IGF-1 LR3 (Long Arginine 3-Insulin-like Growth Factor 1) is a synthetic protein, a modified version of natural IGF-1, engineered for increased potency and a longer lifespan in the body, making it more effective for cell growth and muscle building in research and potentially for therapeutic use, though it has a strong association with banned substances in sports and research use. Its key modifications include an arginine substitution and an N-terminal peptide extension, which prevent it from binding strongly to IGF-binding proteins, giving it a longer half-life (around 20-30 hours) than natural IGF-1, and it directly promotes muscle growth and tissue repair by boosting protein synthesis.