Last updated: May 18, 2026
What IGF-1 LR3 is
IGF-1 LR3 is a synthetic analog of human insulin-like growth factor 1 (IGF-1). The “LR3” designation refers to two structural modifications:
- L (Long): 13-amino-acid N-terminal extension (Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn)
- R3: Substitution of arginine for glutamic acid at position 3
These changes serve two purposes: the N-terminal extension and R3 modification reduce binding affinity for the six IGF binding proteins (IGFBPs), and the extended structure resists enzymatic degradation. Half-life extends from ~10 minutes (native IGF-1) to ~30 hours (LR3).
Mechanism
IGF-1 LR3 binds the IGF-1 receptor (IGF-1R) with similar affinity to native IGF-1. Receptor activation triggers:
- PI3K/Akt pathway activation — protein synthesis, cell survival
- Ras/Raf/MAPK pathway — cell proliferation
- mTOR activation — protein synthesis, glycogen storage
- Glucose uptake (mild insulin-like effect)
Because LR3 binds IGFBPs less than native IGF-1, more free LR3 reaches cell-surface receptors, producing a stronger and longer effect.
Research dosing protocols
Reported research-community dosing typically ranges 20-100 mcg per day, administered subcutaneously. The longer half-life means once-daily dosing is sufficient (vs multiple daily doses required for native IGF-1).
Common cycle: 4-6 weeks on, 4-6 weeks off. Continuous long-term use is not well-characterized in research literature.
Localized vs systemic effects
Some research-community protocols inject IGF-1 LR3 near specific muscles to encourage localized growth. The biology supports modest localization — IGF-1 receptors are abundant in muscle tissue and proximate injection produces higher local tissue concentrations before systemic distribution.
Safety considerations
IGF-1 elevation carries theoretical concerns about:
- Promoting growth of latent malignancies — IGF-1R is expressed on many cancer cells
- Insulin sensitivity changes — IGF-1 has insulin-like effects; chronic use may affect glucose homeostasis
- Cardiovascular effects — both protective and pro-hypertrophic effects observed depending on context
- Acromegaly-like effects with sustained supratherapeutic dosing
Common monitored labs during use: IGF-1 (target staying within reference range for age), fasting insulin, HbA1c.
Regulatory status
- US: Mecasermin (recombinant native IGF-1, Increlex) is FDA-approved for severe primary IGF-1 deficiency in children. IGF-1 LR3 is sold as a research peptide; not FDA-approved.
- WADA: Banned (S2 peptide hormones and growth factors)
- Australia (TGA): Restricted
What’s the difference between IGF-1 LR3 and IGF-1 DES?<br />
IGF-1 DES (1-3) is a 67-amino-acid truncated form of IGF-1 with the first three amino acids removed. Very short half-life (~5 min) and localized action. IGF-1 LR3 is the opposite — extended structure with long half-life for systemic effect.
Can IGF-1 LR3 be stacked with growth hormone peptides?<br />
Common research-community pairing — CJC-1295/Ipamorelin (stimulates GH → endogenous IGF-1) combined with exogenous IGF-1 LR3. The combination produces sustained IGF-1 elevation.
How long until effects show?<br />
Acute effects (glucose uptake, anabolic signaling) within hours. Measurable body composition changes typically take 4-6 weeks of consistent dosing.
Does IGF-1 LR3 cause hypoglycemia?<br />
Possible at higher doses due to insulin-like effects. Most protocols dose post-meal to minimize hypoglycemia risk.