RESEARCH MONOGRAPH · KDC-MN-087

IGF-1 LR3

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

57/100

Long-acting IGF-1 analog with real receptor activity but a sourcing landscape that's genuinely problematic

IGF-1 LR3 (Long Arg3 IGF-1) is a recombinant IGF-1 variant with an N-terminal 13-residue extension plus an Arg3 substitution, both of which reduce binding to IGF-binding proteins. The result is a circulating peptide that doesn't get sequestered by IGFBP-3 (which carries most endogenous IGF-1) and therefore has dramatically higher receptor availability at equivalent serum concentrations. Half-life extends to roughly 20-30 hours from native IGF-1's 10-12 minutes free, depending on how you measure.

What we like, from a research standpoint: as a tool compound for IGF-1 receptor pharmacology, LR3 is unusually clean because the IGFBP-displacement variable is controlled. For cell culture work, animal models of IGF-1 signaling, and studying receptor downstream pathways (PI3K/Akt, MAPK) without the confound of binding protein modulation, IGF-1 LR3 is genuinely useful. The Cera and Chemicon analytical work in the 90s established the receptor binding profile well.

What we dont like is everything about how the bodybuilding scene treats this molecule. Chronic supraphysiological IGF-1 receptor activation has serious theoretical implications for proliferative tissue states; the hypoglycemia risk from cross-reactivity with the insulin receptor at higher doses is real (the Arg3 substitution doesn't eliminate insulin receptor binding entirely); and the long half-life means that adverse effects, when they occur, persist longer than with native IGF-1.

Sourcing is the killer issue. IGF-1 LR3 is a 83-residue recombinant protein that requires bacterial expression and refolding, and the quality control on most commercial preparations is genuinely poor. The molecule is prone to disulfide misfolding, the recovery from inclusion bodies is variable, and "IGF-1 LR3" purchased from low-end suppliers is often a mix of correctly-folded peptide plus misfolded variants plus N-terminal truncation products. HPLC purity numbers without proper biological activity assays are misleading here.

For serious IGF-1 receptor pharmacology research, source from vendors with full analytical packages including bioactivity testing (typically MCF-7 or 3T3 proliferation assays). For everything else, the risk-evidence math is much worse than the supplement scene treats it.

Evidence: 55
Mechanism: 78
Reliability: 60
Safety: 40
Sourcing: 50
Value: 55
Signal: 65
Staying power: 50

Plain-language summary Intrigue 65 / 100

IGF-1 LR3 is a long-acting modified form of insulin-like growth factor 1. The R3 modification reduces binding to IGF-binding proteins, extending the half-life from minutes to hours. Used in research contexts for muscle growth studies. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Long Arg3 IGF-1 analog

A long-acting analog of IGF-1 with N-terminal extension and Arg3 substitution that reduces IGFBP binding and extends plasma half-life.

Abstract

IGF-1 LR3 (Long R3 IGF-1; CAS 946870-92-4; molecular weight 9111) is a recombinant analog of human IGF-1 with two structural modifications: a 13-residue N-terminal extension derived from the methionyl-N-terminal region of porcine GH, and substitution of arginine for glutamic acid at position 3. Both modifications reduce binding to IGF binding proteins (IGFBPs), which extends the plasma half-life and increases free bioavailable IGF-1 activity at IGF-1 receptors. The compound was originally developed for cell culture applications (mammalian cell growth media); research-grade availability supports investigational use. Pharmacokinetics: plasma half-life approximately 20 to 30 hours (versus 12 to 15 hours for native IGF-1). The compound is sold as a research chemical at concentrations typically 1 mg/mL. Investigational doses for performance applications range widely (20 to 100 micrograms, reported research dose ranges in the literature) but the safety profile of long-term IGF-1 elevation is poorly characterized; chronic IGF-1 elevation is implicated in increased cancer risk and acromegalic features.

Mechanism of action

IGF-1 receptor agonist with reduced IGFBP binding (Arg3 substitution + N-terminal extension). Extended half-life.

Reported research dose ranges

20 to 100 micrograms SC (reported research dose ranges in the literature); safety of chronic exposure poorly characterized.

References

Tomas FM, et al. Pharmacology of long-R3-IGF-1. J Endocrinol 1993.

Read the full monograph

The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, reported research dose ranges, sourcing and quality verification, reconstitution and handling, stack interaction considerations, and a curated reference list. Available as a research-use-only PDF download.

KDC-MN-087

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

Kodiac sells research compounds for investigative use only.

IGF-1 LR3

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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