IGF-1
The liver-derived 70-amino-acid polypeptide that serves as the principal mediator of growth hormone's anabolic effects on muscle, bone, and tissue.
IGF-1 is an endogenous 70-amino-acid polypeptide produced primarily in the liver in response to growth hormone signaling, functioning as the principal downstream mediator of GH's anabolic actions through the IGF-1 receptor (IGF-1R) expressed in virtually all tissues. It drives muscle protein synthesis, satellite cell activation, bone growth, and glucose uptake via PI3K/Akt and MAPK/ERK signaling. The recombinant form, mecasermin (Increlex), is FDA-approved for primary IGF-1 deficiency in children with growth hormone insensitivity syndrome, while research-grade IGF-1 is used off-label for performance and anti-aging purposes with meaningful safety caveats.
Class
Endogenous 70-amino-acid anabolic polypeptide (GH/IGF axis)
Half-life
~15 minutes (native IGF-1)
Routes
Subcutaneous, Intramuscular
Category
Growth Hormone & Performance
Researched benefits
What it's studied for
Muscle growth and protein synthesis
IGF-1 activates IGF-1R to drive PI3K/Akt signaling, promoting muscle protein synthesis and satellite cell activation. It is the principal downstream mediator through which growth hormone exerts its anabolic effects on skeletal muscle.
Recovery and tissue repair
By stimulating cell survival, proliferation, and satellite cell recruitment, IGF-1 supports repair of muscle and connective tissue. Its regenerative signaling underlies much of the recovery benefit attributed to GH-elevating interventions.
Bone growth
IGF-1 mediates GH-driven skeletal growth; in children with severe IGF-I deficiency, recombinant IGF-I therapy increased height velocity from 2.8 cm/year to 8.0 cm/year, establishing it as a primary growth mediator.
Fat metabolism
IGF-1 influences metabolic handling of nutrients and is studied for effects on fat metabolism alongside its role in glucose uptake in muscle and bone tissue.
Glucose uptake
Through IGF-1R and its overlap with insulin signaling, IGF-1 promotes glucose uptake in muscle. This insulin-like activity is central to both its anabolic profile and its glucose-homeostasis safety considerations.
Mechanism
How it works
IGF-1 binds the IGF-1 receptor (IGF-1R) with high affinity, a tyrosine kinase receptor expressed in virtually all tissues. Receptor activation triggers two principal downstream cascades: the PI3K/Akt pathway, which drives protein synthesis, cell survival, and glucose uptake, and the MAPK/ERK pathway, which promotes cellular proliferation. Together these signals produce IGF-1's characteristic anabolic and growth-promoting effects in muscle and bone.
As the principal mediator of growth hormone's anabolic actions, IGF-1 is produced primarily in the liver in response to GH signaling. Many GH-stimulating interventions exert their effects indirectly by elevating circulating IGF-1. Endogenous levels peak during puberty and decline with age, paralleling age-related changes in tissue regeneration and body composition.
The native peptide has a short circulating half-life of roughly 15 minutes because it is bound and regulated by IGF binding proteins (notably IGFBP-3), which sharply limits its free active window. This contrasts with engineered analogs such as IGF-1 LR3, whose reduced binding-protein affinity extends the half-life to roughly 20-30 hours. Co-administration of rhIGF-I with rhIGFBP-3 as a complex has been shown to sustain elevated circulating IGF-I for up to 24 hours in clinical study.
Because IGF-1R signaling promotes both cell proliferation and survival, IGF-1 excess carries mechanistic risks distinct from its benefits, including effects on glucose homeostasis (via its insulin-like activity), potential oncogenic cell signaling, and acromegaly-related cardiac and metabolic comorbidities seen with chronically elevated GH/IGF-1.
Evidence
Research & clinical studies (8)
Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity
In 76 children studied over 12 years, recombinant IGF-I therapy raised height velocity from a baseline of 2.8 cm/year to 8.0 cm/year in the first year, with anabolic effects sustained above baseline for up to 8 years.
PMID 17192294Pharmacokinetic studies of recombinant human insulin-like growth factor I (rhIGF-I)/rhIGF-binding protein-3 complex administered to patients with growth hormone insensitivity syndrome
A single subcutaneous injection of the rhIGF-I/rhIGFBP-3 complex raised circulating IGF-I into the normal range for a sustained 24-hour period in adolescents, improving the pharmacokinetic profile over rhIGF-I alone.
PMID 16403822Speckle-tracking echocardiography reveals the synergistic impact of GH/IGF-1 excess and metabolic dysregulation on cardiac dysfunction in acromegaly
Elevated IGF-1 directly drove subclinical cardiac dysfunction in acromegaly patients, amplified by metabolic dysregulation, with cardiac structure improving in those achieving biochemical remission.
PMID 42213228The biomarkers uCTX-II, CS846 and IGF-1 are associated with clinical and ultrasound scores in haemophilic arthropathy: a cross-sectional study
IGF-1 negatively correlated with joint damage severity in severe hemophilia, identifying it as a candidate biomarker for hemophilic arthropathy severity.
PMID 42217051Early-onset colorectal cancer in Australia: environmental, microbial, and policy implications
Reviewed evidence implicating IGF-1-mediated signaling, alongside insulin resistance and chronic inflammation, as a mechanism linking cumulative environmental exposures to rising early-onset colorectal cancer.
PMID 42213629Stimulating Thyrotropin Receptor Antibodies Enhance the Expression of Both Thyrotropin Receptors and Insulin-Like Growth Factor 1 Receptors in Fibroblasts
Stimulating TSH-receptor antibodies upregulated both TSH receptors and IGF-1 receptors in fibroblasts, illustrating IGF-1R crosstalk in autoimmune thyroid-associated pathology.
PMID 42374926Efficient in vivo removal of solubility tag to improve the bacterial production of soluble, bioactive human IGF-1
Co-expressing TEV protease with a solubility-tagged human IGF-1 fusion enabled in vivo tag removal, yielding tag-free IGF-1 with bioactivity comparable to commercial forms.
PMID 42371234IGF-2-mediated hypoglycemia in a patient with a phyllodes tumor of the breast: a rare presentation of non-islet cell tumor hypoglycemia
A phyllodes tumor caused non-islet cell tumor hypoglycemia via IGF-2 secretion, with an elevated IGF-2:IGF-1 ratio proving a more reliable diagnostic indicator than absolute IGF-2 levels.
PMID 42214434Safety
Side effects & considerations
Commonly reported effects
Contraindications & cautions
- Active cancer or cancer history (IGF-1R signaling can promote proliferation and survival)
- Diabetes
- Pregnancy or nursing
IGF-1 carries a moderate risk profile. Because IGF-1R signaling promotes cell proliferation and survival, chronic elevation raises concerns about oncogenic signaling, glucose dysregulation, and acromegaly-related cardiac and metabolic comorbidities. Review contraindications and consult a qualified professional before any use.
FAQ
IGF-1 — common questions
What is IGF-1?
IGF-1 (insulin-like growth factor 1; somatomedin C) is an endogenous 70-amino-acid polypeptide produced primarily in the liver in response to growth hormone signaling. It is the principal mediator of GH's anabolic effects, acting through the IGF-1 receptor expressed in virtually all tissues to drive muscle protein synthesis, bone growth, and cellular proliferation via PI3K/Akt and MAPK/ERK signaling.
What is IGF-1 primarily studied for?
Its main research areas are muscle growth, recovery, fat metabolism, tissue repair, and its central role in the GH/IGF axis.
How is IGF-1 different from IGF-1 LR3?
Native IGF-1 has a very short half-life of roughly 15 minutes because IGF binding proteins rapidly sequester it. The engineered LR3 analog has reduced binding-protein affinity, extending its half-life to roughly 20-30 hours, which is why analogs are often preferred in research contexts.
Is IGF-1 FDA-approved?
The recombinant form, mecasermin (Increlex), is FDA-approved (effective August 30, 2005) specifically for primary IGF-1 deficiency in children with growth hormone insensitivity syndrome. This narrow pediatric indication is distinct from performance-enhancing or anti-aging uses, which are not approved.
What are the side effects of IGF-1?
Reported contraindications and considerations include active cancer or cancer history, diabetes, and pregnancy or nursing. Because IGF-1R signaling promotes cell proliferation and survival, key safety concerns are glucose dysregulation, potential oncogenic signaling, and acromegaly-related comorbidities.
How is IGF-1 administered?
Reported routes of administration are subcutaneous and intramuscular injection.
What does the research show about IGF-1?
A 12-year study of 76 children with severe IGF-I deficiency found that recombinant IGF-I therapy increased height velocity from a baseline of 2.8 cm/year to 8.0 cm/year in the first treatment year, with anabolic effects maintained above baseline for up to 8 years, establishing IGF-I as a primary growth and anabolic mediator.
