IGF-1

The molecule is a 70-amino acid protein that your body already makes naturally, peaking during puberty and declining gradually with age. It works by binding to the IGF-1 receptor — a protein found on the surface of almost every cell in the body — and activating two major signalling cascades: one that drives protein synthesis and cell growth (PI3K/Akt), and one that drives cell proliferation and differentiation (MAPK/ERK). At high concentrations it can also bind to insulin receptors, which is why hypoglycaemia is the most serious clinical risk with exogenous use.

Increlex, the FDA-approved recombinant version, is prescribed exclusively for a rare paediatric condition called severe primary IGF-1 deficiency — children whose bodies cannot produce adequate IGF-1 despite normal or elevated growth hormone. It is not approved for adults, for anti-aging, for body composition, or for athletic performance. Outside that narrow indication, any use of recombinant IGF-1 is off-label and carries meaningful safety considerations, particularly a well-documented association between elevated IGF-1 and increased cancer risk.

The epidemiology here is nuanced but important: both very low and very high IGF-1 levels are associated with worse health outcomes. Normalising deficient IGF-1 appears beneficial; pushing levels above the physiological range does not reliably produce added benefit and carries real risk. The relationship between IGF-1 and cancer is permissive rather than causative — IGF-1 does not initiate tumours, but elevated levels accelerate the growth of existing or dormant ones by suppressing apoptosis and driving cell proliferation. That distinction matters, but it does not eliminate the concern.