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Muscle Growth5 cited studies

IGF-1 LR3

Long-acting IGF-1 analog with reduced IGFBP affinity — extended anabolic signalling.

Also known as: IGF-1 LR-3 · IGF1 LR3 · Long R3 IGF-1
SummaryMechanismDosingSafetyStudies
Research use only — not for human consumption.

What it is

IGF-1 LR3 (Long [Arg3] Insulin-like Growth Factor-1) is a peptide engineered to mimic IGF-1 with an extended N-terminal extension and an Arg3 substitution that reduces binding to IGF-binding proteins (IGFBPs), giving it a much longer functional half-life. Used in research for muscle growth, tissue repair, fat metabolism, and recovery, with downstream effects on bone, skin, and overall cellular regeneration.

Mechanism of action

IGF-1 LR3 binds IGF-1 receptors on muscle and other tissues, activating PI3K/Akt and MAPK pathways for protein synthesis, cell proliferation, and survival. Reduced IGFBP affinity increases free, bioavailable IGF-1 activity per dose versus native IGF-1.

Half-life: Functional half-life ~20–30 hours (versus minutes for native IGF-1).

Evidence summary

Animal studies (pigs, beef heifers, rodent food-restriction models) demonstrate body-composition and substrate-handling effects. Direct human RCT data is limited; off-label research use is common in athletic and recovery contexts.

Typical dosing protocols

Typical dose
20–80 mcg
Frequency
Once daily
Cycle length
4 weeks
  • 20–80 mcg subcutaneous, once daily
  • Short cycles (4 weeks) to avoid receptor downregulation and hypoglycemia
  • Best used during structured caloric/training program

Side effects & safety

  • Hypoglycemia possible — dose post-meal
  • Edema, joint discomfort, or carpal-tunnel-like symptoms at higher doses
  • Theoretical concern about chronic IGF-1 elevation and tissue overgrowth
Contraindications
  • • Active malignancy or uncontrolled diabetic retinopathy
  • • Pregnancy

Cited studies

  1. (1996). Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection. Journal of Endocrinology.
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  2. (1997). Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs. Journal of Endocrinology.
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  3. (1999). Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers. Domestic Animal Endocrinology.
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  4. (2001). Insulin-like growth factor-I (IGF-I) analogue, LR3IGF-I, ameliorates the loss of body weight but not of skeletal muscle during food restriction. Growth Hormone & IGF Research.
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  5. (2002). Effects of insulin-like growth factor-I and its analogue, long-R3-IGF-I, on intestinal absorption of 3-O-methyl-D-glucose are less pronounced than gut mucosal growth responses. Growth Factors.
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Disclaimer

All content is for research and educational purposes. Peptides described are sold for laboratory research use only and are not intended to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional before beginning any protocol.