--- title: "IGF-1 LR3 | PepTracker Pro" description: "A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development." lang: en json-ld: | [ { "@context": "https://schema.org", "@type": "Organization", "name": "PepTracker Pro", "url": "https://peptrackerpro.com", "logo": "https://peptrackerpro.com/favicon.png", "description": "Evidence-based educational resource dedicated to improving peptide research literacy.", "contactPoint": { "@type": "ContactPoint", "email": "hello@peptrackerpro.com", "contactType": "customer support" }, "sameAs": [] }, { "@context": "https://schema.org", "@type": "MedicalWebPage", "name": "IGF-1 LR3", "description": "A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development.", "url": "https://peptrackerpro.com/peptides/igf-1-lr3", "lastReviewed": "2026-05-27", "reviewedBy": { "@type": "Organization", "name": "PepTracker Pro Research Team", "url": "https://peptrackerpro.com" }, "isPartOf": { "@type": "WebSite", "name": "PepTracker Pro", "url": "https://peptrackerpro.com" } }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://peptrackerpro.com" }, { "@type": "ListItem", "position": 2, "name": "Peptides", "item": "https://peptrackerpro.com/peptides" }, { "@type": "ListItem", "position": 3, "name": "IGF-1 LR3", "item": "https://peptrackerpro.com/peptides/igf-1-lr3" } ] }, { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "People researching IGF-1 pathway compounds?", "acceptedAnswer": { "@type": "Answer", "text": "IGF-1 LR3 is a research peptide studied in preclinical models. A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development." } }, { "@type": "Question", "name": "Those comparing direct vs indirect GH approaches?", "acceptedAnswer": { "@type": "Answer", "text": "IGF-1 LR3 is a research peptide studied in preclinical models. A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development." } }, { "@type": "Question", "name": "Individuals studying tissue growth factors?", "acceptedAnswer": { "@type": "Answer", "text": "IGF-1 LR3 is a research peptide studied in preclinical models. A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development." } } ] } ] --- [Skip to main content](#main) **Educational information only.** This site does not provide medical advice. [Read full disclaimer](/disclaimer) [PepTracker Pro](/) [Home](/)[Peptides](/peptides)[Compare](/compare)[Glossary](/glossary)[Blog](/blog)[Calculators](/calculators)[Start Here](/start) [Open the App](https://app.peptrackerpro.com) [Peptides](/peptides)/ IGF-1 LR3 **Research-only content.** This page is for educational purposes and does not constitute medical advice. [Read full disclaimer →](/research-disclaimer) # IGF-1 LR3 Medium Evidence A modified form of IGF-1 with extended half-life, studied for muscle growth and tissue development. Aliases Long R3 IGF-1 +1 more Evidence Medium Evidence Last Updated 2026-05-27 Reading Time 2 min ## Table of Contents 1. [What It Is](#what-it-is) 2. [Why Researchers Study It](#why-researchers-study) 3. [Proposed Mechanisms](#proposed-mechanisms) 4. [Evidence Snapshot](#evidence-snapshot) 5. [Commonly Discussed Benefits](#benefits) 6. [Safety & Cautions](#safety) 7. [Comparisons](#comparisons) 8. [Calculator Tools](#calculator) 9. [Citations](#citations) ## What It Is IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a synthetic 83-amino acid analog of human IGF-1 with two key modifications: an arginine substitution at position 3 and a 13-amino acid N-terminal extension peptide. These modifications reduce binding affinity to IGF-binding proteins (IGFBPs), resulting in a longer biological half-life and greater bioavailability compared to native IGF-1. While endogenous IGF-1 circulates largely bound to IGFBP-3 and is tightly regulated, IGF-1 LR3 remains predominantly in its free, biologically active form. IGF-1 signals through the IGF-1 receptor (IGF-1R), activating the PI3K/AKT and MAPK/ERK pathways to promote cell proliferation, protein synthesis, and glucose uptake in skeletal muscle. In cell culture models, IGF-1 LR3 is approximately 2–3× more potent than native IGF-1 at stimulating cell proliferation due to its reduced IGFBP sequestration. The same enhanced potency raises safety concerns: prolonged, unregulated IGF-1R activation is associated with increased risk of cellular hyperproliferation, and epidemiological data links elevated circulating IGF-1 levels to higher risk of certain cancers (colorectal, prostate, breast). IGF-1 LR3 is classified as a prohibited substance by WADA and is not FDA-approved for any indication. Native IGF-1 (mecasermin/Increlex) is FDA-approved only for severe primary IGF-1 deficiency. Also known as: Long R3 IGF-1, Long Arginine IGF-1 ## Why Researchers Study It IGF-1 LR3 has a significantly longer half-life than native IGF-1 due to its reduced affinity for IGF-binding proteins. This makes it a preferred research tool for studying sustained IGF-1 receptor activation, muscle hypertrophy pathways, and satellite cell-mediated tissue repair in preclinical models. ## Proposed Mechanisms - Binds IGF-1 receptors with similar affinity to native IGF-1 but resists binding protein sequestration - Promotes satellite cell activation and myoblast proliferation - Stimulates protein synthesis through PI3K/Akt/mTOR signaling cascade - Extended half-life allows sustained anabolic signaling in muscle tissue ## Evidence Snapshot Medium Evidence Low Medium High ## Commonly Discussed Benefits [Muscle Growth](/benefits/muscle-growth)[Recovery](/benefits/recovery)[Fat Loss](/benefits/fat-loss) Researching IGF-1 LR3 ? Track it, set reminders, and keep notes in the free app. [Track in App](https://app.peptrackerpro.com/?add=igf-1-lr3) ## Safety & Cautions - Potent growth factor with theoretical cancer risk concerns - May cause hypoglycemia - Not selective — promotes growth in all tissues - Not FDA-approved; requires careful medical consideration ## Comparisons See how IGF-1 LR3 compares to related peptides: [IGF-1 LR3 vs CJC-1295](/compare/igf-1-lr3-vs-cjc-1295) [IGF-1 LR3 vs IGF-DES](/compare/igf-1-lr3-vs-igf-des) [IGF-1 LR3 vs Ipamorelin](/compare/igf-1-lr3-vs-ipamorelin) [IGF-1 LR3 vs PEG-MGF](/compare/igf-1-lr3-vs-peg-mgf) ## Calculator Tools Use our research tools to explore dosing and reconstitution data: [Reconstitution Calculator](/calculators) ## Citations 1. \[1\] Francis GL. et al. — Insulin-like growth factors 1 and 2 in bovine colostrum. Biochem J. 1988 [PubMed](https://pubmed.ncbi.nlm.nih.gov/) ### Keep researching in the app - Log IGF-1 LR3 to your private tracker - Set a dosing reminder - Compare it side-by-side with your stack [Open PepTracker Pro Free](https://app.peptrackerpro.com/?add=igf-1-lr3) [Browse more peptides](/peptides) ## Related Peptides ### CJC-1295 Medium Evidence A growth hormone releasing hormone analog studied for stimulating growth hormone secretion. [Muscle Growth](/benefits/muscle-growth)[Fat Loss](/benefits/fat-loss)[Recovery](/benefits/recovery)[Sleep](/benefits/sleep)+1 more [View Details](/peptides/cjc-1295) [\+ Compare](/compare?select=cjc-1295)[](https://app.peptrackerpro.com/?add=cjc-1295) ### IGF-DES Low Evidence A truncated form of IGF-1 with high potency and rapid local activity at the site of administration. [Muscle Growth](/benefits/muscle-growth)[Recovery](/benefits/recovery) [View Details](/peptides/igf-des) [\+ Compare](/compare?select=igf-des)[](https://app.peptrackerpro.com/?add=igf-des) ### Ipamorelin Medium Evidence A selective growth hormone secretagogue studied for targeted GH release with fewer side effects than other GH peptides. [Muscle Growth](/benefits/muscle-growth)[Fat Loss](/benefits/fat-loss)[Recovery](/benefits/recovery)[Sleep](/benefits/sleep)+1 more [View Details](/peptides/ipamorelin) [\+ Compare](/compare?select=ipamorelin)[](https://app.peptrackerpro.com/?add=ipamorelin) ### PEG-MGF Low Evidence A PEGylated splice variant of IGF-1 studied for muscle repair and satellite cell activation, with an extended half-life compared to native MGF. [Muscle Growth](/benefits/muscle-growth)[Recovery](/benefits/recovery)[Wound Healing](/benefits/wound-healing) [View Details](/peptides/peg-mgf) [\+ Compare](/compare?select=peg-mgf)[](https://app.peptrackerpro.com/?add=peg-mgf) [PepTracker Pro](/) Educational peptide information and research tracking tools. Not medical advice. #### Explore - [Peptide Directory](/peptides) - [Compare Peptides](/compare) - [Glossary](/glossary) - [Benefits](/benefits/sleep) #### Learn - [Blog](/blog) - [Calculators](/calculators) - [Start Here](/start) - [About](/about) #### Legal - [Editorial Policy](/editorial-policy) - [Research Disclaimer](/research-disclaimer) - [Disclaimer](/disclaimer) - [Privacy Policy](/privacy) - [Terms of Service](/terms) - [Contact](/contact) © 2026 PepTracker Pro. Educational purposes only. Not medical advice. Always consult a licensed healthcare provider.