Scientific Reference

IGF-1 LR3 (Long R3 IGF-1)

Evidence profile: Controlled human evidence

IGF-1 LR3 is a synthetic 83-amino acid analog of insulin-like growth factor-1 (IGF-1), modified with an arginine substitution at position 3 and an extended N-terminal sequence. These modifications significantly reduce binding to IGF-binding proteins (IGFBPs), resulting in prolonged circulation and increased bioavailability. Unlike native IGF-1, which has a short half-life, IGF-1 LR3 exhibits a substantially extended half-life (~20–30 hours), allowing sustained activation of IGF-1 receptors. Despite its potency and widespread research use, it has never been approved for human use and lacks clinical trial data, remaining strictly a research compound.