IGF1-LR3 (Long Arg3 IGF-1)
IGF-1 analog designed to evade binding proteins; human evidence for LR3: practically nonexistent.
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Quick summary
IGF1-LR3 is a synthetic analog of insulin-like growth factor 1 (IGF-1). Compared to native IGF-1, it has an arginine at the 3rd position and an N-terminal extension that reduces its binding to IGFBPs, leaving more of it “free” to activate the IGF-1R receptor. In forums, it is sold as a hypertrophy tool. In indexed literature, almost everything is animal or cellular. There are no published randomized clinical trials dosing IGF1-LR3 in healthy adult humans. It is useful to distinguish between: - A. Mecasermin (rhIGF-1): an approved drug for severe primary IGF-1 deficiency (children). - B. Research-grade IGF1-LR3: it is not that drug; its actual purity and dosage are not verified by a regulator.
Studied for
How it works
Activates the IGF-1R receptor (PI3K/Akt/mTOR and MAPK pathways). By binding less to IGFBPs, the analog can generate a more sustained mitogenic signal than native IGF-1 at equivalent doses in models. This also explains the theoretical concern for hypoglycemia and unwanted cell proliferation.
What the research says
Humans (LR3): there are no indexed RCTs for the compound. PubMed searches for “IGF-1 LR3” / “Long R3 IGF-1” primarily return animal models (sheep fetuses, mice, cells). Clinical context of native IGF-1: mecasermin has a label and post-marketing surveillance (hypoglycemia; warnings of neoplasms in unapproved uses or high doses). This does not validate LR3, but it does illustrate the risks of the IGF-1R pathway. Preclinical: there is interest in neurodegeneration and growth models; it does not demonstrate safe hypertrophy in healthy adults. Unknown: chronic safety, quantified oncological risk, supported human dosage.
Sources
Evidence level
D — Preclinical / no human RCTs of LR3
What's most reported
- In communities: muscle gain / recovery (anecdotal; often with other anabolics)
- In models: effects on growth/tissues depending on species and pathway
- Theoretical risk: hypoglycemia and sustained mitogenic signaling
Common side effects
No systematic human safety profile for LR3. By analogy with the IGF-1 axis: hypoglycemia, edema, arthralgias; concern for neoplasia with chronic IGF-1R activation. Internet products: unverified impurities and identity.
Combines / does not combine
Avoid combining with other potent growth signals without supervision (GH, other IGF analogs). Soft contraindication: history of cancer or suspected neoplasia. No clinically validated stacks exist.
Frequently asked questions
No. Increlex is native rhIGF-1 with a specific pediatric indication. Research-grade LR3 is not that medication.
There are no published RCTs supporting it as a hypertrophy or recovery therapy in adults.
IGF-1R drives proliferation and anti-apoptosis; LR3 maximizes the free fraction. Epidemiology associates high circulating IGF-1 with certain cancers; the quantified risk of LR3 in humans has not been measured.
Growth factors / IGF are on the anti-doping radar (WADA list of hormones and growth factors). Check the current list.
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Educational content. Not medical advice or usage guidelines. Research products are not approved medications unless otherwise indicated.