IGF-1 (Insulin-like Growth Factor 1)

IGF-1 is a hormone produced mainly in the liver in response to growth hormone signals. It mediates most of what GH actually does in the body — muscle protein synthesis, bone growth, and fat metabolism are largely IGF-1-driven rather than directly GH-driven. When a GH secretagogue (sermorelin, CJC-1295, ipamorelin) raises GH levels, that GH travels to the liver and prompts more IGF-1 production. IGF-1 is what you measure to track whether a GH-stimulating protocol is doing anything. There's a complication. IGF-1 is a cell-growth signal — and cell growth is not universally a good thing. Chronically elevated IGF-1 is associated with increased cancer risk in the epidemiological literature. The direction of causation isn't clean, but it's why clinical protocols for GH-related compounds typically monitor IGF-1 and avoid pushing it significantly above the age-appropriate reference range. The evidence base for using GH secretagogues specifically to optimise IGF-1 in non-GH-deficient adults is thin. The mechanism is real. The human outcome data in healthy people is not.