Insulin-like Growth Factor 1 (IGF-1, Somatomedin C) is a 70-amino acid peptide hormone structurally similar to insulin. It is primarily produced by the liver in response to Growth Hormone (GH) stimulation and mediates many of GH's anabolic effects. IGF-1 is one of the most potent natural activators of the Akt/mTOR signaling pathway, driving cell growth, proliferation, and survival. In performance contexts, exogenous IGF-1 (specifically IGF-1 LR3, a modified long-acting variant) is used for its powerful anabolic and hyperplastic (new cell creation) properties. Unlike most anabolic compounds that only cause hypertrophy (enlargement of existing cells), IGF-1 can stimulate hyperplasia, creating entirely new muscle fibers.
Notes
Pharmaceutical IGF-1 (mecasermin, brand name Increlex) is FDA-approved for severe IGF-1 deficiency. IGF-1 LR3 is a research compound not approved for human use. This is an advanced compound with significant risks and should only be considered by experienced users who understand and can manage those risks.
IGF-1 binds to the IGF-1 receptor (IGF-1R), a tyrosine kinase receptor, activating the PI3K/Akt/mTOR signaling cascade. This is the most potent known activator of protein synthesis and cell proliferation in muscle tissue. Key effects: (1) Stimulates satellite cell activation and differentiation, creating new muscle cells (hyperplasia); (2) Promotes protein synthesis via mTOR activation; (3) Inhibits protein degradation; (4) Promotes glucose uptake independent of insulin; (5) Stimulates amino acid uptake into cells; (6) Promotes differentiation of stem cells into muscle cells. IGF-1 LR3 is a modified variant with a 13-amino acid extension at the N-terminus and an Arg-to-Glu substitution at position 3, reducing its binding to IGF binding proteins (IGFBPs) by 100-fold, resulting in much greater bioactivity and a longer half-life.
Endogenous IGF-1 circulates primarily bound to IGFBP-3 in a ternary complex with ALS (acid-labile subunit), extending its half-life to 12-15 hours. Free (unbound) IGF-1 has a half-life of only minutes. IGF-1 LR3 has dramatically reduced IGFBP binding, meaning more circulates in the free, active form, but with a half-life of 20-30 hours. This makes LR3 significantly more potent per mcg than native IGF-1. Metabolism is primarily hepatic and renal.
Typical Dose
IGF-1 LR3: 20-60 mcg per day. Beginners: 20-30 mcg/day. Intermediate: 40-50 mcg/day. Advanced: 50-80 mcg/day (higher doses carry significantly increased risk). Pharmaceutical mecasermin: dosed based on clinical indication, typically 40-120 mcg/kg twice daily. Cycles are typically kept short: 4-6 weeks.
Frequency
Once or twice daily. If using once daily, post-workout timing is popular. If splitting, AM and post-workout. Cycle lengths are typically 4-6 weeks with equal time off.
Administration
Subcutaneous or intramuscular injection. IGF-1 LR3 (the most common exogenous form) is injected subcutaneously. Some protocols use intramuscular injection into specific muscle groups for localized hyperplastic effects, though this approach is debated. Mecasermin (Increlex) is the pharmaceutical IGF-1 product.
Half-Life
IGF-1: 12-15 hours (bound to IGFBPs). IGF-1 LR3: 20-30 hours (extended half-life due to reduced IGFBP binding). Unbound IGF-1: approximately 10 minutes.
Contraindications
No PCT required for IGF-1 alone, as it does not suppress testosterone or the HPTA. However, IGF-1 may suppress endogenous GH production through negative feedback. Natural GH pulsatility typically recovers within 1-2 weeks of discontinuation. If stacking with anabolic compounds, PCT for those compounds is still necessary.