What Are the Best Peptides for Muscle Growth? IGF 1 LR3 Peptide Clinics IGF 1 LR3 100mcg 1mg Peptide Bulk Supply 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 IGF 1 LR3: Dosage Results and Safety Guide Vita Bella Health Thaiger IGF 1 LR3 Powerful Muscle Growth Peptide