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Research-onlyVendors pendingFacts verified · 2026-05-25

IGF-1 LR3

Also known as long r3 igf-1, lr3 igf-1 · Wikipedia

IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid analog of native human IGF-1 engineered with an arginine-for-glutamate substitution at position 3 plus a 13-residue N-terminal extension. These modifications reduce affinity for the IGF binding proteins (principally IGFBP-3) by roughly two orders of magnitude while preserving full affinity for the IGF-1 receptor, producing a markedly higher free, bioactive fraction and a substantially longer functional half-life than native IGF-1. It is FDA-cleared as a research-use-only cell-culture reagent (the industry-standard IGF-1 analog for serum-free media) and is on the WADA Prohibited List. Human in vivo use is entirely off-label / research only. Also known as: Long R3 IGF-1; LR3 IGF-1.

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Mechanism of action

IGF-1 LR3 is an 83-amino-acid recombinant analog of human IGF-1 carrying two modifications: substitution of arginine for glutamate at position 3 and a 13-residue N-terminal MFPAMPLSSLFVN extension [Francis 1996, PMID 8708565]. These changes lower binding affinity for IGFBPs (especially IGFBP-3) by ~100-fold while retaining native affinity for the IGF-1 receptor (IGF-1R) [Tomas 1995, PMID 7561636].

IGF-1 LR3 is an 83-amino-acid recombinant analog of human IGF-1 carrying two modifications: substitution of arginine for glutamate at position 3 and a 13-residue N-terminal MFPAMPLSSLFVN extension [Francis 1996, PMID 8708565]. These changes lower binding affinity for IGFBPs (especially IGFBP-3) by ~100-fold while retaining native affinity for the IGF-1 receptor (IGF-1R) [Tomas 1995, PMID 7561636]. The result is a higher free, bioactive circulating fraction [Owens 1991]. Receptor activation triggers PI3K/Akt/mTOR (protein synthesis, anti-apoptosis, cell growth) and Ras/MAPK/ERK (proliferation) cascades systemically [Bayes-Genis 2000]. Because LR3 IGF-1 bypasses the IGFBP buffering system, in vivo exposure is non-physiologic and the effective potency is roughly three-fold higher than equimolar native IGF-1.

Pharmacokinetic properties

Half-life

~20-30 hours (free, bioactive form; vs ~10-15 min for native IGF-1)

Routes

subcutaneous · intramuscular

Bioavailability

Systemic action with daily SC dosing. ~3x more potent than native IGF-1 due to reduced IGFBP sequestration.

Amino-acid sequence

(83 aa) MFPAMPLSSL FVNGPRTLCG AELVDALQFV CGDRGFYFNK PTGYGSSSRR APQTGIVDEC CFRSCDLRRL EMYCAPLKPA KSA

Use & research dosing

StrengthEndurance

Not FDA-approved for any human indication (research framing only). LR3 IGF-1 is manufactured commercially as a cell-culture reagent at 50-100 ng/mL working concentrations in serum-free media, where it is well characterized. In self-experimentation and underground performance-enhancement protocols reported in the research-chemical literature, doses are typically 20-50 mcg/day subcutaneously, administered pre- or post-training in 4-6 week cycles, with deload weeks between cycles. WADA prohibits IGF-1 and its analogs in and out of competition for all athletes; detection methods by LC-MS in plasma have been published.

Research-use framing only. SavePeptides sells nothing for human consumption. Doses above reflect reported research / self-experimentation ranges, not clinical recommendations.

Editorial perspective

Originally designed by Francis and colleagues for cell-culture applications, LR3 IGF-1 is now the de facto reference IGF-1 analog in serum-free media and stem-cell research. Human use is entirely off-label / underground. The 20-30 hour functional half-life produces continuous, non-pulsatile IGF-1R activation that is biologically distinct from native pulsatile IGF-1 signaling, raising both efficacy and carcinogenesis questions that have not been resolved in human trials. Detection methods by LC-MS in plasma have been published, enabling anti-doping enforcement [Thomas 2017, PMID 28668757].

— SavePeptides editorial desk · last updated 2026-05-25

Cautions & contraindications

Before researching this compound, note:

  • not FDA-approved for any human use; WADA Prohibited List (S2 peptide hormones, growth factors)
  • significant hypoglycemia risk due to insulin-like activity at the insulin receptor
  • contraindicated in active or suspected malignancy (potent PI3K/Akt mitogen)
  • avoid in pregnancy and breastfeeding
  • avoid in active proliferative diabetic retinopathy (IGF-1 axis activation can accelerate progression)
  • chronic high-dose exposure may produce organomegaly (cardiac, renal, intestinal)
  • may cause acromegaly-like changes (jaw, hands, feet) with prolonged use
  • lipodystrophy and lipoatrophy at the injection site reported
  • lethargy, headache, and jaw pain commonly reported at higher doses
  • non-pulsatile (continuous) IGF-1R activation differs biologically from native pulsatile signaling

Research foundation

The papers behind the page.

  1. [01]https://pubmed.ncbi.nlm.nih.gov/8708565/
  2. [02]https://pubmed.ncbi.nlm.nih.gov/7561636/
  3. [03]https://pubmed.ncbi.nlm.nih.gov/9488001/
  4. [04]https://pubmed.ncbi.nlm.nih.gov/28668757/

Facts verified

2026-05-25

Confidence

medium

What this means

  • WADA-banned (S2 growth factors) — anti-doping exposure
  • no human clinical trial program; all in vivo evidence is preclinical or underground self-experimentation

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