Insulin-like Growth Factor 1 (IGF-1) is a 70-amino acid protein structurally similar to insulin. It is primarily produced by the liver in response to growth hormone stimulation and mediates many of GH's growth-promoting effects. Recombinant human IGF-1 (mecasermin, brand name Increlex) is FDA-approved for the treatment of severe primary IGF-1 deficiency (primary IGFD) — a condition where patients have normal or elevated GH but fail to produce adequate IGF-1. IGF-1 plays critical roles in growth, development, and metabolism throughout life. It circulates bound to IGF binding proteins (primarily IGFBP-3 in a ternary complex with acid-labile subunit).
Category: Growth Factor. Evidence rating: A (strong human clinical data).
Clinical status: FDA-approved (Increlex/mecasermin) for severe primary IGF-1 deficiency.
IGF-1 binds to the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase that activates the PI3K/Akt pathway (promoting cell survival and protein synthesis) and the MAPK/ERK pathway (promoting cell proliferation). In circulation, 95-99% of IGF-1 is bound to IGF binding proteins, primarily IGFBP-3 in…
Safety considerations: Hypoglycemia is the most common and serious adverse effect (FDA black box warning on Increlex) — occurs in up to 50% of patients; Must be administered with a meal to reduce hypoglycemia risk; Injection site reactions common.
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-07-05.
Related peptides: IGF-1 LR3, Follistatin 344, MGF.
Compare: IGF-1 vs IGF-1 LR3, IGF-1 vs Follistatin 344, IGF-1 vs MGF.
Primary IGF-1 deficiency means the body produces normal or elevated growth hormone but cannot produce adequate IGF-1, usually due to GH receptor defects (Laron syndrome), IGF-1 gene deletions, or post-receptor signaling defects. These patients do not respond to GH treatment and require direct IGF-1 replacement.
GH is a 191-amino acid pituitary hormone that signals the liver to produce IGF-1. IGF-1 (70 amino acids) then mediates many of GH's growth and anabolic effects. They are sequential components of the same growth axis. GH has additional direct metabolic effects (lipolysis, diabetogenic) that IGF-1 does not share — in fact, IGF-1 has insulin-like glucose-lowering effects.
Epidemiological studies consistently associate higher circulating IGF-1 levels with modestly increased risk of certain cancers (prostate, breast, colorectal). However, association does not prove causation, and IGF-1 levels within the normal range are not considered a cancer risk factor by clinical guidelines. Mecasermin is contraindicated with active malignancy.