IGF-1 LR3 is a recombinant analog of insulin-like growth factor 1 with an extra arginine at position 3 and the first three N-terminal residues replaced. Extends half-life from ~10 minutes to ~20+ hours.
Mechanism — Binds IGF-1 receptor with similar affinity to native IGF-1 but with reduced affinity for binding proteins (IGFBPs). The result: more free, active IGF-1 over a longer window. Drives muscle protein synthesis, satellite cell activation, and tissue growth.
Use case — Hypertrophy phases in research settings. Typical dosing 20-50 mcg subcutaneous, often pre- or post-workout, in 4-6 week cycles.
Caveats — Real hypoglycemia risk — keep fast carbs on hand. IGF-1 receptor stimulation has theoretical cancer-promotion concerns; not for use in oncology-positive backgrounds. The long half-life is a feature for muscle but a risk for adverse events.