Insulin-like growth factor 1

Insulin-like growth factor 1 (IGF-1) is a 70-amino-acid peptide hormone with a structure similar to insulin. It is synthesized chiefly in the liver in response to growth hormone stimulation, but local production occurs in many tissues, including skeletal muscle. IGF-1 is the principal effector of GH’s anabolic actions on muscle, bone, and cartilage.

Mechanism

IGF-1 signals via the IGF-1 receptor, a transmembrane tyrosine kinase homologous to the insulin receptor. Activation triggers the PI3K–Akt–mTOR pathway, driving protein synthesis, and the MAPK pathway, driving cell proliferation. The hormone is largely bound in serum to IGF-binding proteins (IGFBPs), which extend its half-life and modulate bioavailability.

Therapeutic and non-medical use

Recombinant IGF-1 (mecasermin) is FDA-approved for severe primary IGF-1 deficiency. Non-medical use targets hypertrophy and recovery. Analogues such as IGF-1 LR3 carry an N-terminal extension that resists IGFBP binding and extends activity.

WADA classification

IGF-1 and its analogues appear on the WADA prohibited list under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), banned both in and out of competition.