IGF-1 LR3
Long R3 IGF-1 / LR3-IGF-1 / Insulin-like Growth Factor 1 Long R3
IGF-1 LR3 (Long Arg3 IGF-1) is a modified version of insulin-like growth factor 1 with an arginine substitution at position 3 and a 13-amino acid extension at the N-terminus, resulting in significantly reduced binding to IGF-binding proteins. This modification increases its bioavailability and half-life from minutes to approximately 20-30 hours, making it one of the most potent growth factors available for research. It promotes muscle hypertrophy, hyperplasia, and enhanced nutrient uptake in target tissues.
Mechanism of Action
Modified form of IGF-1 with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension. These modifications prevent IGF binding protein (IGFBP) sequestration, dramatically increasing bioavailability and potency compared to native IGF-1.
Research Protocols
For research purposes only. Not medical advice.
Research protocols use 20-60mcg daily via subcutaneous or intramuscular injection. Often administered post-workout. Cycles limited to 4-6 weeks due to potency. Splitting dose bilaterally may improve localized effects.
Research Notes
Clinical Research Status
IGF-1 LR3 is a research-grade compound that has not undergone formal clinical development for any therapeutic indication. Native IGF-1 (mecasermin/Increlex) is FDA-approved for severe IGF-1 deficiency, but the LR3 variant has no regulatory pathway. It is used extensively in cell culture and in vitro research due to its potent proliferative effects and reduced binding protein interference. No Phase 1 human trials of IGF-1 LR3 specifically have been conducted.
Key Published Findings
In vitro and animal studies demonstrate IGF-1 LR3 has approximately 2-3 times the potency of native IGF-1 due to its reduced sequestration by IGF-binding proteins (particularly IGFBP-3). Research shows it activates the PI3K/Akt and MAPK pathways promoting both muscle protein synthesis and satellite cell proliferation (hyperplasia). Unlike GH which acts systemically, IGF-1 LR3 has direct anabolic effects on muscle tissue without requiring hepatic conversion.
Safety Profile
IGF-1 LR3 carries a higher risk profile than most peptides due to its potent, long-acting proliferative effects on all tissues including potentially cancerous cells. Hypoglycemia is a significant acute risk due to insulin-like metabolic activity, particularly at higher doses or with concurrent insulin use. Long-term concerns include potential acceleration of undetected neoplasms, organ growth (intestinal hypertrophy), and insulin receptor desensitization. No human safety data exists for this specific variant.
Comparison to Related Compounds
Compared to native IGF-1 (mecasermin), IGF-1 LR3 has dramatically extended half-life and higher free-fraction concentration due to poor IGFBP binding. Relative to GH or GH-releasing peptides, IGF-1 LR3 bypasses the entire GH/IGF axis and acts directly, producing more predictable but less physiological tissue growth. Unlike MGF (a splice variant focused on muscle repair), IGF-1 LR3 has broader systemic anabolic effects on multiple tissue types.
Community Observations
IGF-1 LR3 is considered among the highest-risk peptides in research circles due to its non-selective proliferative effects and lack of human safety data. Users report pronounced muscle fullness and accelerated recovery, but also significant hypoglycemia risk requiring careful carbohydrate management. The research community emphasizes that its growth-promoting effects are not tissue-specific, raising concerns about intestinal polyp growth, cardiac hypertrophy, and tumor promotion.
Half-Life
~20-30 hours
Reconstitution
Bacteriostatic water (BAC) or 0.6% acetic acid
Storage
Lyophilized
Refrigerate 2-8C up to 24 months.
Reconstituted
Refrigerate 2-8C. Use within 14 days.
US Legal Status
Also Known As
PeptideVault provides research-based summaries for informational purposes only. We do not host, distribute, or endorse vendor documentation. All certificates of analysis, GMP certificates, and vendor communications must be requested and verified directly by the buyer. Nothing on this platform constitutes legal, medical, or professional advice. Users are solely responsible for verifying vendor credentials and ensuring compliance with all applicable local, state, and federal laws before purchasing any research chemicals. Use of this platform constitutes acceptance of full personal responsibility.
Read full disclaimer