anabolic effect to build muscle, which is why IGF-1 is important in bodybuilding . Low IGF-1 peptide levels are linked to poor growth and a number of metabolic disorders . Multiple tissues inside the body produce IGF-1 and its site of synthesis affects its function. The majority of IGF-1 is made by the liver and is transported to other tissues in the bloodstream, acting as an endocrine hormone . Importantly, IGF-1 is a central growth hormone that controls the anabolic growth promoting effect of growth hormone. It also has a growth hormone independent growth-stimulating effect, which is optimised when combined with human growth hormone (HGH) . In comparison to IGF-1, IGF-1 LR3 contains 13 extra amino acids and has the amino acid arginine substituted in position 3 . These additional amino acids increase the potency of IGF-1 LR3 to three times that of IGF-1 since it has around 1% affinity for IGF-binding proteins, which act to block the growth-promoting effects of IGF-1 [5, 6]. The modified IGF-1 LR3 peptide also has improved metabolic stability and remains active in the body for longer than IGF-1 . The reduced protein binding and longer half-life means that the peptide is free to promote muscle and bone growth and repair and smooth muscle survival [8, 9]. IGF-I LR3 has been shown to stimulate muscle growth and increase muscle mass by up to 50% . Additionally, IGF�s also modulate how the body utilises glucose via insulin signalling and can stimulate free fatty acid utilisation and fat loss . IGF-1 LR3 has an extended half-life of between 20 and 30 hours, which is around twice that of unmodified IGF-1 . The long half-life means that IGF-1 LR3 only needs to be dosed once per day, either subcutaneously or intramuscularly and will increase lean muscle growth and promote fat reduction and weight loss throughout the whole body. Up to 100 mcg can be dosed each day. A standard IGF-1 LR3 cycle should last four weeks and should be stacked with an anabolic androgenic steroid for optimal results. Side effects of IGF-1 LR3 may include headaches and nausea since the peptide can induce a hypoglycaemic state. High levels of this hormone have also been shown to promote organ enlargement, so never exceed the recommended dose of 100 mcg per day. References 1. Shavlakadze, T., et al., Reconciling data from transgenic mice that overexpress IGF-I specifically in skeletal muscle. Growth Horm IGF Res, 2005. 15(1): p. 4-18. 2. Cohen, J., et al., Managing the Child with Severe Primary Insulin-Like Growth Factor-1 Deficiency (IGFD): IGFD Diagnosis and Management. Drugs in R&D, 2014. 14(1): p. 25-29. 3. Mauras, N., Growth hormone, IGF-I and growth. New views of old concepts. Modern endocrinology and diabetes series, volume 4. Trends in Endocrinology & Metabolism, 1997. 8(6): p. 256-257. 4. Laron, Z., Insulin-like growth factor 1 (IGF-1): a growth hormone. Molecular Pathology, 2001. 54(5): p. 311-316. 5. Tomas, F.M., et al., Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection. J Endocrinol, 1996. 150(1): p. 77-84. 6. Mohan, S. and D.J. Baylink, IGF-binding proteins are multifunctional and act via IGF-dependent and -independent mechanisms. J Endocrinol, 2002. 175(1): p. 19-31. 7. von der Th�sen, J.H., et al., IGF-1 Has Plaque-Stabilizing Effects in Atherosclerosis by Altering Vascular Smooth Muscle Cell Phenotype. The American Journal of Pathology, 2011. 178(2): p. 924-934. 8. Sunters, A., et al., Mechano-transduction in osteoblastic cells involves strain-regulated estrogen receptor alpha-mediated control of insulin-like growth factor (IGF) I receptor sensitivity to Ambient IGF, leading to phosphatidylinositol 3-kinase/AKT-dependent Wnt/LRP5 receptor-independent activation of beta-catenin signaling. J Biol Chem, 2010. 285(12): p. 8743-58. 9. Patel, V.A., et al., Defect in insulin-like growth factor-1 survival mechanism in atherosclerotic plaque-derived vascular smooth muscle cells is mediated by reduced surface binding and signaling. Circ Res, 2001. 88(9): p. 895-902. 10. Tomas, F.M., et al., Insulin-like growth factor-I and more potent variants restore growth of diabetic rats without inducing all characteristic insulin effects. Biochemical Journal, 1993. 291(Pt 3): p. 781-786. Clemmons, D.R., Metabolic Actions of IGF-I in Normal Physiology and Diabetes. Endocrinology and Metabolism Clinics of North America, 2012. 41(2): p. 425-443.