Which Peptides Are Best For Muscle Growth? IGF 1 LR3 Dosage: What to Know About Dosing, Safety, and Clinical Use IGF 1 LR3 does not promote growth in late gestation growth restricted fetal sheep American Journal of Physiology Endocrinology and Metabolism American Physiological Society IGF 1 LR3 (Insulin like Growth Factor 1 Long R3) is often called the "Holy Grail" of muscle building peptides because of its potent anabolic effects. In a Med Spa context, it is typically sought out Emerging Anabolic and Regenerative Peptides in Athletic Body Re composition and Bodybuilding: Mechanisms of Action, Dosing Strategies, and Evidence Review